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I have a Lennox Whisper Heat G20Q3/4E-125-4 furnace.

Customer Question
Yesterday evening we noticed that...
I have a Lennox Whisper Heat G20Q3/4E-125-4 furnace.
Yesterday evening we noticed that the temperature in the house was dropping and the registers were blowing cool air.
The house temperature is now 63 on the thermostat, the thermostat is set to 50 and the fan is continuing to run.
The thermostat is an old, round Honeywell. The fan continues to run regardless if the thermostat is set to heat, cool or off, and whether the fan switch is set to auto or fan.
Before I noticed the fan was running all of the time, I jumped the Red and White terminals on the thermostat base to see if it initiated the firing sequence, but no luck.
I also pulled both panels on the furnace and there are no obvious loose wires and though its hard to see, no obvious burned components on the board.
The damper opens manually, but does not open when I restart the furnace.
Thanks,
Rick
Submitted: 11 months ago.Category: HVAC
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Answered in 3 minutes by:
12/8/2016
HVAC Technician: Brian HVAC Guy, HVAC Technician replied 11 months ago
Brian HVAC Guy
Brian HVAC Guy, HVAC Technician
Category: HVAC
Satisfied Customers: 953
Experience: I have been an HVAC/R mechanic/technician for 30+ years.
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Hi Rick, I'm Brian and I'm here to help! Did you notice if your furnace was displaying fault code through the peek hole on the furnace? This sounds like a limit has tripped. A code will help zero in on the issue. Thanks

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HVAC Technician: Brian HVAC Guy, HVAC Technician replied 11 months ago

Looking at the wiring diagram and reading the sequence, you could be on to something about the damper though. The damper proof switch is in the same circuit at the rollout switch and the blocked vent switch and the fan would run continuously if any of those weren't met. The damper motor is the first thing to energize on a call for heat. If the damper isn't moving then I would say either the damper blade is too tight for the damper motor to overcome or the damper motor itself has failed. If you can open the damper manually and the furnace starts, then all the other safeties in the circuit are good and it's probably the damper motor itself. The damper motor is energized through the control board so there's a possibility there is an issue with the relay that energizes the damper too. Testing for voltage at the damper motor or across the damper motor relay contacts is the only way to determine for sure what's going on. Let me know if you have a meter and would like help testing.

Thanks,

Brian

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Brian HVAC Guy
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