Prog Thermostat Problem Stumped Me

Reply

  #1  
Old 10-21-04, 07:03 PM
Holtz
Visiting Guest
Posts: n/a
Question Prog Thermostat Problem

Okay so I consider myself a fairly handy guy, but this has me stumped.
I am switching my 30 yr old Furnasman gas forced air with A/C's thermostat to a Honeywell ct3500. The A/C was installed after the origonal furnace. I am sure the wires are correct but is as follows and I traced it back to the furnace to verify correct origonal wiring.
White on gas valve from furnace to W on thermostat
Black on G on furnace to G on thermostat
Black on R on furnace to RC on thermostat with a jumper to R
Red on Y on furnace to Y on thermostat
Problem is this,,, everything works on the thermostat, leds, time, temp, heat signal, along with the little flame to show it has signaled the furnace to start, but nothing happens with the furnace. Flick the manual fan switch to on and still nothing happens. Called Honeywell help line,,, and no help he did not know.
I believe that the furnace is 24 volt but my meter does not show any coming out of the wires.
Anybody ?????
 

Last edited by Holtz; 10-23-04 at 07:02 AM.
Sponsored Links
  #2  
Old 10-24-04, 08:58 AM
Sharp Advice's Avatar
Admin Emeritus
Join Date: Feb 1998
Location: The Shake and Bake State USA
Posts: 10,440
Upvotes: 0
Received 5 Votes on 4 Posts
Hello: Holtz

Anybody (myself) is about to take a crack at helping you. Don't expect too much. Many possible variations are likely to exist. Text only help may not be sufficient to solve the problem(s).

If there is no transformer voltage at the thermostat, the thermostat is not wired correctly in series with the gas valve, the transformer and any safety device the furnace has installed on it.

That says plenty in general but nothing really specific granted. Depending upon what safety devices there are on that specific furnace and how it was currently wire determines how the new thermostat gets connected.

Since the furnace is 30 or so years old, doubt the is any safety devices installed. But thought I would mention so for benefit of any other readers and to may that consideration forfront and inclusive of basic T-Stat installations. Not all are alike. Varies based upon each furnace. No standarized methods or wire colors often used back than.

With the installation of the A/C unit after the original furnace installation, the wiring colors are likely to have been changed. Follow the wires from the transformer. One should go directly to the gas valve. The other terminal on the gas control should have a wire to the T-Stat.

Or the gas control may have a four wire terminal. One from T-Stat, one from transformer, one from pilot safety system and one back to T-Stat or in some fashion such as that. Power from transformer must be at gas control valve and at red wire on T-Stat.

White wire from T-Stat back to gas control valve or though a remote seperate unit pilot safety device. Which may be a pilot generator (PG) safety element or thermocouple (TC) in the pilot assembly or safety element of the PG through a Basso Auto Safety Pilot Shut Off device, etc.

Furnace may not even have any transformer current to T-Stat, if furnace has a PG. The PG supplies the current to T-Stat and gas control. Many such furnaces used the PG as the current to operate T-Stat and gas control valve.

Plenty of variations which may or may nor apply. Mat be one of several reasons the T-Stat manufacturer could not offer any over the phone verbal help. Only on site help from a tech can solve the problem or that T-Stat is not designed and or intended to be used on that furnnace with those types of DC non transformer current supplied systems, etc.
 
  #3  
Old 10-24-04, 10:54 AM
Ed Imeduc's Avatar
Member
Join Date: Aug 2002
Location: Mountain Williams Missouri
Posts: 18,389
Upvotes: 0
Received 0 Votes on 0 Posts
Wink

Black on G on furnace to G on thermostat
Black on R on furnace to RC on thermostat with a jumper to R
This we cant have two blacks. When you check for 24V check at the transformer. I take it the tstat has batt. in it that is why it works.
Now all tstats are about the same dont havre paper on the ct35 but on the ct 36 so try this .
R is power
Rh is heat transformer
Rc is cool transformer
W heat load
Y is compressor
G is fan
W2 is 2nd stage heat
Y2 2nd stage cool
C is common

The R or the power comeing up from the furnace you have to put a jumper on from R to Rh to Rc
If you just jump the G to one of the blacks and thee fan comes on it should show you what one is the hot.

