Home » The Defrost Cycle: Our customers ask… and we deliver.

The Defrost Cycle: Our customers ask… and we deliver.

“My air conditioner is covered in frost, making loud noises, and the fan stopped. Please come fix it.” – a valued One Hour customer

It’s actually your heat pump that’s covered in frost.  Heat pumps cool our home in the summer and heat your home in the winter and run a defrost cycle as needed.  It’s that time of year again: cold outdoor temperatures, heat pump condensers covered in frost and loud noises coming from these units.  Every winter our customers question these conditions, and we don’t blame them for asking.  Most people are not familiar with the 3 cycles of a heat pump: heating, cooling & the defrost cycle.

Why is there frost on my heat pump?defrost cycle, HVAC, frost on air conditioner
Frost is fairly normal in the winter under certain conditions.  When the heat pump is heating a home and the outdoor air is cold, the outdoor coil acts as an evaporator.  The outdoor coil has moisture on it that’s evaporating, and under certain conditions of temperature and relative humidity, frost might form on it’s surface.  A frosted coil is inefficient, so heat pumps have a built in solution for this normal frost situation: the defrost cycle.

Why is the heat pump making loud noises?
This is the defrost cycle kicking on to eliminate or prevent frost on the condenser coils.  The loud noise is the sound of the valve reversing  directions of refrigerant in the system.  Temporarily the system will heat the outdoor coils to 57 degrees F and melt or prevent any accumulation of frost.  This is intentional and happens during cold weather, when outside temperatures approach or go below freezing.  The colder the outside temperature, the louder these defrost cycle noises.  A typical defrost cycle might run from 30 seconds to several minutes, and might occur regularly at timed intervals or as needed.

Why did the fan stop moving? It must be broken.
This is also a normal feature of the defrost cycle.  During defrost, the movement of air across the coils is not needed because it would slow down the heating of the coils that are dealing with the frost.  A moving fan would be less efficient, so it’s turned off during the defrost cycle.  With the fan off and decreased air flow, the coils will heat to 57 degrees F faster.  No fan?  No problem during defrost cycle.

Is that steam coming from my unit?
As frost melts, you may see some water vapor rise.  After defrost, when the heat pump resumes normal operation, leftover moisture and sometimes water vapor caused from the warming coils and melting frost remains.  The fan starts spinning and this “steam” will exit the system upward, with the fan’s airflow direction.  This is normal as well.

What do I do?
Don’t panic.  Give the system time to properly complete the defrost cycle.  After defrost is completed, it will return to normal operation. The defrost cycle can kick-in regularly throughout a cold day or night.

If your heating & air conditioning system is failing to heat or cool your home properly, please call us at 843-448-6867 or fill out the form on the contact page and we’ll be in touch shortly.


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