How to troubleshoot gas furnace? It's not the hot surface igniter...

Reply

  #1  
Old 10-31-12, 07:03 AM
Member
Thread Starter
Join Date: Oct 2012
Location: us
Posts: 17
Received 0 Votes on 0 Posts
How to troubleshoot gas furnace? It's not the hot surface igniter...

Hi everyone. I'm new to this forum, and glad such a forum exists.

Gas furnace stopped working. Blower works, but no flame. I have replaced the hot surface igniter twice in the last 2 years, on this 10 year-old furnace, and that fixed it before. Not this time. LED code 13.

Here's info that may be helpful:

Brand: Carrier

Model number: 58PAV990-14

Age: 10 years in service (8 with no problems)

LED Code: blinking 13

Symptoms: I hear a click, but hot surface igniter never even starts to glow. I replaced with a new one (which has fixed it twice before), and still, no glow at all from the igniter.

LED Code 13 text says: "Limit or flame rollout switch lockout-control will auto reset after three hours. Reset switch or replace fuse link. Refer to #33"
(I can type out #33 if someone needs it)

I tried again after 3 hours with no change.

What I have tried so far: shut off the thermostat (electronic, siitched from HEAT to OFF), flipped the toggle switch inside the furnace (gas valve switch?) to OFF, replaced the hot surface igniter, moved switch back to ON, switched thermostat to HEAT. Blower fan fires up, but no glow at all (not even momentary) in the hot surface igniter.

I'm a complete novice, but will try to fix just about anything that's broken. I may need more specific instructions than someone familiar with furnace parts. I'm not even sure where the "Flame rollout switch" is. Tried to download a manual from online source, but the file was corrupt.

So, can someone help me troubleshoot this? I have a multi-meter, in case I need to check voltages anywhere in the system.

Thanks in advance for any help! Getting chilly in Duluth, MN!

Dennis
 
Sponsored Links
  #2  
Old 10-31-12, 09:24 AM
Forum Topic Moderator
Join Date: Oct 2002
Location: Hamilton County, Ohio
Posts: 4,296
Received 2 Votes on 2 Posts
I could not find your exact model, but this may be close. Check the manual limit switches which should be close to the burners. They should be a push to reset type.

http://www.docs.hvacpartners.com/idc...t/OM58-131.pdf
 
  #3  
Old 10-31-12, 09:58 AM
Member
Join Date: Nov 2007
Location: MI
Posts: 2,612
Received 0 Votes on 0 Posts
Did the error LED go out when you turned off the power? If not then turn it off at the breaker panel. I don't understand why the furnace would even start the blower if the limit has tripped. If you hear a click after the blower is running it sounds like the control board is trying to light the ignitor. If you've replaced the ignitor yourself then you know where the wires are. Take your meter, set to AC volts, and probe the terminals where the ignitor connects on the control board. When you hear that click after the blower starts the meter should indicate 120V. If it does, then you may have a bad ignitor.
 
  #4  
Old 10-31-12, 02:50 PM
user 10's Avatar
Member
Join Date: Mar 2004
Location: NA
Posts: 1,905
Received 23 Votes on 18 Posts
Disconnect the main limit switch and check it for continuity...



The resistance should be near zero ohms if it's closed.

Insufficient airflow can cause the limit switch to open, but it should reset automatically.

The fusible link or rollout switch(s) should be near the burner openings. Rollouts don't trip for no reason, so if it's open, you should call a technician in to pull the blower and inspect the heat exchanger for cracks.
 
  #5  
Old 10-31-12, 03:04 PM
user 10's Avatar
Member
Join Date: Mar 2004
Location: NA
Posts: 1,905
Received 23 Votes on 18 Posts
"I don't understand why the furnace would even start the blower if the limit has tripped."

To cool down the furnace so that the limit resets.
 
  #6  
Old 10-31-12, 07:14 PM
Member
Thread Starter
Join Date: Oct 2012
Location: us
Posts: 17
Received 0 Votes on 0 Posts
Thank you all. It was a crazy day, and I was not able to get back to this, but will first thing tomorrow.

Dennis
 
  #7  
Old 11-01-12, 01:27 PM
Member
Thread Starter
Join Date: Oct 2012
Location: us
Posts: 17
Received 0 Votes on 0 Posts
Thanks to all for the help, I combined my replies to each of you in this one reply.

