Tempstar furnace diagnosis?

Reply

  #1  
Old 02-08-08, 01:12 PM
Member
Thread Starter
Join Date: Jan 2006
Location: south Alabama
Posts: 73
Question Tempstar furnace diagnosis?

Here is my background info before I begin:

#1 living area: south Alabama
#2 ambient temperature: oppressive humidity & heat during the summer but very mild during the winter
#3 house style & construction: very old brick house...1950's or thereabouts
#4 Make, model, & age of equipment:
I'll have to guess at the age of the equipment as being somewhere around 11 - 13 years old. It's a Tempstar forced air furnace (with cooling unit) too. As a matter of fact, here is the specifications tag on the side of the unit:

http://i244.photobucket.com/albums/g...g?t=1202495179
#5 Fuel type: natural gas
#6 Thermostat type: not sure about this....however here are a couple of pics that may do a better job of explaining than I can:

http://i244.photobucket.com/albums/g...rmostat001.jpg
http://i244.photobucket.com/albums/g...rmostat002.jpg


I seem to have lost my heat yesterday (and I don't know the first thing about furnaces) so I was wondering if anyone might be able to steer me in the right direction so that I may be able to accurately assess the situation..

I've done some preliminary leg work to see what might be wrong and I have noticed that:

1. when the switch on the indoor thermostat is on "Heat", then I can turn the thermostat dial all the way backward and all the way forward and the heat never comes on.

2. if I leave the indoor thermostat on "Heat" and switch the fan from "Auto" to "ON", then I can feel air moving out of the duct/vents into the house...however, the air is not warm at all.

3. I can switch the unit from "Heat" to "A/C" and I can turn the indoor thermostat dial so that the air conditioning comes on.

4. When I got the air conditioning to come on, then I went outside to observe the unit in action and noticed that the blower fan (on top of the unit) does indeed work and seems to spin just like it normally would when the air conditioning is on.

5. When I switch the indoor thermostat to "Heat" and turn the fan switch from "Auto" to "ON", then when I go outside to observe the unit in action, the only thing I notice is that I can hear the slight rumble of air moving inside the unit.


(this is my gas hookup for the furnace):
http://i244.photobucket.com/albums/g...Furnace004.jpg

Anyone got any ideas?...

Could it just be a bad thermostat?...or could it be that my (gas) pilot light has gone out?..or is it something more sinister than that?

A big thanks to all those who reply!
 
Sponsored Links
  #2  
Old 02-08-08, 01:17 PM
Ed Imeduc's Avatar
Member
Join Date: Aug 2002
Location: Mountain Williams Missouri
Posts: 18,389
Wink

You have fan and AC so that means you have power and the 24V and tstat works so yes check out the pilot and gas valve. do you get 24V power to the gas valve.? Does it have a standing pilot??? is it clean ??
 
  #3  
Old 02-08-08, 01:42 PM
Member
Thread Starter
Join Date: Jan 2006
Location: south Alabama
Posts: 73
Originally Posted by Ed Imeduc View Post
You have fan and AC so that means you have power and the 24V and tstat works so yes check out the pilot and gas valve. do you get 24V power to the gas valve.? Does it have a standing pilot??? is it clean ??
Thanks for the reply, Ed!

Where can I find the gas valve at on the unit?...and how can I check to see if I'm getting 24V power to it (I've got a voltmeter that I've been itching to use )?

Also, what is a standing pilot and how would I know whether or not that I have one?

As for the 'clean' part, then I'm not sure about that either...I would tend to doubt it though (I should probably refer to the 'sticky' at the top of the board for instructions on how to clean it).
 
  #4  
Old 02-09-08, 04:55 AM
pflor's Avatar
Member
Join Date: Dec 2007
Location: U.S.A.
Posts: 1,127
http://forum.doityourself.com/showthread.php?t=334473

From your picture, if you follow the gas line (which shows going under the unit), at the very end of it is the gas valve.

Also, click on the link above, it will bring you to a reply of mine attached to your previous thread.

And the following link shows the specs for your unit
http://64.233.169.104/search?q=cache...lnk&cd=5&gl=us

picture showing gas valves and modules follows
 
  #5  
Old 02-09-08, 05:57 AM
Member
Thread Starter
Join Date: Jan 2006
Location: south Alabama
Posts: 73
Re:

Originally Posted by pflor View Post
http://forum.doityourself.com/showthread.php?t=334473

From your picture, if you follow the gas line (which shows going under the unit), at the very end of it is the gas valve.

Also, click on the link above, it will bring you to a reply of mine attached to your previous thread.

And the following link shows the specs for your unit
http://64.233.169.104/search?q=cache...lnk&cd=5&gl=us

picture showing gas valves and modules follows

Thanks for the help, pflor!

I saw your previous reply and I am currently searching the premises for the original documentation for this unit (I know it's around here somewhere! )

Now that you've given me a starting point, then I'll go see if I can locate all of the things that you told me to go look at.

Hopefully, I can get to the root of the problem by the end of the day.
 
  #6  
Old 02-09-08, 12:23 PM
Member
Thread Starter
Join Date: Jan 2006
Location: south Alabama
Posts: 73
Re:

Originally Posted by pflor View Post
Your unit is a packaged system with gas heat and electric cooling (compressor). It has an inducer blower and Hot Surface Ignition (HSI).

The company that manufactured it, if I'm correct, now calls their newer versions of this same unit "Comfortmaker".

Your unit is quite old, I have not being able to retrieve the schematic, but from knowing the type of ignition (HSI), and having an inducer blower, this is what could have gone bad:
(1) the pressure switch
(2) the ignitor
(3) the inducer blower
(4) the electronic module

If you think you can get the schematic (by the unit or if you have the manual), scan it and post it via PhotoBucket.

In the meantime, check as follows:
* see if the inducer blower comes ON at all (not the house blower, but the one outside the house, inside your unit, the one that moves the combustion gases)
* If the combustion blower runs, see if the ignitor gets cherry red (there must be a glass visor there somewhere)
* the module is likely a Honeywell or a Robertshaw. If you can take note of its M/N, I may be able to tell you what to check for.
OK...I know some more now:

If what is pictured here is what is referred to as the inducer blower:
http://i244.photobucket.com/albums/g.../Blower001.jpg

...then it does indeed come on.

And if what is pictured here is what is referred to as the igniter:
http://i244.photobucket.com/albums/g...Igniter001.jpg

...then it DOES NOT ever heat up at any point.


And if what is pictured here is what is referred to as the electronic module:
http://i244.photobucket.com/albums/g...l/Valve002.jpg

..then it is indeed a Honeywell module.

Also, this may be the model # for the module printed on this tag:
http://i244.photobucket.com/albums/g.../Module001.jpg

Am I correct now in assuming that the problem can now be narrowed down to either the igniter or the electronic module?..

If so, then how can I somehow test the electronic module to make sure that it is indeed functioning correctly?

Thanks.
 
