When a heat pump frequently switches on and off, it is short cycling, and it can be caused by a number of different issues. An oversized system can cause short cycling, as can low refrigerant levels, a thermostat that doesn't work right, and, of course, a dirty air filter. Whatever the cause, this problem can lead to increased energy consumption, reduced comfort, and potential damage to key components of the system. In particular, short cycling puts a lot of strain on the compressor, and it can significantly reduce the life and the efficiency of the heat pump. A professional technician can diagnose and repair the problem.