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My outside heat pump comes on but the indoor blower fan does not come on unless I raise the temperature on the thermostat, then the inside fan motor comes on. When I lower the thermostat below room temperature, then both the inside and outside units go off. If I don’t touch the thermostat at all, the heat pump will run forever and the inside blower motor will not come on. Do you know why this is happening?

GIL, ACCOKEEK, MD

Heating units can opperate differenly depending on the manufacturer. But in most instances the blower is either controlled by the thermostat or the indoor unit itself. You stated that the blower will turn on when you raise the thermostat, which makes me believe that by raising the thermostat setting you are actually causing the auxiliary (emergency) heat to come on with the heat pump. This is normal anytime you raise the thermostat setting more than a couple degrees. Your blower may operate differently depending on if the heat pump is heating the home or if the auxiliary heat is. If raising your thermostat turns on the heat pump then typically it means the indoor fan is controlled by the thermostat. But if the home is being heated by the auxiliary heat then it is actually the circuit board or relay inside the furnace that will turn on the indoor fan. So by raising the thermostat setting you are turning on the auxiliary heat and since the auxiliary is activated it turns on the indoor fan.

The problem could be a faulty thermostat, a broken wire from the thermostat to the indoor unit, a bad circuit board/relay. But if you have replaced the thermostat recently or purchased one at a local home improvement store, make sure the thermostat is set up correctly. A lot of these thermostats are designed to work with either a gas furnace or heat pump and must be set properly for them to operate correctly. If this does not correct the problem I would recommend you have qualified technician check the unit. Running the heat pump without an indoor fan for an excessive amount of time can damage the heat pump compressor so I would not operate the heat pump until the problem is fixed.