  #7  
Old 02-09-08, 12:45 PM
pflor's Avatar
Member
Join Date: Dec 2007
Location: U.S.A.
Posts: 1,127
Yes, yes and yes...excellent troubleshooting.

#1 yes - your first picture shows indeed the inducer blower motor (which you report as operating properly)

#2 yes - 2nd pic is the ignitor/pilot assembly. The way your ignitor should operate is that first, the ignitor gets juice and glows (the black component directly in front of the pilot burner hood assembly); second, the gas valve sends gas through the small "aluminum" pipe (the pilot gas line) and off the pilot burner hood; third, the ignitor (still glowing red) ignites the gas coming off the pilot burner hood; fourth a small electrical current is sent from the module via the flame-rod (the small toothpick look alike metal shaft behind the igniter)...this electrical signal literally jumps into the pilot burner flame and "swims" towards the "fork-looking" metal plate above it...reaches it and goes back to the module to tell the module that there is a flame and is safe to ignite the main burners. the flame-rod should not touch the the fork-shaped metal section; in the picture it appears that it's touching it

#3 yes - the last pic is a module...more than that, your unit has Honeywell's Smart Valve. This is not only a module but a gas valve AND module combo.

See if the ignitor glows red on a call for heat. If it doesn't replace the ignitor/pilot burner/electrode assembly

Maybe the flame off the pilot burner is weak and not engulfing the gap between the flame-rod (which is an electrode) and ground assembly..the fork-shaped thing (which is another electrode)...the orifice (inside the hood) may be dirty, or pilot-gas-pressure may need to be increased.

Maybe the two electrodes are touching each other (this is a no go)...they should be close to each other but without touching each other, and the flame should engulf both of them.

I don't want to get any more wordy, check what I've suggested and provide additional feedback.
 
  #8  
Old 02-09-08, 12:48 PM
pflor's Avatar
Member
Join Date: Dec 2007
Location: U.S.A.
Posts: 1,127
I still would love to see the schematic for this unit (if you could find it, of course). Else, we'll just keep shooting darts until we get to the bottom of this problem. One way or the other.
 
  #9  
Old 02-09-08, 02:06 PM
Member
Thread Starter
Join Date: Jan 2006
Location: south Alabama
Posts: 73
Re:

Originally Posted by pflor View Post

the flame-rod should not touch the the fork-shaped metal section; in the picture it appears that it's touching it
It actually doesn't...it's just the camera angle instead. I'm 100% positive that they don't touch each other...

Originally Posted by pflor View Post
#3 yes - the last pic is a module...more than that, your unit has Honeywell's Smart Valve. This is not only a module but a gas valve AND module combo.

See if the ignitor glows red on a call for heat. If it doesn't replace the ignitor/pilot burner/electrode assembly
That ignitor never glows red and I have never once felt any kind of warmth coming from it at all no matter what I set my indoor thermostat to....it stays cold no matter what I do.

Originally Posted by pflor View Post
Maybe the flame off the pilot burner is weak and not engulfing the gap between the flame-rod (which is an electrode) and ground assembly..the fork-shaped thing (which is another electrode)...the orifice (inside the hood) may be dirty, or pilot-gas-pressure may need to be increased.

Maybe the two electrodes are touching each other (this is a no go)...they should be close to each other but without touching each other, and the flame should engulf both of them.

I don't want to get any more wordy, check what I've suggested and provide additional feedback.
If the ignitor never heats up (and never glows obviously), then I won't be getting a pilot flame...correct?

Also, it seems logical (to me anyway) that there would be a slight smell of gas (because of gas emerging from the hood)....however, I don't ever smell gas and I don't ever feel even the slightest hint of gas emerging from around the hood....is this normal at all?
 
  #10  
Old 02-09-08, 04:06 PM
pflor's Avatar
Member
Join Date: Dec 2007
Location: U.S.A.
Posts: 1,127
DixieH, I'm away from home at friends' house...this P.C. does not have the software I have in mine. I'm leaving out for dinner & social. I'm attaching a PDF file from Honeywell. look at pgs 6 & 11.

I think the igniter is bad, but you've got to check for 24V first (or lack thereof) prior to condemning it. Also, there's more than just the smart valve working together with it. What do you have? It would be just too much luck that you also have the ST9120 shown on pg-6

http://customer.honeywell.com/techli...0s/69-1270.pdf
 
  #11  
Old 02-09-08, 08:37 PM
Member
Thread Starter
Join Date: Jan 2006
Location: south Alabama
Posts: 73
Re:

Originally Posted by pflor View Post
I think the igniter is bad, but you've got to check for 24V first (or lack thereof) prior to condemning it. Also, there's more than just the smart valve working together with it. What do you have? It would be just too much luck that you also have the ST9120 shown on pg-6

http://customer.honeywell.com/techli...0s/69-1270.pdf
No sweat there, pflor...it's been awfully mild here today (very pleasant actually) and no need for the furnace..

I think I know what you've been looking for now...I made a couple of pics of this as soon as I popped the panel off earlier today but I forgot to include the links to the pics:

(connection diagram pics):
#1 http://i244.photobucket.com/albums/g...elLabel003.jpg

#2 http://i244.photobucket.com/albums/g...elLabel004.jpg

#3 http://i244.photobucket.com/albums/g...elLabel005.jpg
It doesn't look like the ST9120 (on page 6) that you described...

Also, I've got a voltmeter that I can use to check for 24V, however I don't know where (and on what component(s)) to attach the leads to.
 
  #12  
Old 02-10-08, 05:34 AM
pflor's Avatar
Member
Join Date: Dec 2007
Location: U.S.A.
Posts: 1,127
Great pics., I'll be getting back to you in the course of the day with feedback
 
  #13  
Old 02-10-08, 09:28 AM
pflor's Avatar
Member
Join Date: Dec 2007
Location: U.S.A.
Posts: 1,127
O.K. let's see if I leave you with some tests to perform before I run out of the house for Church and later a soccer game of my son...

1- Let's check to see if the module is doing its share of work.
Your module has 5 number and 6 letter terminals (1-thru-5 and C,G,Y,W,R). Put a jumper between W and R on the module to simulate the call for heat from the thermostat (switch the t-stat inside the house to OFF)

2- You should now read 24V between terminals 2&4 on the module. If you don't (say, your meter reads "0", the module is defective since you're calling for heat)

3- You should also read 24V between terminals 1&3 ON THE HONEYWELL SMART VALVE. If not, a wire is loose between the module (terminals 2&4) and terminals 1&3 on the smart valve. Correct the problem.