ED
 
  #4  
Old 10-24-04, 02:35 PM
Holtz
Visiting Guest
Posts: n/a
Hey guys I reviewed comments and looked in the furnace again. Wire color does not bother me,I know some are the same but I can see where they go to.
From the gas valve one white goes to the t stat the other goes to what looks like a transformer mounted on the side of the furnace. It says relay fan centre with some numbers and diagram on it, it has on the side a y and w for connections, and it is also mounted to another box which has a switch on top with terminals r,g,c on the side right by the other y and w.
Does this help?
 
  #5  
Old 10-24-04, 03:42 PM
Sharp Advice's Avatar
Admin Emeritus
Join Date: Feb 1998
Location: The Shake and Bake State USA
Posts: 10,440
Upvotes: 0
Received 5 Votes on 4 Posts
Hello: Holtz

Maybe we need to try a diagnostic from another angle.
First need to know some of the basics of that furnace, since the unit is some 30 years old.

Questions:

1)
Does the furnace have a constant burning pilot? Yes or No.
(Helps to establish the type of safety system that furnace has)

2)
Is there a button to hold down to get gas to pilot when manually using match to light a pilot? Yes or No?
(Answer indicates the pilot lights with a match flame and safety system has a thermocouple as the safety shut off device and uses a t-couple not a PG.

OR

3A)
A tiny "B" looking or like valve on gas control valve or from manifold that you have to turn to get pilot gas to the pilot assembly, that must be manually lighted with a match?

3B)
Meaning pilot would be a constant burning (always on) pilot and pilot flame lit with a match? Yes or No (Indicates a PG pilot safety system)

3C)
If the answer to 3A is yes, safety system is a PG system. (3B)
Some PG's operated the T-Stat and gas control. Older furnaces still had a fan relay (120 volt) which may be mounted outside, which only operated the blower fan when the firebox temp reached set temp. Ot box is or could be the main power (120 volt) switch OR the manual turn on for the fan motor.

If the system has a Basso valve (maybe on the side of furnace or inside under front removeable cover) and one or two wires from PG go to it, than there is a button on the device to push to reset safety device.

"Basso" valves are the burner only shut off safety devices used to shut off only burner gas if PG died, gas to pilot flame fails or is shut off or pilot blows out, etc.

If the system uses a PG pilot, may be the ring is on the bottom of the gas control valve or one of those boxes on the side of the furnace you mentioned or on the inside front of the furnace.

Once the basics are known, more likely to better determine problem cause and solution. Still thinking the system does not use AC current to T-Stat or may not. T-Stat on do to batteries installed into it. Or not the correct T-Stat for the system. May need a Millivolt T-Stat....????

Hope the above is well explained and described. Clearer than mudd hopefully. Difficult to determine problem cause without the basics being known and equally as difficult to explain a possible solution. (IMO)
 

Last edited by Sharp Advice; 10-24-04 at 03:54 PM.
  #6  
Old 10-24-04, 04:37 PM
Holtz
Visiting Guest
Posts: n/a
Hi thanks for replying.
Answers are.
1. yes pilot is always burning.
2.3. To light pilot you have to turn a dial to pilot push down to light then hold for a min or so, then it comes up and then turn it to on position.
Also the box that was referred to does have 120v 60hz on it. Under neath there is a little black box with 2 terminals marked load and line but nothing is hooked to it, which I think may be a small transformer.
Their are a couple of wires coming from the boxes to another box which is the fan switch, it has pull on and push off.
T-stat is on batteries that is why it was working, but not able to run the system.
Does this information work?
Cheers
Holtz
 
  #7  
Old 10-24-04, 05:06 PM
Ed Imeduc's Avatar
Member
Join Date: Aug 2002
Location: Mountain Williams Missouri
Posts: 18,389
Upvotes: 0
Received 0 Votes on 0 Posts
Wink

Found the CT3500 Lay out Its like I said the same. You have to work it out down there by the furnace. pull the blower door off and see if there is a schematic on it . One wire from the transformer R goes to R and jump to Rc. now if you jump from R to the W wire you should have heat. if not look and see WHY W to the gas valve didnt turn on. Is the other wire common from the transformer on the gas valve??. Did you turn the power off when you pull the old tstat off the wall?? Could you have another transformer from the AC unit ,and they use it. Is power off to the AC ?

http://www.shop.store.yahoo.com/air-n-water
Has the layout for that CT3500

ED
 

Last edited by Ed Imeduc; 10-24-04 at 05:20 PM.
  #8  
Old 10-24-04, 05:33 PM
Sharp Advice's Avatar
Admin Emeritus
Join Date: Feb 1998
Location: The Shake and Bake State USA
Posts: 10,440
Upvotes: 0
Received 5 Votes on 4 Posts
Hello: Holtz

Making good progress. Frnace uses a T-Couple and not a PG.

