Mini-Split Musings

How Does a Mini-Split Defrost Cycle Work?

March 11, 2019

A mini-split or ductless system can cool the air in the summer and heat a home in the winter. One of the more clever things about this technology is that it uses the same chemical reaction to achieve both processes but applies it in different ways.

In the winter, a ductless system occasionally turns into an air conditioner to keep operating in a way that will warm your home. But how does this happen and why? It’s all about the chemistry of changing states and how ductless systems use it! Keep reading to learn more about the mini-split defrost cycle.

The Cooling Process


First, let’s look at how a ductless system cools your home in the summer. A mini-split ductless unit relies on chemical reactions, and in this case, the way liquid can boil and eventually turn into gas or vapor, and how that vapor can cool down and return to a liquid state.

Changing a state from liquid to gas and back again takes energy, and that energy is expressed in different ways. A ductless system operates bringing vaporous refrigerant into the mini-split unit. When it comes in contact with warm air, it absorbs that heat, cooling down the air, and turning back into a liquid. That liquid form of the refrigerant is then sent back to the compressor outside, where it gets rid of the warm air, radiating it away from your home, and being converted back into gas form to get cycled back to your house.

The Heating Process & Defrost Cycle


When a mini-split system heats a home, it essentially reverses the process above: cooling itself outside in the compressor so that the warmed refrigerant can travel to the mini-split unit and release its heat in your home.

Now that the air outside is getting cooler, frost and ice can form on the compressor. If that buildup were left untouched, it can eventually impair the unit’s performance. So occasionally, to get rid of this ice or frost buildup, a mini-split ductless unit will shut down the fan. That avoids blowing cool air into a home that’s being warmed. The unit goes into air conditioning mode, radiating heat back outside, to clear out ice and frost build up. The defrost cycle ensures that your mini-split unit continues to operate efficiently and heat your home.

The Frequency of the Defrost Cycle


In colder weather, the defrost cycle may kick in more frequently. It isn’t usually an excessive problem here in Washington State, where the winters aren’t too severe. So, if you see ice buildup on your compressor, leave it alone. Don’t try to pick it off yourself, as your ductless system has a measure in place to take care of it.

However, if you see that the ice isn’t going away, that might indicate a more technical problem. You should call an expert to see if you need repairs or a replacement.

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