-Dennis

Originally Posted by muggle
Disconnect the main limit switch and check it for continuity...
I disconnected the main limit switch, and get no reading on the contacts. So, it is open. Stuck open, I presume. So, it this part probably the whole problem (it is a 10 year old part, in an area with long winters), or is this a part that typically goes bad when there is another problem? For $25 I'm thinking of just buying a new one, unless someone tells me it will simply burn out (get stuck open) immediately (because of another problem in-line.)

Originally Posted by muggle
The fusible link or rollout switch(s) should be near the burner openings.
The only thing I see near a burner opening is a flame sensor.

I can take photos and post them, if necessary.

=============================

Originally Posted by guy48065
Did the error LED go out when you turned off the power?
Yes, the LED stops blinking when power is turned off. I also tried shutting off power at the breaker, and when power is reapplied, the LEDs blink the same sequence (code 13.)

Originally Posted by guy48065
If you hear a click after the blower is running it sounds like the control board is trying to light the ignitor. If you've replaced the ignitor yourself then you know where the wires are. Take your meter, set to AC volts, and probe the terminals where the ignitor connects on the control board. When you hear that click after the blower starts the meter should indicate 120V. If it does, then you may have a bad ignitor.
I tried checking for voltage after the "click", both by unplugging the hot surface igniter's plug/clip and checking there (at the feed wires), and also back at the printed circuit board where there is a plug-in for those wires. Result: No voltage.

=========================

Originally Posted by goldstar
Check the manual limit switches which should be close to the burners. They should be a push to reset type.
Unless I'm blind, there are no switches of any sort near the burners. If all furnaces have manual limit switches, they are extremely well hidden in the Carrier 58PAV990
 
  #8  
Old 11-01-12, 02:44 PM
SeattlePioneer's Avatar
Banned. Rule And/Or Policy Violation
Join Date: Jul 2007
Location: Seattle, Wa
Posts: 5,503
Received 0 Votes on 0 Posts
If the limit switch were open, you'd have 24 VAC on one wire going to the limit switch and zero VAC on the other wire connected to the limit switch.


Describe in detail how your tested the limit switch.

The manual on your furnace is at

http://www.xpedio.carrier.com/idc/gr.../58p,r-9sm.pdf

In figure 6, page 4 the location of the manual reset limit switches are shown, located above the burners.

In Figure 12, page 8 is a wiring diagram for the furnace. Two manual reset limit switches are shown all in series with the main limit which resets by itself. So from the main limit you should be able to track the wires to the two manual reset limit switches.

Se if you can identify those parts, and report back on how you tested the limit switch.
 

Last edited by SeattlePioneer; 11-01-12 at 02:59 PM.
  #9  
Old 11-01-12, 03:45 PM
user 10's Avatar
Member
Join Date: Mar 2004
Location: NA
Posts: 1,905
Received 23 Votes on 18 Posts
deleted..........................................
 
  #10  
Old 11-01-12, 05:49 PM
Member
Thread Starter
Join Date: Oct 2012
Location: us
Posts: 17
Received 0 Votes on 0 Posts
Thanks SeattlePioneer,

We're getting closer to finding the correct manual, but that one is not it (or I hope they have another that is specific to this model.) Back in my first post, I mentioned it is a 58PAV990-14, and I assume the "-14" is significant, because the components are different and the wiring diagram is not the same as the one pasted on the inside of the furnace door.

{edit} correct model number is 58PAV090-14

First, I'll answer the question of how I tested the limit switch, then I will post photos of my furnace guts.

Testing procedure for limit switch:
As muggle recommended, I disconnected (removed the two wires connected to) the limit switch. Then, with my multimeter set to the lowest Ohm setting (which happens to be 200 Ω), I touched one probe to each of the connectors. No change in the readout, indicating the switch is open. To test that the multimeter is working properly, touching the probe leads together reads about 0.04Ω.

I also took the limit switch out of the furnace, to visually inspect it. Nothing obvious (physical) was wrong, it had a very minor amount of fine dust so I dusted it off with a soft dry brush.

OK, I'll post this, then get the images ready for upload. As I said, if there is a manual switch, I cannot find it.

Thanks!

