The Meaning of De-ice Mode on Your Air Conditioner
When an air conditioner is in heating mode, its heat pump is extracting heat from the outside and transferring that air into your home to keep it warm. When the outside ambient temperature goes to 0 or lower degrees, the moisture from the air freezes on the heat exchange on the air conditioner while the unit’s fan continues to blow air across it. The deice or defrost mode is that mode the system enters into when it automatically detects that ice has started to form on the unit. It then starts fixing it.
You never want to stop the unit from doing this until the defrost cycle has ended. If it is stopped and the unit is restarted right away it could cause damage to the unit if not cause it to operate inefficiently.
Why must my AC perform a defrosting?
When ice builds up on the external heat exchange, the air flow is reduced. This causes the unit to experience an inefficient performance which can sometimes be drastic. In extreme cases, stopping the cycle can damage the outdoor unit.
How do I know my unit is in defrost mode?
You will notice that the unit stops heating indoors and outdoors, the fan will have stopped while the compressor continues to run. You will also notice a puddle of water around or under the unit outside.
Things to Expect
Your system may begin to make a whooshing-type of sound just as the fan stops inside. That is your clue that the system is cycling off and entering into de-ice or defrost mode.
You might also see what you could mistake for being smoke come from the unit outside. This is just steam and it is a common occurrence when the unit is in defrost mode on a cold day. The outdoor unit might also look white. This is just frost and will disappear when the unit resumes normal operation.