Heat pump defrost cycle

[Beelady]

My Carrier-brand heat pump is 5 years old. Since it was first installed, it goes into a defrost cycle as often as every other time it runs when the outdoor temperature is well above freezing (upper 30's to low 60's). This defrost cycle is shorter than the one when the heat pump legitimately needs to defrost; I can hear the difference in the two. The company that installed it and has maintained it doesn't know what to do; they finally replaced the "defrost panel" last summer, but that made no difference.

Any ideas? I worry the problem defrost cycle will shorten the life of the unit. My electric bill seems fine, so it does not appear to be using excessive electricity.

[LazyPup]

Your unit is functioning exactly as it should.

A heat pump is in essence an air conditioner running in reverse. When in the heat cycle the outdoor coil is operating as the evaporator and the inside coil is operating as the condenser.

As the liquid refrigerant enters the outdoor coil it is boiled to a gas by absorbing heat from the atmosphere. The actual amount of heat being absorbed is determined by the efficiency of the unit. Years ago the temperature differential was 12degF but they are now making units that operate at 14, 16 or even 18 degF differentials. This means that the actual temperature of the evaporator coil is dropping by 12 to 18degF. Understanding that icing will occur when moisture drops to 32degF it then stands that in a heat pump outside coil the moisture in the air can ice when the outdoor temperatures are as high as 32degF + the differential for you unit. This means that if you have a high efficiency unit icing may occur when the outdoor air temps are as high as 50degF or more depending upon the operating differential for your unit. Generally the units are set up to defrost slightly above the bottom theoretical temperature to insure their will be no problems.

The defrost operation is necessary and will not cause any undo harm to your unit.