Dennis
{edit} correct model number is 58PAV090-14, not 58PAV990-14
 

Last edited by dtleahy; 11-01-12 at 06:49 PM.
  #11  
Old 11-01-12, 06:40 PM
Member
Join Date: Nov 2007
Location: MI
Posts: 2,612
Received 0 Votes on 0 Posts
Jumper across the open limit switch & see if the code stops blinking & furnace lights.
Then of course remove the power until a correct replacement is installed ;-)
 
  #12  
Old 11-01-12, 07:07 PM
Member
Thread Starter
Join Date: Oct 2012
Location: us
Posts: 17
Received 0 Votes on 0 Posts
Thanks, guy48065

The code does stop blinking when I jumper across the wires that lead to the open limit switch.

When I then power up the furnace, there's the "click" then,...

The hot surface igniter does not glow. (and thermostat is set to HEAT and set to a temperature at least 6 degrees above ambient.)

So, I pulled the connector plug off of the hot surface igniter's power wires, and checked for 110VAC on those leads, and get nothing (0.00)

Dennis
 

Last edited by dtleahy; 11-01-12 at 09:18 PM.
  #13  
Old 11-01-12, 08:01 PM
Member
Thread Starter
Join Date: Oct 2012
Location: us
Posts: 17
Received 0 Votes on 0 Posts
Here are a few pictures in the Carrier 58PAV090-14 interior. This is an updraft furnace, blower motor on the bottom.


This is a shot of the furnace, focusing on the area where any manual switches might be. Shot from an upper angle, looking down
==============================


This is a shot of the furnace under the burners, shooting up, from the floor. You can see one white wire at burner #1, which is the flame detector. You can just barely see two wires on the lower right that lead to the hot surface igniter.
==============================



Similar to the first shot, but focusing on the area that was hidden by the gas pipe.
==============================


I also shot the schematic pasted to the inside of the furnace door (and close-ups, so it can be read), if anyone needs/wants it posted. I figured I'd keep the clutter to a minimum.

Thanks!

Dennis
 
  #14  
Old 11-01-12, 11:21 PM
SeattlePioneer's Avatar
Banned. Rule And/Or Policy Violation
Join Date: Jul 2007
Location: Seattle, Wa
Posts: 5,503
Received 0 Votes on 0 Posts
All right --- here's another manual:

http://www.alltemp-hvac.com/58pa-15si.pdf

the 58 PAV is the basic model number.

The 090 is the approximate burner input based on a BTU input of 22,000 BTUs per burner. So your 58PAV 090 has four burners.

the 14 is a series number that describes the way a certain number of furnaces were built.

The manual above is for series 160 furnaces, which I'm supposing were built after your furnace.

Your upflow furnace should have a red wire going to the main limit switch, then a red wire from the other side of the limit switch to a fusible link, and then going to a manual reset flame limit switch.

In your middle picture, the fusible link appears just below the red and white wires to the right of the burners.


What parts are connected by the wires from the limit switch and fusible link? There should be a resettable limit switch connected in there.


See if you can make sense of things from that description.
 
  #15  
Old 11-02-12, 05:49 AM
Member
Thread Starter
Join Date: Oct 2012
Location: us
Posts: 17
Received 0 Votes on 0 Posts
Thanks, SeattlePioneer,

The 2 red wires going to the main limit switch have no connections in the upper compartment, but trace directly to the PC board (in the blower compartment.) I can post a photo of the PC board and a few photos of the wiring diagram if that would help. I see no switches on the PC board, but will look again for switches.

Dennis
 
  #16  
Old 11-02-12, 07:08 AM
Member
Thread Starter
Join Date: Oct 2012
Location: us
Posts: 17
Received 0 Votes on 0 Posts
(http://www.alltemp-hvac.com/58pa-15si.pdf)

This manual may show a diagram that is the functional equivalent of my model, but the diagram and schematic are different. Also, the manual mentions to the installer to be sure to "verify manual reset switches have continuity" in the checklist, but again, I do not think my model has a manual reset switch.

The only manual switches I see in the entire furnace are:
1.) the toggle ON/OFF switch on the gas valve
2.) the switch on the furnace housing to indicate that the cover is on
3.) (I think it is a ) "blocked valve" switch - and it does have a manual reset switch which I have tried pressing (can suppy photo if needed)

There is (evidently) another automatic switch which is a "pressure switch." (It is mentioned in some of the Carrier manuals I've looked at.