You should read 0-volts between terminals 1&6 on the module if the limit switch is closed (an open limit with the furnace just beginning a heating cycle indicates a bad limit). If not, put a jumper between terminals 1&6 to simulate a closed limit

4- Leaving terminal 3 on the module, a blue wire goes to the rollout switch; from the other terminal of this switch a red wire goes to the pressure switch, and from the opposite end of this second switch, a blue wire ends up on terminal 4 on the gas valve. With the inducer blower running, those two switches should be closed...check for "0" volts across the terminals of each one of these two switches. If you read 24V in either one, the switch(es) is(are) open. In the case of the rollout switch, there's a small reset button...push. In the case of the pressure switch, TEMPORARILY put a jumper between its two terminals. See if the igniter starts glowing

5- If the igniter did not glow, pull the 4-prong connector that connects the ignitor/electrode assembly to the smart valve. Identify the two terminals that feed the ignitor (they should be contiguous to one another) and, on the valve's side, test for 24V across these two terminals (on the smart valve side, not the cable that goes to the igniter). If you do read 24V, the ignitor is bad and must be replaced

6- Remember to remove the "temporary jumper" mentioned on step-4

I look forward to your feedback.
 
  #14  
Old 02-10-08, 01:57 PM
pflor's Avatar
Member
Join Date: Dec 2007
Location: U.S.A.
Posts: 1,127
correction

On my previous posting (#13), item-1 says that the module has 5-number and 6-letter terminals. Actually, is the opposite, 6-number (1-thru-6) and 5-letter terminals is what you have there.

Additional feedback: the "pressure switch" mentioned on item-4 on the previous posting is a N.O. switch (N.O.= normally open, when the inducer blower is OFF). On a call for heat from the thermostat, one of the first things the module does is a self-test, and checking that this switch is open is perhaps the very first thing it does. Furthermore, after the inducer is up and running, the contacts of the switch MUST close, else the unit will not fire. And if the contacts were closed prior to the call for heat, the unit will not fire either.

You can check the condition of the switch using your voltmeter. You should read 24V across its two terminals prior to the call for heat (when the inducer blower is still in the OFF mode), and, 0V once the inducer blower kicks ON. If this does not happen, your switch may be defective.
 
  #15  
Old 02-10-08, 04:27 PM
pflor's Avatar
Member
Join Date: Dec 2007
Location: U.S.A.
Posts: 1,127
We're on a roll...
I've been able to find out just about everything regarding your unit. The website below would help you do the same to keep copies of them (they are PDF files)
http://www.tempstardlr.com/go/index....77&p=95&ps=520

Your unit seems to have a Honeywell ST9120 as I suspected. Picture follows. Please confirm that this suspicion of mine is correct.

 
  #16  
Old 02-10-08, 04:53 PM
Member
Thread Starter
Join Date: Jan 2006
Location: south Alabama
Posts: 73
Re:

Thanks for all the help, pflor!

Unfortunately, I didn't get to execute all of your instructions today ....I got tangled up with something else...

However, I did get as far as step #1 (before darkness finally set in upon me):
"Put a jumper between W and R on the module to simulate the call for heat from the thermostat"


That's as far as I got and I had to abandon my adventure because of darkness..

However, putting the jumper wire between W & R did indeed kick the inducer fan on and it also made the igniter glow red and then I saw the furnace light up..

I'm going to take another crack at this tomorrow in the daylight..

Also, I'm completely a novice at this and I just wanted to make sure that any kind of wire (for the jumper) will do and I wanted to also make sure that I'm supposed to leave the existing wires plugged in to the terminals (when I stick the end of the test leads for the voltmeter to them)...is this correct?

If so, then I have to pull the connectors on the ends of the wires away from the terminal just a bit to get the test leads to make contact with the terminals (it's definitely a tight squeeze).
 
  #17  
Old 02-10-08, 04:57 PM
Member
Thread Starter
Join Date: Jan 2006
Location: south Alabama
Posts: 73
Re:

Originally Posted by pflor View Post
We're on a roll...
I've been able to find out just about everything regarding your unit.

Your unit seems to have a Honeywell ST9120 as I suspected. Picture follows. Please confirm that this suspicion of mine is correct.
That looks a whole lot like it..

I only got to spend about 30 minutes with it today, however this diagram does indeed look very much like the one in my unit.
 
  #18  
Old 02-10-08, 05:42 PM
pflor's Avatar
Member
Join Date: Dec 2007
Location: U.S.A.
Posts: 1,127
Originally Posted by DixieH View Post
I did get as far as step #1 (before darkness finally set in upon me):
"Put a jumper between W and R on the module to simulate the call for heat from the thermostat"
Putting the jumper wire between W & R did indeed kick the inducer fan on and it also made the igniter glow red and then I saw the furnace light up..).
Did the furnace light-up? or was it the pilot burner that lighted-up? Don't forget to remove the jumper!!! and when you try again tomorrow, I want to know how long does the furnace stays firing. Since the ignitor is turning red, it is not defective and not the problem...maybe flame sensing is the problem...more on that tomorrow after I get feedback from you as to what's happening each step of the way

Originally Posted by DixieH View Post
Also, I'm completely a novice at this and I just wanted to make sure that any kind of wire (for the jumper) will do and I wanted to also make sure that I'm supposed to leave the existing wires plugged in to the terminals (when I stick the end of the test leads for the voltmeter to them)...is this correct?

If so, then I have to pull the connectors on the ends of the wires away from the terminal just a bit to get the test leads to make contact with the terminals (it's definitely a tight squeeze).
Those connectors should be metal (spade - male quick connectors). I'm not sure what you mean when you write "tight squeeze"...hook up your probe's lead wires at the terminals of the switches, not the board prongs.

Pic of a jumper wire follows. You may buy a set at the nearest Radio Shack. They only need to be about 6 inches long each.

 
  #19  
Old 02-10-08, 09:39 PM
Member
Thread Starter
Join Date: Jan 2006
Location: south Alabama
Posts: 73
Re:

Originally Posted by pflor View Post
Did the furnace light-up? or was it the pilot burner that lighted-up? Don't forget to remove the jumper!!! and when you try again tomorrow, I want to know how long does the furnace stays firing. Since the ignitor is turning red, it is not defective and not the problem...maybe flame sensing is the problem...more on that tomorrow after I get feedback from you as to what's happening each step of the way
In this order I saw/heard:

#1 igniter begin glowing red
#2 heard the gas emerging from the pilot hood
#3 saw the pilot flame light
#4 saw the whole furnace come on

Obviously I wasn't prepared for the whole furnace to come on at that point, so I immediately disengaged the jumper wire (I should probably upgrade to the kind of jumper wire in your pic...the only thing I had at the time was an ultra-thin strand from the inside of a section of inside telephone wire! )

Originally Posted by pflor View Post
Those connectors should be metal (spade - male quick connectors). I'm not sure what you mean when you write "tight squeeze"...hook up your probe's lead wires at the terminals of the switches, not the board prongs.
I have a multimeter like this one:



....and the terminals are really, really spaced close to one another so that it's difficult to stick these leads to metal (the spade connectors are tucked inside plastic coating/sheathing and not exposed...so I have to pull 'em out a little so that the ends of the multimeter leads can touch some metal instead of the plastic sheathing on the spade connectors)
 
  #20  
Old 02-11-08, 12:51 AM
pflor's Avatar
Member
Join Date: Dec 2007
Location: U.S.A.
Posts: 1,127
Well... ...since the whole furnace came ON, there's likely no need for all the multi-step troubleshooting I mentioned a few postings ago. The inducer, module, smart valve and ignitor are all doing their jobs. IF anything at all, maybe the pilot flame is too weak and does not engulf the two electrodes in front of it (the ones that appeared to me to be touching)...and if so...the main burners will be turned OFF on safety within 5 seconds or so after light-up...a dirty pilot burner hood (with rusty metal flakes in it) may be all that's happening here.

