A heat pump has two basic modes of operation and the steps to diagnose a problem are a little different. When troubleshooting in the cooling mode, the process is essentially the same as diagnosing and repairing an air ducted central air conditioner.
Cases where the unit does not provide heat
If your system does not provide heat to the house, you must start the diagnosis with the thermostat. Make sure that it is in heat mode and set to a temperature above room temperature of about 2 to 4 ° C (If you do not have a digital thermostat, we strongly recommend replacing it). Now start the fan switch.
If the fan does not start, check the condition and location of the fuses or circuit breakers. In general, these are triggered in the event of poor wiring connection, the fan motor, or the control board. If the circuit breaker has not been tripped, the problem could be the thermostat, low voltage wiring, or the fan relay.
If the fan is on, turn the thermostat to heat. Make sure the set point is at least 5 degrees above room temperature. Wait about a minute, then check to see if hot air is coming out of the vents. If so, then the problem is with the outdoor unit.
If there is no hot air, the problem could be the thermostat or something in the air handling. Outdoor unit troubleshooting
If you find that the problem is with the outdoor unit, return the thermostat to normal, wait a few minutes before resuming the diagnosis.
Is there an ice deposit or frost on the device? If so, you can test the defrost control by manually forcing to thaw. Older units have a defrost timer motor and you could manually advance the timer motor to initiate defrost. If you do and the unit does not defrost, the timer motor is probably faulty.
On newer units there is an electronic defrost control card. This is usually a set of pins that are installed to manually initiate defrost. If you activate them and the defrost mode no longer starts, the electronic board is probably defective.
Is the outdoor fan on?
If it is not and you live in a cold area, you may consider installing an outdoor thermostat because if it is colder than the value displayed by the setpoint, the unit may not start. If not, you must continue your diagnosis by cutting off the high pressure, for a possible wiring problem, the fan motor, or the running capacitor.
If the fan is on, check the refrigerant lines. The larger line should be warm. Otherwise, the problem could be a wire in the unit, the running capacitor, the compressor or the unit could be slow on refrigeration.
Final checks
The last step in your diagnosis 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 10 to 15 minutes of operation. You can do this by measuring the temperature of the air leaving the vents and the temperature of the air entering the fan coil. Subtract the incoming air temperature from the outgoing air temperature to get an idea of the temperature rise. This should typically be 15-20 ° C