How To Tell If AC Is Frozen? 3 Tell-Tale Signs (Ice On Evaporator Coils)

An air conditioner can freeze over. This happens quite often. If you suspect that your AC unit is not performing as it should, one of the first things to check is if the AC is frozen over. How to tell if AC is frozen?

Here is what happens when AC freezes up:

  • In most cases, the indoor evaporator coils are frozen. This is the case for mini split ACs, central air window ACs, even for portable air conditioners. You can detect if these AC coils are frozen yourself and unfreeze them (thaw a frozen AC unit).
  • In very limited cases, the refrigerant lines are frozen. This is quite an extreme case and it is very hard to tell if your refrigerant lines are frozen since they are hidden inside the walls. In this case, you can DIY the detection and unfreezing; calling a professional is a must in this limited case.
If you have a mini split AC, the frozen part are the evaporator coils (located in the indoor air handler).

Now, whenever an AC starts misbehaving, you don’t go ahead exposing evaporator coils to check if there is ice on them. There are specific tell-tale symptoms that a frozen air conditioner will have. The way you tell if your AC is frozen in checking these signs.

If you detect any of these signs you should stop the AC immediately and check the AC coils for ice (we’ll look into how to have a look at these evaporator coils later on).

Here is how to tell if your AC is frozen:

3 Tell-Tale Signs Of Frozen AC Coils

In more than 90% of cases, frozen AC means that evaporator coils are frozen. These are indoor coils, located in the indoor air handler (mini splits), inside part of the window AC, or in the pre-duct indoor part of the central air conditioner.

Basically, ice forms on the surface of these coils because they are either too cold for too long or because the airflow over cold coils is not sufficient.

How To Tell If AC Is Frozen ice on evaporator coils
Tell-tale signs of frozen AC unit are the direct result of this brownish ice formation on the AC coils.

Here is what you will see if your AC coils are frozen over:

  1. AC is blowing warm or even hot air. This is the #1 tell-tale sign that your AC is frozen. Namely, an indoor fan created an airflow over frozen indoor coils. The formation of ice on the coils prevents the coils from cooling the air. What you will see is an insignificant reduction in air temperature as it travels over the frozen coils and the result will be AC blowing room temperature air (usually warm air or even hot air).
  2. Decreasing the set temperature doesn’t decrease the temperature of the air coming from the AC unit. When you decrease the set temperature, the coils should get colder, and you should get colder air. If the coils are frozen, decreasing the coil temperature will freeze the coils even further, even more ice will gather on the coils, and there will be no change in the temperature of air from the indoor air handler, window AC unit, from the ducts, and so on.
    warm air from ac is how you tell ac is frozen over
    If AC is frozen, changing the set temperature on the thermostat will usually not impact how cool the air handler blows.
  3. Increasing airflow will have no effect on cooling. If the evaporator coils are frozen, pushing more and more air over them (switching the AC unit to ‘High’ setting) will have no effect on the temperature of the air coming from the AC. Usually, if we see AC blowing warm air, we switch it to the ‘High’ setting to get colder air. If the AC unit is frozen, even switching to the ‘High’ setting will have absolutely no effect on cooling.

As you can see, the main symptom of a frozen AC unit is warm air coming from the indoor air handlers. If the ice is already formed on the coils, decreasing the coil temperature or increasing the airflow over the coils will have no noticeable effect on cooling.

When that happens, you do have a problem. You can very well suspect that you have a frozen AC unit. To confirm if the culprit for warm air coming from the AC is truly a frozen AC unit, you should check if there is ice formation on the coils themselves.

Here is how to do that:

How To Check If AC Coils Are Frozen (Confirmation)

Visual confirmation is necessary if we suspect that our AC is frozen over. This literally means that we have to unscrew parts of the indoor air handler and have a look at the coils themselves.

Note: In any case, if you suspect AC is frozen, shut it down immediately to prevent further damage to the unit. Only after it is shut down, you can start digging through the unit to get to the evaporator coils.

Here is the step-by-step guide on how to inspect AC evaporator coils for ice accumulation:

  1. Shut off the power to the indoor air handler. You can do that via a switch or at the circuit breaker panel. Just be sure that there is no electricity in the air handler.
  2. Removing coil access panel. You will see screws holding the cover secured on the indoor air handler. Unscrew these screws and take the cover off.
    how to check if evaporator coils are frozen
    You can unscrew the cover and remove the access panel while the unit is still mounted on the wall, or take it off the wall and do it on the floor.
  3. Below the cover, you will find the access panel. Remove this panel very carefully to expose the evaporator coils.

You should be looking at the evaporator coils now. If you are looking at clean copper coils (slight orange or silver color), the coils are not frozen. However, if you are looking at brownish ice on the coils, the coils are truly frozen.

That brownish ice is frozen water mixed with dirt, dust particles, and so on; that’s why the ice of the coils is not transparent as normal ice. It has a brownish color.

This is the 101 how to tell if AC is frozen. If you have a window AC unit, you can check here what causes a window AC unit to freeze up. Hope this helps.

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