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Hometown Heating and Air Conditioning Blog

Why Is Ice Forming on My AC’s Evaporator Coil?


A common question that we get from homeowners during the summer is: Why is ice forming on my AC’s evaporator coil? Although you might think that the appearance of ice on an air conditioner is normal–after all, it’s a system designed to make things cold–it’s an indication that something is wrong with your AC. 

Ice should never appear on any part of your AC system. Not only does the ice itself create a problem, but the reason why the ice is forming may be an even worse issue. Let’s go over why your AC ices over in the first place and what it can possibly mean. That way, if you see this happening with your air conditioning in Walnut Creek, you’ll know what to expect. 

Why Is Ice Forming on My AC?

In a nutshell, the main reason behind it is when the evaporator coil loses its ability to absorb heat and raise the temperature of the refrigerant moving through it.

When the refrigerant in the coil doesn’t warm up past freezing, which is what normally happens in a cooling cycle, its low temperature will cause moisture along the coil to freeze. Moisture naturally forms along the coil when the AC is operating, so there’s always some amount of water to freeze if the coil is too cold.

This leads to a snowball effect (no pun intended) as the ice further exacerbates the coil’s ability to absorb heat, which leads to the formation of even more ice. If ice coats the entire coil, the AC won’t be able to provide any cooling at all. Some homeowners will notice that their AC isn’t working at all before they noticed the coils are frozen over.

The Source of the Problem

So why does the coil lose its ability to absorb heat? Here are some causes:

  • Low refrigerant charge: A leaky air conditioner can result in a drop in the air conditioner’s refrigerant charge. When there’s a lower amount of refrigerant, that reduces heat absorption. A leaking AC is the most common cause of an iced-up evaporator coil.
  • Dirty evaporator coil: If dust and dirt make their way into your AC system, usually because of a dirty air filter, the dirt can settle onto the evaporator coil. This creates an insulating layer that lowers the heat absorption.
  • Clogged air filter: When the air filter for the AC becomes clogged, the blower won’t be able to move enough warm air across the coil for it to absorb.
  • Malfunctioning blower: If the blower fan isn’t pushing the right volume of warm air over the coil because of a malfunction, it can cause this issue.

The first and only thing you can do to try and fix this issue yourself is to check the AC filter. If it’s dirty, replace it. Allow the coils to thaw (never attempt to manually scrape the ice off!) and then turn the AC on. If it’s still icing over, it’s usually one of the other causes and it’s time to call us for a repair.

Please don’t hesitate to reach out to the team at Hometown Heating and Air Conditioning to discuss your AC’s performance! Your comfort is our business.

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