Defrost Cycle

Written by All American. Posted in Information

When it gets below about 45 degrees, a heat pump running in HEAT mode may develop ice or frost on the coils. There are exceptions to the rule, however, as I have seen heat pumps defrost when it is above 45 degrees and even in the 50’s! If it gets frozen enough, it may have to defrost.

A defrost cycle is initiated by the reversing valve switching the flow of Freon and putting the unit in COOL mode. However, unlike when the unite is running in COOL mode on a hot day, the fan blades in the outdoor unit are not spinning, and the system typically has its electric, gas, or oil backup heat running to prevent the heat pump from effectively air conditioning the house while it is defrosting. Sometimes, depending on a number of factors, a steam or fog may appear above the heat pump.

A defrost cycle can last anywhere from less than a minute to ten minutes or more depending on a number of factors, including outdoor temperature, ice/frost buildup on the outdoor coils, whether or not it is raining or snowing, and what temperature the thermostat is set at.