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What Causes Ice to Form on an AC’s Evaporator Coil?


A mistake that homeowners often make about the way their air conditioning systems work is to assume that ice appearing along the indoor evaporator coil is normal, just a sign the AC is working extremely well at cooling down the air.

The truth is that ice should never appear on any part of an air conditioner. When ice appears along the evaporator coil, it means something is interfering with the standard way the air conditioner operates. The ice creates a major problem on its own, but the source of the ice forming may be an even worse problem.

The Basic Cause of Ice Forming

There are several underlying causes of ice appearing on an AC’s evaporator coil which we’ll get to, but all create the same issue: for some reason, the evaporator coil loses its ability to absorb heat and raise the temperature of the cold 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 now begins a snowball-down-the-mountain effect. The ice further restricts the coil from absorbing heat, causing more ice to grow. If ice coats the entire coil, the AC won’t be able to provide any cooling at all.

The Sources of the Problem

Now that you understand the basic cause of ice forming, we can look at the reasons the coil may lose heat absorption:

  • Low refrigerant charge: An air conditioner can lose refrigerant to leaks, dropping the air conditioner’s charge (its set amount of refrigerant). Although it sounds strange that less refrigerant would cause ice to form, the problem this creates is that the lower amount of refrigerant reduces heat absorption. The remaining refrigerant in the coil will stay cold, and that’s more than enough to cause freezing to start.
  • Dirty evaporator coil: If dust and dirt start to get into the AC, it can settle onto the evaporator coil. This creates an insulating layer that lowers heat absorption and leads to the coil freezing over.
  • 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: Likewise, if the blower fan isn’t pushing the right volume of warm air over the coil because of a malfunction, it can lead to coil freeze.

Please do not attempt to scrape the ice off on your own, as this may easily damage and puncture the coil. It’s best to shut the AC off and let the ice melt (although this might lead to the condensate pan overflowing). To solve the underlying problem, call our professionals for air conditioning service in Madera, CA.

Call Purl’s Sheet Metal & Air Conditioning for the AC repair you need in the Central Valley. “Quality Is the Cornerstone of Our Success” since 1952.

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