Next time you go near the monster put the jumper once more between R and W. The inducer will turn ON, the igniter will glow, the tiny pilot burner will light and soon after the main burners will fire up too. DON'T remove the jumper. I need to know from you how long the main burners do stay ON before shutting themselves OFF. About 30 seconds (or so) after the main burners kick ON, the main (house) blower should kick ON...afterwards, if all is normal, the pilot stays lit, main burners continue firing and house blower remains ON. If the house blower does not come ON, there is your problem...the furnace will likely shut itself OFF on safety within a minute of operation.

If all is good and dandy, all that I mentioned in the previous page should happen, in the order mentioned. After about 5 minutes of normal operation, remove the jumper. Have someone inside the house turn the thermostat to the heating mode and spin the dial to..say...80F. You stay by the unit. If the normal light-up sequence does not happen, your t-stat is defective (or the W wire is chewed-up somewhere). If the unit fires and all is normal but within 2 minutes or less turns itself OFF, you have an improper anticipator setting at the thermostat (or the thermostat is flaky and should be replaced)

If it doesn't occur normally, I need to know at what point the start-up sequence got off track and how.

Buy for yourself a set of jumper wires at a Radio Shack. They come in handy
 
  #21  
Old 02-11-08, 08:27 AM
Member
Thread Starter
Join Date: Jan 2006
Location: south Alabama
Posts: 73
Re:

Originally Posted by pflor View Post
Well......since the whole furnace came ON, there's likely no need for all the multi-step troubleshooting I mentioned a few postings ago. The inducer, module, smart valve and ignitor are all doing their jobs. IF anything at all, maybe the pilot flame is too weak and does not engulf the two electrodes in front of it (the ones that appeared to me to be touching)...and if so...the main burners will be turned OFF on safety within 5 seconds or so after light-up...a dirty pilot burner hood (with rusty metal flakes in it) may be all that's happening here.

Next time you go near the monster put the jumper once more between R and W. The inducer will turn ON, the igniter will glow, the tiny pilot burner will light and soon after the main burners will fire up too. DON'T remove the jumper. I need to know from you how long the main burners do stay ON before shutting themselves OFF. About 30 seconds (or so) after the main burners kick ON, the main (house) blower should kick ON...afterwards, if all is normal, the pilot stays lit, main burners continue firing and house blower remains ON. If the house blower does not come ON, there is your problem...the furnace will likely shut itself OFF on safety within a minute of operation.

If all is good and dandy, all that I mentioned in the previous page should happen, in the order mentioned. After about 5 minutes of normal operation, remove the jumper. Have someone inside the house turn the thermostat to the heating mode and spin the dial to..say...80F. You stay by the unit. If the normal light-up sequence does not happen, your t-stat is defective (or the W wire is chewed-up somewhere). If the unit fires and all is normal but within 2 minutes or less turns itself OFF, you have an improper anticipator setting at the thermostat (or the thermostat is flaky and should be replaced)

If it doesn't occur normally, I need to know at what point the start-up sequence got off track and how.

I took at another crack at this a few minutes ago:

#1 I put the jumper wire on between R and W (got some jumper leads from Radio Shack )

#2 Saw the igniter fire up

#3 Saw the pilot flame come on

#4 Saw the burners light up

I let the thing run for about 15 minutes or so actually....the burners never shut off at all (until I disconnected the jumper leads of course).

I tried as best I could to put the leads of my voltmeter on terminals 2 & 4 (I'm about 80% positive that I was able to contact the leads of the meter to the terminals and being able for the leads to contact metal instead of the plastic sheathing covering the terminal wire spades)...

I got a zero volt reading when the voltmeter leads were contacting the metal on the terminals...

I'm about to do the part you said about having someone inside the house operate the thermostat in just a few minutes..

I took a few photos of my adventure this a.m. so far:

(Burner Pics):
http://i244.photobucket.com/albums/g.../Burner001.jpg
http://i244.photobucket.com/albums/g.../Burner002.jpg
http://i244.photobucket.com/albums/g.../Burner003.jpg

(pics of the board....and yes it's difficult to have enough operating room to touch the ends of the voltmeter leads to the terminals):
http://i244.photobucket.com/albums/g...s/Board001.jpg
http://i244.photobucket.com/albums/g...s/Board002.jpg

Also,...as near as I can tell...the house blower never cut off (otherwise the safety would have shut the burners off like you said)..

You said 0 volts between 2 & 4 would indicate a bad board...so maybe the board is fried?

I'll be back in a few minutes or so after I try the thermostat test..
 
  #22  
Old 02-11-08, 09:11 AM
pflor's Avatar
Member
Join Date: Dec 2007
Location: U.S.A.
Posts: 1,127
DixieH:
The unit is firing and doing so quite well (from what you have just reported). The board is thereby O.K., it is "not" fried.

The problem is somewhere between the thermostat inside the house and the R-W terminals by the unit.

Maybe, just maybe, you did not wait long enough when you tried to get heat going and the thermostat seemed not to be able to get the unit going. It takes a minute or so between the start of the call for heat and the registers blowing warm air throughout the house. It's a wait and see game. In cooling the house blower kicks ON right away, not so in the heating mode.

I'm at work now. The firewall in our system here at work does not allow me to access your most recent pictures. I can't wait to see them after I get back home around 5PM or so.

Keep up the good work.

If from the thermostat you cannot get the furnace going, remove the thermostat (but not the sub-base) and jumper between R and W at the subbase. If now the furnace fires-up, the t-stat is bad. If you need help/directions performing this last test, let me know.
 
  #23  
Old 02-11-08, 10:17 AM
Member
Thread Starter
Join Date: Jan 2006
Location: south Alabama
Posts: 73
Re:

Originally Posted by pflor View Post
DixieH:
The unit is firing and doing so quite well (from what you have just reported). The board is thereby O.K., it is "not" fried.
I just wanted to make sure about this...

No matter what I do, then I still get a zero volt reading when I hook up the leads of the voltmeter between the #2 & #4 terminals..

Also, I did a voltage test on the #1 & #3 terminals on the smart valve and it gave me a reading of 26.2..

Originally Posted by pflor View Post
The problem is somewhere between the thermostat inside the house and the R-W terminals by the unit.

Maybe, just maybe, you did not wait long enough when you tried to get heat going and the thermostat seemed not to be able to get the unit going. It takes a minute or so between the start of the call for heat and the registers blowing warm air throughout the house. It's a wait and see game. In cooling the house blower kicks ON right away, not so in the heating mode.

If from the thermostat you cannot get the furnace going, remove the thermostat (but not the sub-base) and jumper between R and W at the subbase. If now the furnace fires-up, the t-stat is bad. If you need help/directions performing this last test, let me know.
Actually, this part was a little bizarre..