=============================

Here is the diagram + schematic from my furnace:


And here is a link to that image file, in case the forum software has made it too small: http://www.LeahyGuitars.com/Imagez/T...8PAV090-14.jpg

Dennis
 
  #17  
Old 11-02-12, 07:51 AM
Member
Thread Starter
Join Date: Oct 2012
Location: us
Posts: 17
Received 0 Votes on 0 Posts
I may be adding more pictures, and confusing the issue - and apologize if that is true.

Here is another image of the top compartment showing the switches I mentioned in post #16.



The "blocked valve" switch I believe is at the top, with 2 orange wires leading to it. There is a small brown, pushbutton switch between the connectors.

The pressure switch is the 1-1/2 round component, inline with the blocked valve switch.

Dennis
 
  #18  
Old 11-02-12, 09:24 AM
SeattlePioneer's Avatar
Banned. Rule And/Or Policy Violation
Join Date: Jul 2007
Location: Seattle, Wa
Posts: 5,503
Received 0 Votes on 0 Posts
Well, if there are no other parts connected to the main limit switch, then there aren't, I suppose.


The circuit diagram YOU PROVIDED shows the circuit in question between connections 1 and 7 connecting Flame rollout switch 1 (FRS1) flame rollout switch 2 (FRS2), the fusible link (FL) and the main limit Switch (LS).

The fusible link is shown in your earlier pictures. It's in the middle picture just below the red and white wires, and looks like two small blobs of brown with a wire connecting them, the wire being the fusible link that melts if hit by flame.

So what is the fusible link connected to?

Does the limit switch you tested look like that pictured by Muggle?
 

Last edited by SeattlePioneer; 11-02-12 at 10:21 AM.
  #19  
Old 11-02-12, 09:40 AM
Member
Join Date: Nov 2007
Location: MI
Posts: 2,612
Received 0 Votes on 0 Posts
On my furnace when the thermostat calls for heat a relay closes & the inducer motor spins up. Pressure in the inducer housing closes the sail (pressure) switch and the ignitor lights with a "click". After a couple seconds the gas valve opens. Once the heat exchanger is hot the last relay closes & the blower starts.

I'm hung up on "click" but no ignitor. Is it the right click? Other limits, inducer motor sail switch (your "pressure switch") and such would need to be closed for the CPU to activate the ignitor--but all those switches can't normally be heard. The ignitor relay makes a loud click and it's activated directly by the CPU. No other switches or interlocks are in-line to the ignitor.

Here's what I would do:
See if the PCB has the relays labeled like on the schematic & pull the HSI relay. There now should be no click. If it's the same type, swap the HSI and BLWR relays. See if the click now lights the ignitor. Let it go until the gas valve opens & the burners light, then shut it all off because, as I suspect, your ignitor relay is bad and it's now controlling the blower. No blower = overtemp.
 
  #20  
Old 11-02-12, 10:21 AM
SeattlePioneer's Avatar
Banned. Rule And/Or Policy Violation
Join Date: Jul 2007
Location: Seattle, Wa
Posts: 5,503
Received 0 Votes on 0 Posts
Hello Guy,


You are providing poor advice in my opinion. It's apparent that dtleahy has limited electrical skills and knowledge and your advice to start plucking out relays and changing them when the diagnostic work on the furnace hasn't been completed is a bad idea, in my opinion.
 
  #21  
Old 11-02-12, 10:29 AM
user 10's Avatar
Member
Join Date: Mar 2004
Location: NA
Posts: 1,905
Received 23 Votes on 18 Posts
Temporarily bypass the temperature limit as shown in the pic I posted (do not bypass anything else; It's very dangerous to do so) and turn on the furnace.

If it fires off check the temperature rise.

Allow the furnace to run for 10 minutes and measure the temperature (in Fahrenheit) in the return drop and supply trunk line. (measuring right above the furnace isn't accurate)

The supply/return temperature difference shouldn't be outside the range printed on the rating plate.

If the limit is bad, yet the temp rise is okay, replace it - the new one has to have identical ratings.

If the temp rise is too high, change the filter and make sure that all the vents are open. Insufficient airflow can cause the high limit to cycle the furnace, resulting in failure; it may have been tripping the limit since day one.

The following can cause insufficient airflow...

