Dead thermostat? or furnace issue? - http://www.hvacmechanic.com/ Forums
Original message
| pegglegg007
 |  "Dead thermostat? or furnace issue?"
, posted Mon 28 Apr 16:43  
Issue: (I think)
Thermostat is dead.
Equipment:
Furnace - Lennox forced air furnace (3 years old) with A/C unit
Thermostat - Its a carrier, non programmable, digital readout. It looks just like this one, but isn't programmable:
http://www.lodgingac.carrier.com/Files/LodgingAC/Global/US-en/52CP_TSTAT-PROGRAMMABLEINSTALLATION.PDF
Symptoms:
1. Digital Display isn't working, pushing buttons doesn't appear to do anything
2. The fan is running constantly
3. No heat is coming out
Diagnosis steps taken:
1. I popped the thermostat open and even without any of the prongs being connected to connector plate the fan still runs.
2. Jumpered the R and W/W1 to see if the heat would kick on. It didn't
Since the furnace fan still runs even when the thermostat isn't connected does that mean its probably not the thermostat? or would the furnace "remember" its last setting when the thermostat "died"
Dan
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Replies:
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| Zzz
| "Re(1):Dead thermostat? or furnace issue?" , posted Tue 29 Apr 21:46
Your furnace is out on a limit, they do this as a saftey measure. there are 2 brown wires going into the blower compartmant, check for continuity there with whe plug undone (secondary limit.)On the front of the furnace there is a square 1 1/2" x 3" or so, check for 24v ac there. You can jump these for one cycle just to get warm but stay near the furnace cuz if that one went it's overheating. (primary limit.) You will see some little round silver things on the burner cover with a red button in the middle, push the button. If this dosen't fix your problem you better call a tech.
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| pegglegg007
| "Re(1):Dead thermostat? or furnace issue?" , posted Tue 29 Apr 11:56
The breaker doesn't appear to be tripped, and I don't see any other fuses in line from the transformer.
1. Should I be looking elsewhere for a fuse?
2. How can I check the transformer with a DMM to ensure its not fried?
Dan
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| TnNATE1412
| "Re(1):Dead thermostat? or furnace issue?" , posted Mon 28 Apr 20:10
Most likely you have tripped the low voltage circuit breaker or fuse in the furnace. The furnace blower will run constantly when the low voltage circuit opens to indicate a problem.
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