I called up heat using the jumper wire and then unhooked the jumper after 5 minutes (just like you said to do)..

Then I did the thermostat test (flipped thermostat's heat switch to "ON" and fan to "AUTO") and watched while my helper turned the dial to 80..

The thermostat worked this time...

However, when the whole problem began then it was simply a result of the thermostat not cranking up the furnace at all (no matter how long I left it turned up)..

Also, after I got the thermostat to turn it on then the also never turned itself off (until I turned the dial down again)..

In other words, the thermostat seems to work as expected....however, I could never get it to work until the unit was jumped (or "pre-heated")..

I wonder if it will work after the unit has been off for awhile after it has had a chance to cool off?

Should I just go ahead and get another thermostat anyway now?....it's pretty old anyway..

Do I need any particular kind of thermostat (if I need to get one)?....or can I just grab one at the hardware store or Lowe's?

Thanks once again for all the help, pflor!....you're a life-saver!
 
  #24  
Old 02-11-08, 11:13 AM
pflor's Avatar
Member
Join Date: Dec 2007
Location: U.S.A.
Posts: 1,127
I like these:
http://customer.honeywell.com/TechLi...0s/50-9278.pdf
But anything would do. Just make sure is compatible with gas heat and central a.c.
 
  #25  
Old 02-18-08, 09:23 PM
Member
Thread Starter
Join Date: Jan 2006
Location: south Alabama
Posts: 73
Re:

Sorry to keep this thread alive, pflor...however, I had to go out of town for a week (before I could put a brand new thermostat on)..

Anyway, I went and got another thermostat while I was out of town and I just have finished putting it on a couple of hours ago (Honeywell Model #RTH230B, Programmable Thermostat):

http://i244.photobucket.com/albums/g...ce/RTH230B.jpg

I'm nearly positive that I've got the new T-stat wired up correctly (someone can double-check me on that)...

Anyway, I've got the identical problem now that I had with the old thermostat in that I can turn the thermostat setting up so that the thermostat "clicks" (the old thermostat didn't make the "click" sound though) and indicates (digitally) that it is turning on the furnace at that point..

Of course, only the inducer motor ever turns on while the rest of the furnace stays quiet (just like before)..

Now there appears to be another difficulty in that I can no longer simulate the call for heat (jumping 'R' and 'W' with a wire)..

Now when I jump 'R' & 'W', then the igniter doesn't glow at all (and of course the furnace never comes on)...

Whatever the case may be, then I'm keeping the brand new thermostat because I have discovered that the old thermostat contains mercury (BTW, anyone know how to dispose of mercury properly?).
 
  #26  
Old 02-19-08, 03:07 AM
pflor's Avatar
Member
Join Date: Dec 2007
Location: U.S.A.
Posts: 1,127
Hi again...
The thermostat wiring looks good. 4 wires (red=r, yellow=y, green=g, white=w). I imagine you just did a tit-for-tat swap using the old t-stat as a reference. In other words, if the red-wire was connected to the r-terminal in the old t-stat, is now connected to the r-terminal in the new one (do not remove the jumper between Rc and Rh)...same procedure should have been followed with the remaning wires.

You should be outside, by the furnace, while someone puts a jumper between terminals R and W at the thermostat's subbase (with t-stat removed, just like your last pic shows). As soon as the jumper is put in place, please be very observing (keen attention to detail matters, since you'll be my eyes and ears there) and notice what exactly is happening, in what order and for how long.

The normal light-up procedure, as we have discussed before, should be: 1-inducer starts, 2-ignitor glows, 3-pilot burner lights-up, 4-main gas valve opens (you may even be able to hear its click) and main burners lit-up, 5-after a delay house blower kicks ON.

If I hear from you regarding the step where the normal lit-up sequence is interrupted, I'd be able to tell you where and what to check for.
 
  #27  
Old 02-19-08, 09:00 AM
Member
Thread Starter
Join Date: Jan 2006
Location: south Alabama
Posts: 73
Re:

Originally Posted by pflor View Post
The normal light-up procedure, as we have discussed before, should be: 1-inducer starts, 2-ignitor glows, 3-pilot burner lights-up, 4-main gas valve opens (you may even be able to hear its click) and main burners lit-up, 5-after a delay house blower kicks ON.

If I hear from you regarding the step where the normal lit-up sequence is interrupted, I'd be able to tell you where and what to check for.
I just checked this again..

The inducer starts, but that's where things end now..

The igniter does NOT glow.


It doesn't matter whether I 'hotwire' it either at the circuit board or at the indoor thermostat, the sequence of events fails after the inducer starts..

The crazy thing is that I was able to 'hotwire' it successfully when the old thermostat was on the wall (inducer came on..igniter glowed, etc., etc.) until finally the burners lit and the furnace stayed on..

How come the igniter will now no longer glow anymore?
 
  #28  
Old 02-19-08, 10:34 AM
pflor's Avatar
Member
Join Date: Dec 2007
Location: U.S.A.
Posts: 1,127
Dixie...I'm at work, our firewall here won't allow me access to photos/pics (neither receive/see them, nor send them), so I'm going to try helping you with written directions only, until I get back home later.

First we have to see if the board (Honeywell ST9120) is doing it's share of the job, which is feed 24V power to the smart valve (the Honeywell SV9501 gas valve). There should be a 6-wire harness connecting on one end to a 6-port prong on the board...4 of these 6 wires go to the smart valve. This is what you're looking for:

Board Connector number and wire color on the 6-wire prong that plugs on the board
1-red (R)
2-white (W)
3-blue (BL)
4-black (BK)
5-orange (O)
6-red (R)
The 4 wires from the harness above that go to the smart valve are as follows...Valve Connector numbers and colors shown below. These are inputs to the smart valve
1-black (BK)
2-orange (O)
3-white (W)
4-Blue (BL)

Before trying anything, let's make sure the limit switch is closed. From the board, terminals 1&6 have each a red wire. These red wires connect to the two ends of the limit switch. Make sure you've the system calling for heat, put a jumper between these two terminals...if the system now runs, the problem is your limit...replace.

O.K., here we go:
When there's a call for heat (whether from the t-stat in the house or you bypassing W&R at the unit), there should be 24V between the BK and W wires. If you read 0V, the module is defective.

Second, let's assume you read 24V above.
Again, when there's a call for heat, there should be 24V between the BL and W wires. If you read 0V:
the rollout switch and/or the Pressure switch are open (their normal position is N.C.)...place a jumper, one end of which hooks up to the terminal of the rollout where you have the BL wire that goes to terminal-3 on the board, and hook the other end of the jumper to the terminal of the pressure switch where you have the BL wire that goes to terminal-4 on the smart valve.

If you now read 24V with the jumper in place, either the rollout of the pressure switch (or both) are open...more on that later.

If you still read 0V, the board is bad.


Let's assume that you have performed the above tests and the module has passed them with flying colors...