Has a fan switch marked pull on and push off. Manual fan blower switch.

One electrical box is a transformer and other smaller box may be power for doorbell. Doorbell transfomers use to be mounted on the side of some heaters back than and now likely disconnected.

Ed found the Honeywell ct3500 thermostat. Should now be better able to get T-Stat wired up correctly and heater working....

Check voltages out of transformer going to gas control valve. Should be power at transformer and voltage out to gas valve. If not, check electrical power into transformer.
 
  #9  
Old 10-29-04, 11:41 AM
Holtz
Visiting Guest
Posts: n/a
Sorry for the delay I was out of town.
I have some power to one of the terminals going to the gas valve, the other is neutral and the neutral is going up to Tstat.
What now ?
Cheers
Holtz
 
  #10  
Old 10-29-04, 12:28 PM
Ed Imeduc's Avatar
Member
Join Date: Aug 2002
Location: Mountain Williams Missouri
Posts: 18,389
Upvotes: 0
Received 0 Votes on 0 Posts
Wink

jump just R to W does it turn on ,the furnace????


ED
 
  #11  
Old 11-06-04, 12:10 PM
Holtz
Visiting Guest
Posts: n/a
Hi Ed
Sorry nope it does not turn it on.
Cheers
Holtz
 
  #12  
Old 11-06-04, 12:50 PM
Ed Imeduc's Avatar
Member
Join Date: Aug 2002
Location: Mountain Williams Missouri
Posts: 18,389
Upvotes: 0
Received 0 Votes on 0 Posts
Thumbs up

With R to W at the tstat do you read 24V at the gas valve? R to G do you get fan? With the mix up in color you have on the wire there I find some times it helps to sit down and draw it all out. One leg of the transformer is R to the tstat. The other leg is common this has to go to all the things that work in the furnace and AC. This tstat said it works cause of the batteries is all. Hope you get it going.

ED
 
  #13  
Old 11-07-04, 09:37 AM
Holtz
Visiting Guest
Posts: n/a
Sorry Ed yes when I jump r to w it does turn on the furnace as when I performed the task of jumping at the tstat and went to test the volts the burners were fired but fan had not kicked in yet. Yes R to G turns fan on.
I see the R at the furnace and that wire runs up to the tstat r and rc, I also found the C or common which runs to the gas valve, and also to the AC, but also right inbetween the R and C is a G which also runs to the AC, I assume this to be another common? The other wire on the gas valve runs up to the W on the tstat, which makes sense as when the tstat closes the loop to call for heat it turns the furance on.
Only other thing might be the actual volts, as I am a novice and am not sure of the quality of my tester, I cant be sure that 24v is going through the system as my reader does not show anything close to that, all it does is the needle bounces a little when there is power.
Might it be that the transformer may not be putting out enough to run the new tstat but puts out enough to run the existing mechanical one? If so is it an easy thing to put in a new transformer? I have done this before on another application, but this one looks quite different.
Cheers
Holtz
 
  #14  
Old 11-07-04, 12:36 PM
Ed Imeduc's Avatar
Member
Join Date: Aug 2002
Location: Mountain Williams Missouri
Posts: 18,389
Upvotes: 0
Received 0 Votes on 0 Posts
Wink

If you jump R to W at the tstat and you said the furnace came on. OK the fan has to turn on at the furnace when its hot there .So can be up in the tstat. Draw it out ok Common one side of the transformer has to go to the furnace valve the fan relay the outdoor AC unit. The other leg or R goes to the tstat there the tstat can turn the R to the W for heat Y for cool and G for fanWhen set to cool the R will turn on Y and G at the same time.If you want you can put a new transformer in make sure and get a 40 or 50 Va for it

ED
 
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: