I'm hoping someone here can help solve a problem that has mystified everyone else.
I have a Coleman Heat Pump (HC8B036F1) and modulating furnace (FC9C080C16DH11). It generally runs fine without any issues except for one intermittent problem.
Every few days, following a heating or cooling cycle, the blower will go to around 70% and stay there indefinitely. It continues to run even though the thermostat is no longer calling for heating or cooling.
I know the thermostat is not calling for the fan as I can turn it to the OFF position, and the blower keeps going. I've even pulled the thermostat face off the wall, which would prevent any signal from being sent, and the blower still runs. The only thing I can do to stop the fan is to manually set the thermostat up or down (until the "Heat On" or "Cool On" appears on the thermostat) and then cancel the temporary setting so that the "Heat On" or "Cool On" disappears. When I do this, the thermostat clicks on and off, and then the blower turns off after a few seconds.
When this intermittent problem occurs, if I do nothing, the blower will continue to run until the next heating/cooling cycle, at which time the blower will stop as it normally would after the thermostat clicks off. The only other way to stop the blower when it gets stuck like this is to cycle AC power to the furnace.
When this problem occurs, it is always after the heat pump outdoor unit has turned off and the furnace is not producing any heat. The settings on the furnace board are:
RECIRC = C
DELAY = A
COOL = A
ADJUST = A
AIR = NOM
There are no stored error messages.
I have had this intermittent problem since the day the furnace and heat pump were installed. I reported the problem to the dealer who later came and replaced the motherboard under warranty, but to no avail.
Not sure where to go from here. Any ideas or suggestions would be appreciated.