- Block filter, dirty blower wheel, closed vents
- Dirty evaporator coil
- Use of dense allergen-reduction filters
- Furnace overfired - burning too much gas
- Incorrect blower speed for the application (see point below, under normal circumstances, factory setting should be fine)
- Undersized ductwork

Warning:

Do not operate furnace for heat with high limit bypassed. A having a furnace overheat due to a bypassed limit can cause a house fire or worse. Follow the above instructions at your own risk.
 
  #22  
Old 11-02-12, 10:39 AM
user 10's Avatar
Member
Join Date: Mar 2004
Location: NA
Posts: 1,905
Received 23 Votes on 18 Posts
See if the PCB has the relays labeled like on the schematic & pull the HSI relay. There now should be no click. If it's the same type, swap the HSI and BLWR relays. See if the click now lights the ignitor. Let it go until the gas valve opens & the burners light, then shut it all off because, as I suspect, your ignitor relay is bad and it's now controlling the blower. No blower = overtemp.
It's already apparent that the high limit switch is stuck open.

If something is wrong with the board, the entire board should be replaced, not repaired. (for safety reasons)
 
  #23  
Old 11-02-12, 10:50 AM
Member
Thread Starter
Join Date: Oct 2012
Location: us
Posts: 17
Received 0 Votes on 0 Posts
Originally Posted by SeattlePioneer
Well, if there are no other parts connected to the main limit switch, then there aren't, I suppose.
...
The circuit diagram YOU PROVIDED shows the circuit in question between connections 1 and 7 connecting Flame rollout switch 1 (FRS1) flame rollout switch 2 (FRS2), the fusible link (FL) and the main limit Switch (LS).
...
Does the limit switch you tested look like that picrtured by Muggle?
I see that the diagram says there may be a FRS1 and FRS2, but note that it says "when used", and evidently this time they did not.

A clarification from earlier is that there is a small component (not a switch) in-line in one of the red wires that go all the way from the main limit switch to the PC board. About the size of a large resister or diode. That is evidently the (FL) fusable link. I took the main limit switch back out, and photographed it with the red wires connected, which shows the fusable link.


And yes, it looks just like the main limit switch pictured by muggle.



The fusible link is shown in your earlier pictures. It's in the middle picture just below the red and white wires, and looks like two small blobs of brown with a wire connecting them, the wire being the fusible link that melts if hit by flame.

So what is the fusible link connected to?
I hope I phrased my previous wording correctly (sorry if I'm making this more difficult than it should be.) I'm not sure what you are seeing in the other photo, but there is nothing else in-line on the red wires leading from the main limit switch (except, as noted, the fusable link that is in-line right at the connector.) Other than that little component, the red wires go all the way down to the PC board (to the "PL1" connector block, on pins 1 and 7.)

Dennis
 
  #24  
Old 11-02-12, 11:41 AM
SeattlePioneer's Avatar
Banned. Rule And/Or Policy Violation
Join Date: Jul 2007
Location: Seattle, Wa
Posts: 5,503
Received 0 Votes on 0 Posts
Yes, that's the fusible link connected to the limit switch. Do a continuity check on that with your meter to see if that is an open circuit (blown) or a continuous circuit through the limit switch.


If the heat exchanger gets plugged, the burner flames will back out of the heat exchanger into the burner compartment and start burning up the wires. The fusible link is very sensitive to flames and will shut off the burners if that happens.


<< I hope I phrased my previous wording correctly (sorry if I'm making this more difficult than it should be.) I'm not sure what you are seeing in the other photo, but there is nothing else in-line on the red wires leading from the main limit switch (except, as noted, the fusable link that is in-line right at the connector.) Other than that little component, the red wires go all the way down to the PC board (to the "PL1" connector block, on pins 1 and 7.)
>>


OK.
 
  #25  
Old 11-02-12, 12:06 PM
Member
Thread Starter
Join Date: Oct 2012
Location: us
Posts: 17
Received 0 Votes on 0 Posts
Hi Muggle,

Originally Posted by muggle
Temporarily bypass the temperature limit as shown in the pic I posted (do not bypass anything else; It's very dangerous to do so) and turn on the furnace.

If it fires off check the temperature rise.

Allow the furnace to run for 10 minutes and measure the temperature (in Fahrenheit) in the return drop and supply trunk line. (measuring right above the furnace isn't accurate)

The supply/return temperature difference shouldn't be outside the range printed on the rating plate.

If the limit is bad, yet the temp rise is okay, replace it - the new one has to have identical ratings.

If the temp rise is too high, change the filter and make sure that all the vents are open. Insufficient airflow can cause the high limit to cycle the furnace, resulting in failure; it may have been tripping the limit since day one.

The following can cause insufficient airflow...

- Block filter, dirty blower wheel, closed vents
- Dirty evaporator coil
- Use of dense allergen-reduction filters
- Furnace overfired - burning too much gas
- Incorrect blower speed for the application (see point below, under normal circumstances, factory setting should be fine)
- Undersized ductwork

Warning:

Do not operate furnace for heat with high limit bypassed. A having a furnace overheat due to a bypassed limit can cause a house fire or worse. Follow the above instructions at your own risk.
Yesterday, I did try bypassing the main limit switch. (I connected the two red wires with a piece of 14ga jacketed solid copper wire with ends stripped and pounded flat so they could go into the connectors.) That does mean that I was also counting on the fusable link being OK. It seems completely intact, no indication of failure - would I know visually? I can bypass that as well and try again, but my attempt yesterday ended with me measuring zero volts on the wires leading to the hot surface igniter.

Assuming I get to the point where the furnace even fires up, I will have to buy a thermometer that I can use to measure temperatures in the supply and return ductwork. Will one of those non-contact infrared types that you aim like a gun work for this process? (I would not mind owning one of those anyway), or do I need to buy a special thermometer?

So, if I try again, bypassing the main limit switch (temporarily), and the hot surface igniter does not glow, and there is no voltage being supplied to the sot surface igniter wires (after the audible "click"), then what is the next step in troubleshooting?

I don't doubt that the blower is dirty, but would any of the symptoms of dust accumulation in the system keep the unit from even firing up at all? I guess I would expect it to fire up, then shut itself off if some sort of airflow problem would have suddenly developed (or even hit a threshold.) Am I thinking clearly on that point, or showing a lack of understanding on the process?

  • the furnace has worked for 10 years
  • the blower has been (pretty much) running continuously for 10 years (and still works)
  • there have been no ductwork changes ever
  • all vents are open
  • the previous filter was only moderately dirty (they are changed frequently)
  • there is a new filter in the furnace, not the outrageously thick allergen filters, but pleated white "paper" with a Merv 8 rating.

I realize the furnace runs a sequence, sort of self-diagnosis, as it starts up. So, for example, the gas valve never opens if the hot surface igniter doesn't fire up. It seems like something is keeping the hot surface igniter from receiving voltage, so what else besides the main limit switch would prevent it?

Hi SeattlePioneer,

Originally Posted by SeattlePioneer
Yes, that's the fusible link connected to the limit switch. Do a continuity check on that with your meter to see if that is an open circuit (blown) or a continuous circuit through the limit switch.
OK, it tests as working (shows continuity.)

Dennis
 
  #26  
Old 11-02-12, 01:05 PM
SeattlePioneer's Avatar
Banned. Rule And/Or Policy Violation
Join Date: Jul 2007
Location: Seattle, Wa
Posts: 5,503
Received 0 Votes on 0 Posts
Your test of continuity through the fusible link proves that part is OK.

Your test of the limit switch with that being an open circuit proves that part is defective and should be replaced.


Is the inducer motor switching on when the thermostat calls for heat and staying on when you bypass the limit switch?
 
  #27  
Old 11-02-12, 02:14 PM
Member
Thread Starter
Join Date: Oct 2012
Location: us
Posts: 17
Received 0 Votes on 0 Posts
Originally Posted by SeattlePioneer
Your test of the limit switch with that being an open circuit proves that part is defective and should be replaced.
So, that part is bad. I just ran out and bought one. Just to make sure I tested the old part correctly, I repeated the test and tested the new one. Old was was open; new one closed.

Is there a chance I'll just fry the new part, if something else is wrong? In other words, should I wait before installing that new part, and just bypass it for now, until all other troubleshooting is done?

Dennis

I spoke briefly to a service tech who wondered if I was really seeing "13" or was I seeing "31" for the LED code, and I'm going to look at that again.
 
