I have a Carrier central A/C and a Propane FAG furnace in my basement. The problem is that after the A/C or furnace has shut off, the fans continue to cycle off and on just as if the A/C or furnace was still running. Sometimes the fans (there is 2 of them, I believe) run continuously and sometimes they shut off. The small fan which seems to be connected to a 6" vent runs first and then I hear a humming noise from time to time and then the blower kicks off and on. I have the "Heat/Cool switch in the OFF position and the Fan is in Auto. Both the Heat and the A/C work fine but, after the house is either cooled or heated, the air return sucks it all out and the selected function must turn on again to do its job...TOTAL waste of electricity AND Propane!! I've read the posts and the standard answer is the fan relay but, I don't believe this to be the problem because...eventually, the fans WILL stop running...usually late in the evening and stay off all night. But, when I turn it on in the morning....it all starts over again. Wife likes it...says there's always fresh air in the house.....yea but, at what COST?? There was an old Thermostat..Honeywell w/mercury switch that I replaced with a new Hunter 40035A but, that wasn't the problem cause it still cycles the fans. They will cycle for an hour or so and then shut off for a while and start back up again. I called Hunter Customer Service and he said it probably wasn't the thermostat...rather a problem in the fan circuitry?? Can anyone shed some light on my problem or should I just call the HVAC man hand him a blank check?? Any help would be greatly appreciated...Thanks

tkrussell

Get yourself a meter that can measure from 24 volts to 240 volts, and has an ohmeter, or even a continuity tester. Follow the wires from the fan back thru the entire circuit, thru the controls looking for the device, usually a relay, to determine what controls it.

The relay contacts may be pitted causing them to stick or the motion of the contacts may be restricted some how from moving. Or the relay is fine and it is because of a reason in the control circuit.

The relay will be wired thru control devices, such as high/low limit switches located on the heat box of the furnace, telling when the fan is to be on or off.

Check your manual , there usually is a "Sequence of Operation" list, explaning exactly which switch operates at which condition, from turn up the thermostat, until the unit cools down.

But if you do need to call in a technician, rest assured you are not giving him a "boat" payment. Techs usually make a decent pay, but the knowledge they have does not come easy.