Fan shut off when heat pump comes on troubleshooting
We're having a problem with the fan turning off when the heat pump comes on. I've replaced the motor, compacitor, and thermostat. But still the same problem. The fan works fine in emergency heat mode but when the Lennox heat pump comes on the furnace fan starts buzzing then turns off. Any suggestions as to what the problem may be that I can take a look at?
How old is the air handling unit (furnace) you are working with? Sounds like it may be an older model that has a fan relay to start the fan in heat pump mode that isn't closing.
Is it by chance an electric furnace? Most have 2 relays to bring on the fan motor, one is 240 volt and turns on the fan when there is a call for emergency heat (through the sequencer), the other is operated off of 24 volts and gets it's signal from the thermostat (G terminal). Anybody tried changing the thermostat lately?