Third, let's check the smart valve outputs...
There's a 4-wire prong (but only 3 wires) coming off the smart valve and going to the ignitor/pilot assembly. These terminals and destination are as follows:
1-wire that goes to the ignitor
2-wire that goes to the ignitor
3- NO wire connected to this terminal
4- wire that goes to the flame-rod
Remove the plug...make sure there is a call for heat
You should read 24V between terminals 1&2 on the smart valve
If you read 0V, the smart valve is defective...replace

If you read 24V, check the ignitor...24V should light that baby up (make it turn cherry red). If it does not, either the ignitor or its wires is bad. Replace the ignitor/pilot assembly, since I do not think you can only buy the ignitor.

All the while, please be sure that the two electrodes on the ignitor/pilot assembly are not touching each other...if they do so, that's the problem.

I hope this helps.
 
  #29  
Old 02-19-08, 02:15 PM
Member
Thread Starter
Join Date: Jan 2006
Location: south Alabama
Posts: 73
Re:

Originally Posted by pflor View Post
Before trying anything, let's make sure the limit switch is closed. From the board, terminals 1&6 have each a red wire. These red wires connect to the two ends of the limit switch. Make sure you've the system calling for heat, put a jumper between these two terminals...if the system now runs, the problem is your limit...replace.
Performed this test...nothing out of the ordinary happened though (no igniter, no furnace, etc.)

(I hope that this is indeed the limit switch):
http://i244.photobucket.com/albums/g.../Limit0021.jpg

Originally Posted by pflor View Post
O.K., here we go:
When there's a call for heat (whether from the t-stat in the house or you bypassing W&R at the unit), there should be 24V between the BK and W wires. If you read 0V, the module is defective.
My multimeter displays 0.00 between 'BK' and 'W' at all times (whether I make the call for heat or not).

Originally Posted by pflor View Post
Second, let's assume you read 24V above.
Again, when there's a call for heat, there should be 24V between the BL and W wires. If you read 0V:
the rollout switch and/or the Pressure switch are open (their normal position is N.C.)...place a jumper, one end of which hooks up to the terminal of the rollout where you have the BL wire that goes to terminal-3 on the board, and hook the other end of the jumper to the terminal of the pressure switch where you have the BL wire that goes to terminal-4 on the smart valve.
Even though I had already read 0V between 'BK' and 'W', then I went ahead and performed this test also..

The multimeter reads 0.00 between 'BL' and 'W' (whether I make the call to heat or not)..

However (and this is the interesting part)....hooking up the ends of the jumper wire between the 'BL' terminal on the rollout and the pressure switch instantly starts the furnace ignition process (the inducer was already running at this point). Before I even had a chance to realize it, then the burners on the furnace started lighting up.

Originally Posted by pflor View Post
If you now read 24V with the jumper in place, either the rollout of the pressure switch (or both) are open...more on that later.

If you still read 0V, the board is bad.
I still read 0V between both 'BK' and 'W' in addition to 'BL' and 'W'.

Originally Posted by pflor View Post
Let's assume that you have performed the above tests and the module has passed them with flying colors...

Third, let's check the smart valve outputs...
There's a 4-wire prong (but only 3 wires) coming off the smart valve and going to the ignitor/pilot assembly. These terminals and destination are as follows:
1-wire that goes to the ignitor
2-wire that goes to the ignitor
3- NO wire connected to this terminal
4- wire that goes to the flame-rod
Remove the plug...make sure there is a call for heat
You should read 24V between terminals 1&2 on the smart valve
If you read 0V, the smart valve is defective...replace
The multimeter reads 0V between terminals 1 & 2 on the Smart Valve.



As a side note (since I kept getting readings of 0V on all the things you told me to check), then I started having doubts about the functionality of my multimeter...however, I hooked it up to a regular AA alkaline battery and the meter displayed a reading of 1.6 V.

In summary, the only time that furnace ever lit up completely today was when I hooked up the jumper wire between the rollout and the pressure switch and then made the call for heat (using another jumper wire of course).....I did this twice today and the furnace went through the proper sequence of events and lit all the burners both times.
 
  #30  
Old 02-19-08, 03:37 PM
Banned. Rule And/Or Policy Violation
Join Date: May 2007
Location: Wisconsin
Posts: 8,629
Originally Posted by DixieH View Post
In summary, the only time that furnace ever lit up completely today was when I hooked up the jumper wire between the rollout and the pressure switch and then made the call for heat (using another jumper wire of course).....I did this twice today and the furnace went through the proper sequence of events and lit all the burners both times.
From what you say in the quote, you about have it solved. Roll out switch may be bad, or pressure switch is not letting current through it, for a variety of reasons. Test each of these safeties, independently:

With inducer running, use voltmeter set to ac volts and put red test lead on one roll out terminal and the black lead to sheetmetal. Do this on each of the two wires/terminals; incoming and outgoing. Both should have 24 volts, about. Then test pressure switch terminals the same way.

One of those two items is likely "open" and not allowing 24 volts to continue to your igniton control board, which is what is needed to allow the surface ignitor to come on.
 
  #31  
Old 02-19-08, 04:46 PM
pflor's Avatar
Member
Join Date: Dec 2007
Location: U.S.A.
Posts: 1,127
Dixie:
Just came back from a dental appointment.

You sure have it running. Obviously I'm wrong in my assessment of the voltages expected between BK and W as well as BL and W. Is it possible that the voltages I expected you to read would be present if the safeties are all working properly. Limit switches and rollout switches both belong to the family of the so called "safety switches".

From what you describe, you have bypassed either the limit or the rollout switch...in other words (as per schematic...which may not necessarily exactly match what you have there), you have placed one end of the jumper on the side of the rollout where the BL wire is connected (the side that ends up on terminal-3 on the board) and the other on the side of the rollout where the R wire is connected (the side that ends up by the pressure switch)

Rollout switches are resettable...in other words, you push a red button and presto. They look similar to the one shown below. The reset button is pointed at by the red arrow I have drawn.


Standard limit switches are NOT resettable. If the switch that you bypassed with the jumpers does not have the reset button like the one shown in the pic above, it is indeed a high limit switch and you'll need to buy a new one...do NOT just leave the jumpers in place.

At any rate, I'd be willing to bet that you've got this problem nailed down...but the new switch and it'll be like in the fairy tales: ...and they lived happily ever after.
 
  #32  
Old 02-19-08, 05:02 PM
pflor's Avatar
Member
Join Date: Dec 2007
Location: U.S.A.
Posts: 1,127
voltages BK-W & BL-W

If you don't mind, with the furnace up and running, pls kindly take the readings I asked you to take (on that previous post of mine in the afternoon)...b/c it really bugs my mind and I'd like to make sure I get a full understanding of how your ST9120 board operates.

BTW, from the picture you took of your schematic, the limit switch is all by itself , with 2 red wires, one in each one of its terminals...while...rollout+pressure switches are in series with each other (next to each other) and I see BL, R (the red in between the two switches) and BL.

The Honeywell manual shows a slightly different configuration. It shows the Pressure switch all by itself, while the rollout+limit are in series.

