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Re: Fan Runs all the time
The fans run for an additional minute or two after the set is turned off.
If the fan runs longer than that, then, either the 12 volt relay is stuck or the transistor that controls that relay is shorted.
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without knowing age of unit, I suggest replacing the motor. Sounds like the armature is worn the bearings and is moving inside the windings of the motor. I would do that first before moving forward with any other repairs.
your thermostat could be wired in to a energy recovery venilator which will bring the unit on for a certain amount of time every hour some thermostats have recirculate mode which will do the same thing to help filter the air
Most T-Stats have a On / Auto on a forced air system. On means the fan will run all the time even if it is not calling for heat. Auto only runs when calling for heat. Does the fan turn off in the auto mode at all? To test it...BE SURE THE FAN IS IN THE AUTO MODE ON THE T-STAT... Turn the thermostat all the way down and keep it there for appox 15 mins. If it is wired properly and the fan limit is set properly the fan should turn off. If it doesn't it is not the thermostat were the problem lies.
Most forced air units have a fan / high limit switch. There is a setting on the switch for the fan to turn on and a setting for the fan to turn off or it has a setting and a differental switch for it to turn off/on. Example - the fan comes on when the temp in the heat exchanger reaches 110 degrees F and will shut down at 95 degrees F after the thermostat is satified...this would hav a differental of 15 degrees F. It may be set to low and the fan continues to run long after all of the heat has been removed from the heat exchanger. This in turn will cause cool air to be coming out of the registers.
When was the last time you had the coils in the condenser cleaned. Dirty coils can insulate the refrigerant tubes, causing the fan to constantly run in order to try and cool down the refrigerant returning from the evaporator coils(a-coils) in supply ducting, But can.t because the condenser coils are insulated not allowing the heat to escape. I would try this first before replacing expensive parts. It is the small things that we overlook that is most likely the source
this set has more then one fan; one fan will run all the time to cool the digital circuit board---if it is the actual LAMP fan then you have a problem---the digital fan is very small and not located near the lamp.