AboutJ Cook Expertise With 25+ years experience, I am familiar with residential, commercial, and industrial HVAC equipment including but not limited to boilers, chillers, reciprocating and screw compressors. I am trained in all manners of control wiring.
Experience I currently have three HVAC licenses and Refrigeration license by the State of North Carolina. I have been in this field for over twenty years. I have been a service technician for a contractor and also worked at a state college in the repair and maintenance of steam lines and equipment. I am currently the Building Maintenance Superintendent for a municipality.
Question I live in Southern California and have a Carrier furnace model #28RC024000, serial #Y769329. The thermostat is a Honeywell RTH7000. Everything worked fine for the last year or so, but now the fan stays on all the time (won't shut off), but the heat and A/C don't come on. No matter what I do at the thermostat, it's just the fan running. There doesn't seem to be any communication between the thermostat and the furnace. I changed the batteries in the thermostat and ran new wire between the thermostat and the furnace, but still nothing. Any suggestions?
Answer The fan in heat mode is actually not controlled by the thermostat, it is either controlled by a temperature sensitive device, or a timer on the internal circuit board. It appears you may have multiple problems, but the main problem appears to be loss of low voltage. Open the indoor units panel and locate the transformer. Verify you have 240 volts feeding it and you have 24 volts coming out. It appears you will not have one or the other. If you do not have 240 volts, look for a blown fuse or a defective feeder breaker. If you do have 240 but not 24 coming out, you need a new transformer. After getting the 24 volts, your fan may clear itself as it is most likely on a fail safe circuit that energizes the fan on a loss of 24 volts so the heat exchanger will not be damaged. Thanks J