Which one is it in your unit?
This could be what threw me off.
 
  #33  
Old 02-19-08, 07:42 PM
Member
Thread Starter
Join Date: Jan 2006
Location: south Alabama
Posts: 73
Re:

Originally Posted by pflor View Post
If you don't mind, with the furnace up and running, pls kindly take the readings I asked you to take (on that previous post of mine in the afternoon)...b/c it really bugs my mind and I'd like to make sure I get a full understanding of how your ST9120 board operates.
10-4 on that, pflor! .....I'm very much like that myself...can't stand to be so close to the answer and never come up with it!...

When daylight comes around once again, then I'll run through them all with the voltmeter again..

Originally Posted by pflor View Post
BTW, from the picture you took of your schematic, the limit switch is all by itself , with 2 red wires, one in each one of its terminals...while...rollout+pressure switches are in series with each other (next to each other) and I see BL, R (the red in between the two switches) and BL.

The Honeywell manual shows a slightly different configuration. It shows the Pressure switch all by itself, while the rollout+limit are in series.

Which one is it in your unit?
This could be what threw me off.
If that is indeed the limit switch that you had me put the jumper on, then it is somewhat isolated from the rest of the furnace components....I had to remove another panel around the corner from the front panel in order to reach it.....it seems to be situated in another compartment along with the house blower fan..

I'm not exactly sure about the configuration....however, a picture is always worth a thousand words:

http://i244.photobucket.com/albums/g...Panel001-1.jpg

The pressure switch is circled in green in the top of the photo while the rollout is circled in green on the bottom of the photo..

Like I said previously, the limit switch was only reachable by removing another separate panel that was around the corner from the front panel where all of the other "important" stuff is! .


Lastly, I started becoming suspicious of that rollout switch last week when you first showed me how to "hotwire" the furnace (using 'R' & 'W')..

I didn't think anything about it at the time, but I was "feeling" around the furnace last week and remember tapping the reset button on the rollout switch...obviously that had an effect because I didn't have any trouble "hotwiring" the furnace back then..

When I was trying to "hotwire" it earlier today though, then the furnace never would come on.....however, I remembered pushing that button last week and figured that there wouldn't be any harm if I were to push it again late this afternoon..

Voila! The call for heat was successful after I hit the button.....so I let the furnace run for about 25 minutes or so and then I took the jumper wire off...

So then I figured I would try using the furnace with the new Honeywell programmable thermostat..

Voila! The thermostat has been controlling the furnace for the past couple of hours..

The only consistent thing that I can see is that the furnace works fine after it has been "jumpstarted" and allowed to run for awhile.....it's only when the furnace is off for an extended period of time that it's impossible to get it to come on again..

I can't figure out for the life of me why either of those switches might not work when the furnace has been off for an extended period of time..

I'll know more when daylight comes around though and I can try out those tests that ecman51 suggested earlier this evening..

Fortunately, this has been an extremely mild February so far and the furnace has not been an imperative luxury..

Thanks, pflor!
 
  #34  
Old 02-20-08, 01:44 AM
pflor's Avatar
Member
Join Date: Dec 2007
Location: U.S.A.
Posts: 1,127
Yup...your last pic shows it all. The controls in your unit are just like the schematic you photographed shows them to be. In other words, Pressure AND rollout switches in series with each other (clearly shown in the last pic you posted yesterday night), while the limit is the lone ranger you showed in a pic. yesterday afternoon, with the black jumper attached to it (the one with the 2 red wires).

Limit switches are there to sense supply air temperatures, and that is why you saw it located by the blower compartment. As I said, they are not resettable...they open up if the supply air temp is abnormally hot, turning the gas OFF (their contacts automatically close again once the air temperature is normal again...if the contacts remain open, the switch is defective and must be replaced).
Rollout switches are always by the flames, sensing abnormally high temps by the burner box (say, caused by a flame "rolling out" of the unit). They are of the manual reset type. This is the switch that you have now reported pushing its reset button...unknowingly, you resetted that switch the last time around, and that's why the unit fired up right after you placed the W-R jumper.

I took it upon myself to read, and read, and read again the Honeywell manual for the smart valve, and bottom line is that the voltages I was expecting you to read are correct. Why then "0V" each and every time? b/c the rollout switch contacts had been open all along. When (and if) you do indeed perform the voltage test of the smart valve outputs (the voltage from the valve to the ignitor), the manual says it should be done WITHOUT REMOVING the 4-prong connector from the valve (this is the connector with the 3 wires...2 of which go to the ignitor, the third to the flame-rod)...that makes sense b/c if the flame-rod wire is off, the electrode will spark itself to a safety lockout without firing the burners.

You need now to buy yourself a new rollout switch...and if that was my unit, I'd also buy a limit..."one never knows". For that purpose you'll need to disconnect them and bring them to your HVAC supply store and the person at the counter will give you what is needed. The rollout in all likelihood has become weak and hence your "sporadic" problem. If you need help locating a parts store, just give me an e-howl here at the forum

And yes, pls also perform ecman's test, though with the blower running I expect you to read 24V in both cases, b/c the inducer blower AND pressure switch seem to be doing their jobs (24V on one terminal and 0V on the other - with the blower running - would indicate an open switch). After the inducer blower kicks ON, if there are no obstructions to the airflow, a vacuum develops in the combustion chamber...notice that pink hose that goes from the switch to the blower box (see your last pic)...that's how the switch senses that there is a vacuum and its contacts close. If the blower stops running, or the hose gets lose, or the contacts of the switch are bad, the unit will not fire...same type of job the rollout does, but not by sensing temperatures but pressures

Congrats! you've mastered your unit...warm indoors from now on.
 
  #35  
Old 02-20-08, 11:37 AM
Member
Thread Starter
Join Date: Jan 2006
Location: south Alabama
Posts: 73
Re:

Once again...thanks for all of your patience, pflor!..

I discovered something today that I am quite embarrassed over ..

It seems as though every time that I set out to take a voltage reading on something that I had the multimeter dial on the wrong setting..

I didn't think anything about it until I saw ecman51 mention something about setting the meter on AC Volts.....obviously, I had the meter set on DC Volts instead..

....and obviously that makes a big difference!

So, I set about checking those voltage measurements again (using AC voltage this time)..

Lo and behold, both 'BK' and 'W' (as well as 'BL' and 'W') measure around 26.2 to 26.3 V..

I also did the test that ecman51 recommended (testing each terminal on both the rollout switch and the pressure switch)....did this several times in fact to make sure that I was getting an accurate measurement..

Surprisingly, the voltage on each terminal for both the rollout switch and the pressure switch that I tested gave me readings of approx. 26.1 to 26.3 V..

However, the most surprising thing of all is the fact that the furnace now seems to be acting absolutely normal...the indoor thermostat has worked like a charm every time that I have altered the setpoint for heat either this a.m. or even this afternoon so far..

I have even left the furnace completely off for a few hours today to see if that helps it to replicate the difficulty that I had previously been experiencing.....however, that seems to have had no effect either..

