If your system is not providing any heat to the home, then you can begin your heat pump troubleshooting at the thermostat. Ensure that it is on heat and set above the room temperature. If you have a digital thermostat, then set the desired temperature to about 2-4 degrees above room temperature. This should make only the heat pump part come on and not the backup electric elements. (If you do not have a digital thermostat, we would highly recommend replacing your thermostat.) Now, turn the fan switch to on.
If the fan doesn't start, then check the fuses/breakers for the air handler or furnace. If the breaker was tripped, the problem could be a bad wiring connection, the blower motor, or the control board. If the breaker was not tripped, the problem could be the thermostat, low voltage wiring, or the fan relay.
If the fan is running, turn the thermostat to emergency heat. Ensure that the setpoint is at least 5 degrees above room temp. Wait for about a minute, then check to see if warm air is coming out the vents. If there is, then the problem is with the outdoor unit.
If there is not, the problem could be the thermostat or something in the air handler. You can use our electric furnace troubleshooting guide to diagnose and repair the problem.
If you have decided the problem is with the outdoor unit, return the thermostat to normal from emergency heat. Wait a couple of minutes, then continue your heat pump troubleshooting at the outdoor unit.
Is there a lot of ice/frost buildup on the unit? If there is, The problem is either a defrost control or the unit could be low on refrigerant. You can test the defrost control by manually forcing it to defrost. On older units, they had a defrost timer motor and you could manually advance the timer motor to initiate defrost. If you do so and the unit does not go into defrost, the timer motor is probably bad. On newer units, they have an electronic defrost control board. They typically have a set of pins that are jumped to manually initiate defrost. If you do so and the unit does not enter defrost mode, the board is probably bad.
Is the outdoor fan running? If it is not and you live in a colder area, the unit may have an outdoor thermostat installed. If it is colder than the setpoint the unit will not run. Otherwise, you should continue your heat pump troubleshooting by checking the high pressure cutout, for a wiring problem, the fan motor, or the run capacitor.
If the fan is running, feel the refrigerant lines. The bigger line should be warm. If it is not, the problem could be a wire in the unit, the compressor run capacitor, compressor, or the unit could be low on refrigerant.
**NOTE** It is best to check the charge of a heat pump with the unit running in the cooling mode. If possible, wait until the outdoor temperature is above 55 degrees.
The final step in your heat pump troubleshooting should be to run the unit through a normal heating cycle. It is a good idea to check the temperature rise of the system after it has been running for 10 -15 minutes. You can do so by measuring the temperature of the air coming out of the vents and the temperature of the air entering the fan coil. Subtract the entering air temperature from the leaving air temperature to find the temperature rise. This should typically be 15 to 20 degrees.