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Old 10-17-2005, 12:27 PM   #1
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Furnace does't start when Fan is 'auto'


I recently replaced my old thermostat with a new programmable NOMA 5+1+1 thermostat. This is the first time I am trying to turn the furnace on with the new t-stat and the AC worked fine with it. I followed the manufacture’s recommendation on wiring.
When I put the thermostat to Heat/On position, fan to Auto, and raise the temperature to 80 degrees, room temp was 50 degrees, there was no response from the furnace. The thermostat clicked and “heat” was flushing, which means it was sending a signal to the furnace to kick in, but the furnace would not start. However, when I changed the fan to manual “on”, both the fan and furnace started. When the temperature was reached, the furnace would stop but the fan would go on because it was on ‘on’ instead of “auto”

It is an old
Lennox gas furnace. Would anybody have any idea what could be wrong?

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Old 10-17-2005, 09:41 PM   #2
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Furnace does't start when Fan is 'auto'


Sounds like a bad thermostat. I'm not a HVAC guy but it sounds like the auto setting is the culpret. Check the wiring to be sure you did in fact wire it right first.

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Old 10-18-2005, 07:10 AM   #3
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Furnace does't start when Fan is 'auto'


Quote:
Originally Posted by MinConst
Sounds like a bad thermostat. I'm not a HVAC guy but it sounds like the auto setting is the culpret. Check the wiring to be sure you did in fact wire it right first.
Thanks, you were right. You are not an HVAC guy but certainly you are knowledgeable as one. Even before I got your message, I checked the wires and connected the black wire with red one to ‘R’, and it worked. The black one was connected to ‘G’ for unexplained reason. Eh…
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