In other words, I can't get it to tear up now and I can't get it to replicate the condition which has previously plagued me for this long now..

I'm not sure what to do now....obviously, I don't want to just go out and start replacing expensive components on a trial and error basis (hoping that I will get lucky).....so until it starts acting up again (if it ever does), then I won't be able to make heads or tales out of the situation..

Obviously, I'm a bit embarrassed about the voltmeter thing....I guess I owe you a Corona now over that!
 
  #36  
Old 02-20-08, 12:31 PM
pflor's Avatar
Member
Join Date: Dec 2007
Location: U.S.A.
Posts: 1,127
Thanks for the update.

Do not make much out of reading 26+ volts instead of 24V. 24 is a nominal value only, transformers typically put out voltages higher than 24V. Say, 26-to-28V, are not unusual values.

I'm glad to hear that the terminals are reading the voltages I expected of them. I started to wonder if I was going nuts

Lastly, limits and rollouts are not expensive, you'd do well in stocking up on them (one of each). I'm not saying replace, them...just have them in a safe place, for a rainy day. With furnaces, the moment you need them the most is when they fail to deliver and not having the spare parts then would keep you cold and running to get the stuff.
 
  #37  
Old 03-02-08, 01:17 PM
Member
Thread Starter
Join Date: Jan 2006
Location: south Alabama
Posts: 73
Question Re:

Sorry for reviving this thread again folks...however, I am experiencing the identical sort of issue that I began to experience a couple of weeks ago..

Recap:

Over the course of several days, then pflor was kind enough to lead me to the specific cause of my troubles..

I finally discovered that my flame roll out switch would trip and shut the furnace off so that it wouldn't come on again (without the reset button of course)..

Oddly enough, the switch will only trip (the majority of the time anyway) when the furnace has gone off for extended periods (maybe like 4 - 5 hours or so)...once you can get the furnace to come on (with the help of the reset button), then the furnace will operate as it normally would..

I bought another switch (it took about a week to deliver because I don't live in a place where I can buy one locally)...and I put it on yesterday..

Sure enough, I am back to square one today...the roll out switch tripped again last night and it won't allow the rest of the ignition sequence to happen..

Everything pflor told me to do previously all checks out correctly...it's just that the switch trips while the furnace is off and prevents it from coming back on..

I have been reading about possible causes for this and here is the list of possible causes that I have come up with so far:

#1 (obviously) flame roll out
#2 flue at end of inducer fan could be obstructed
#3 malfunctioning inducer fan itself
#4 burners need cleaning
#5 heat exchanger is either cracked or rusted

As for #1, I have yet to see any flame jump out from underneath the burner hood during any of the operation periods of the furnace that I have witnessed so far (doesn't necessarily mean that it may not be happening while I'm not standing over it though )..

As for #2, I can put my hand at the end of either opening of the flue tube for the inducer fan and feel the flow of air blowing against it..

As for #3, the inducer fan is (obviously) generating a flow of air..otherwise I wouldn't be able to feel the flow of air leaving the flue..

As for #4, my burners probably do need cleaning, however I can't tell that the burners are obstructed in any way because the flame is a light blue color (as opposed to any yellow color)..

As for #5,...well if the truth be known, then i have no idea what a heat exchanger even looks like or where it's even located at on the unit so that I can inspect it..

I have noticed that there are some areas with some fairly extensive rust on them (don't know if this is related or not)...and just for good measure, then I got took some more photos that are closer in of the areas with rust on them:

http://i244.photobucket.com/albums/g...ce/Rust001.jpg
http://i244.photobucket.com/albums/g...ce/Rust002.jpg
http://i244.photobucket.com/albums/g...ce/Rust003.jpg
http://i244.photobucket.com/albums/g...ce/Rust004.jpg

Finally, since I have gone to such great lengths to solve this issue, then I figured that I might as well learn how to properly clean the furnace while I'm at it...so I was wondering if anyone could tell me the components/areas that need to be cleaned and what materials I should use to clean them with.

Thanks, all!
 
  #38  
Old 03-02-08, 02:25 PM
pflor's Avatar
Member
Join Date: Dec 2007
Location: U.S.A.
Posts: 1,127
Because of the age of this unit and the rust one can see all around, it is possible that there's a cracked heat exchanger here, but only using a scope one could have complete certainty about it.
http://testousa.com/318V/
But how does a cracked heat exchanger cause the nuisance problem you are having? here's my theory:

If the furnace has not been running for quite a few hours, the heat exchanger and vent pipe will both be cold when that long delayed call for heat finally comes. The burners light-up and no too long after the blower kicks ON.

The wall of the heat exchanger has the combustion gases on one side and the circulating house air on the other. The house air will be moving under positive pressure b/c of the blower push, while, the combustion gases are under negative pressure (vacuum) b.c of the location of the inducer motor.

At the moment of the blower start-up, the positive pressure on the air-side will be so great that house air leaks through the crack an into the combustion-air side b/c is under vacuum, momentarily bringing the pressure above atmospheric, causing the flame to be pushed out, towards the rollout. Such does not occur once the furnace has been running for a few cycles b/c by then the heat exchanger and vent pipe are both up to operating temperature, creating a deeper vacuum (on the combustion side), able to move upwards any house-air leaking through the crack into the combustion-air side.

How can you test if this is indeed what is happening?
Turn the furnace OFF for a few hours. Then, go by the furnace, remove the access door and jump between R&W (simulating the call for heat). The inducer will kick ON and soon after the burners will ignite. When time comes for the main (house) blower to kick ON, it is then that I would expect a flame rollout situation (should a large crack exists) b/c of the difference in pressure (between the two sides of the heat exchanger) which I explained above.

So do some more detective work and let us know what exactly is happenning.

If the flame is indeed rolling out b/c of a cracked heat exchanger, time has come to start planning for a replacement furnace unless you can still find out a replacement heat exchanger.
 
  #39  
Old 03-02-08, 03:02 PM
Member
Thread Starter
Join Date: Jan 2006
Location: south Alabama
Posts: 73
Re:

Once again, thanks for your help pflor!..

I'll try your suggestion out in a bit..

However, I was wondering if carbon monoxide would be leaking through a crack in the heat exchanger (and into the house air) as well (if a crack is indeed the culprit in this case)..

Also, I read another thread somewhere today where someone suggested that one could also hold a lit candle up close to the burners (while they are either coming on or currently operating) and that if the candle flame moves at all then it would be an indication of rollout....would this really work?

Thanks once again!
 
  #40  
Old 03-02-08, 05:58 PM
pflor's Avatar
Member
Join Date: Dec 2007
Location: U.S.A.
Posts: 1,127
A dangerous level of Carbon Monoxide (CO) develops when the burners do not have sufficient air for combustion. Your unit is an outdoor packaged system, it has plenty of air for combustion. CO should not be a concern.

Just picture what happens every time we turn on the stove in our kitchens to cook. The ranges have an open flame right in front of our eyes. We have not gotten sick b/c of them, have we?
 
Reply

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
Display Modes