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Old 02-07-2010, 01:35 PM   #1
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Furnace fan runs all the time

I have a Lennox heat pump and gas furnace. I replaced an old mercury thermostat with a Honeywell rth3100c1002 digital non programable thermostat. The fan is set to auto but runs all the time. If I lower the temp setting by 1 degree it will shut off, then I can raise it back and it will stay off until the furnace turns on again, then it stays on. I have rechecked the wiring charts and it is wired correctly. Is there a setting for this or is it just a defective thermostat?

Also, the fan turns on as soon as it calls for heat, is this normal with heat pumps? The old thermostat did the same thing.



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Old 02-07-2010, 08:44 PM   #2
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It sounds like your have the Fan wire on the wrong terminal.


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Old 05-13-2011, 05:07 PM   #3
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We did the same switch on the thermostat. went from mercury to programmable. seemed to work on ac/heat but fan never turned off. Then had to replace blower motor now all it does is fan runs all the time. this is a heat pump system and there are four wires to thermostat and another not used. Wasn't used on mercury switch. Wiring going back to unit doesn't seem to match but wrote down where all wires came from thermostat.
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Old 05-13-2011, 05:32 PM   #4
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So what are the wires hooked to? I'm used to r,c,g,y,o,w and e connections on a heat pump thermostat. Maybe one of the other guys knows how to make it work with 4 wires.
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