  #28  
Old 11-02-12, 03:00 PM
SeattlePioneer's Avatar
Banned. Rule And/Or Policy Violation
Join Date: Jul 2007
Location: Seattle, Wa
Posts: 5,503
Received 0 Votes on 0 Posts
Go ahead and replace the part. There is no danger of damaging it.


The diagnostic code you observed was correctly indicating that the limit switch was open. I see no reason to suppose you were interpreting it incorrectly.

One you have the new part installed, start the furnace and let's see how far it gets in the sequence of operation.

You may get a new diagnostic code if the HSI doesn't warm up.
 
  #29  
Old 11-02-12, 04:28 PM
user 10's Avatar
Member
Join Date: Mar 2004
Location: NA
Posts: 1,905
Received 23 Votes on 18 Posts
The thermometer has to have a stem which can be inserted into the ductwork.



Infrared thermometers probably aren't very accurate.
 
  #30  
Old 11-02-12, 06:18 PM
Member
Thread Starter
Join Date: Oct 2012
Location: us
Posts: 17
Received 0 Votes on 0 Posts
With the replacement limit switch installed, the LED code changes to 12.

Dennis
 
  #31  
Old 11-02-12, 06:31 PM
SeattlePioneer's Avatar
Banned. Rule And/Or Policy Violation
Join Date: Jul 2007
Location: Seattle, Wa
Posts: 5,503
Received 0 Votes on 0 Posts
The fan circulating air around the house should run for 90 seconds with that code when the furnace starts up. Let it run and report what happens.
 
  #32  
Old 11-02-12, 06:31 PM
user 10's Avatar
Member
Join Date: Mar 2004
Location: NA
Posts: 1,905
Received 23 Votes on 18 Posts
"14, and I assume the "-14" is significant, because the components are different and the wiring diagram is not the same as the one pasted on the inside of the furnace door."

The 14 indicates the amount of airflow the furnace is designed to move at a specific duct pressure.

14 is short for 1400 cubic feet per minute.

The blower size is important for a/c. (1400 cfm -> up to 3.5 ton a/c can be used)

----------------------
Code 12 indicates that a call for heat was present when you turned the power back on. Blower should run for 90 seconds. (from page 9 of http://www.xpedio.carrier.com/idc/gr.../58p,r-9sm.pdf)

After 90 seconds, it should resume normal operation.
 
  #33  
Old 11-02-12, 06:53 PM
Member
Thread Starter
Join Date: Oct 2012
Location: us
Posts: 17
Received 0 Votes on 0 Posts
JOY IN MUDVILLE!

I went through the sequence again, starting with flipping the breaker. I was checking voltage at the gas valve, and the hot surface igniter started glowing...

It has been running for half an hour, so I do believe it was just the limit switch.

Huge thanks to each of you for taking the time to help.

Heat!

Dennis
 
  #34  
Old 11-02-12, 11:27 PM
Member
Join Date: Nov 2007
Location: MI
Posts: 2,612
Received 0 Votes on 0 Posts
Good job Dennis! I'm still scratching my head why it worked with the new limit installed but not with a jumper...Was it just a matter of giving it enough time (90 seconds) to "do its thing"?
 
  #35  
Old 11-03-12, 05:05 AM
Member
Thread Starter
Join Date: Oct 2012
Location: us
Posts: 17
Received 0 Votes on 0 Posts
Hi guy48065,

Unless there was some sort of 'lockout' going on that was reset by shutting off the gas switch and/or power at the breaker after installing the new limit switch, or by just waiting a length of time for automatic reset, I'd have to admit that the most likely thing was not waiting the full 90 seconds in my testing.

The only other thing I did was to note that there is a small piece of rubber tubing leading from the pressure switch back into the ductwork, and I examined it, (blindly) with fingertips, checking to see if it seemed dry or obviously cracked, and I did squeeze that tube several times (which could have dislodged something partially blocking that switch.) I'd say that is a long shot, and realistically I probably was not waiting the full 90 seconds when I was bypassing the limit switch (which I checked at least twice, once with the HSI plugged in and once unplugged to see if the wires were supplying voltage.

Each time I have worked on the furnace, I have learned a lot, and really appreciate goldstar, guy48065, Muggle, and SeattlePioneer hanging in there with this furnace newbie until it was fixed.

Dennis
 
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
 
Ask a Question
Question Title:
Description:
Your question will be posted in: