Compressor failure
A compressor is the part of a heat pump that creates heat, and to reduce the risk of compressor failure, both the heat and cold carriers need to be at the right temperature.
When a heat pump cannot get rid of heat properly, it causes the oil in the compressor to crack. When the oil cracks, it cannot lubricate the bearings in the compressor.
Soot particles can also form in the oil, which can lead to the formation of acids in the oil. If acids are formed, they will corrode the electrical windings of the compressor's electric motor.
Therefore, you should always take an acid test before replacing a compressor. If there are acids in the oil, you should run a burnout filter x number of times to remove the acids in the oil!