What is usually the cause of an air conditioner evaporator icing up?

Author: Lilian Streich  |  Last update: Monday, March 31, 2025

The most common reason for frozen evaporator coils is insufficient airflow. This is commonly caused by a clogged or dirty air filter, backed-up drain clogs, low fan speed, or a dirty evaporator coil. Check to see how many registers are closed in your home.

What are the six common causes of evaporator freezing?

Causes of A Frozen Evaporator Coil
  • Reason #1: Dirty Evaporator Coils and Air Filter. ...
  • Reason #2: Refrigerant Leaks. ...
  • Reason #3: High Humidity Levels. ...
  • Reason #4: Malfunctioning Fan Blower. ...
  • Reason #5: Clogged Condensation Line. ...
  • Reason #6: Cold Temperatures. ...
  • Tip #1: Clean Your Air Conditioner. ...
  • Tip #2: Use a Dehumidifier.

How do I stop my air conditioner from icing up?

Clean or Replace Your Air Filter

If your AC system's evaporator coil isn't getting enough airflow through the air duct, ice will eventually begin to form along the coil. Luckily, this can be prevented, as you should be inspecting and changing or cleaning your air filter routinely regardless.

Will low refrigerant cause an evaporator to ice up?

While icing due to low refrigerant is rare, and often requires other problems, it can happen. Because the pressure in the evaporator is so low, the boiling point of the refrigerant is well below 32°F. This causes the coils closest to the metering device to be very cold, which causes moisture to freeze.

Is it worth it to replace an AC evaporator coil?

Adding more refrigerant is a temporary fix, but you'll continue to see poor air conditioning efficiency until you fix the underlying problem. In most cases, it's more cost-effective to get a new coil than repair an old one.

8 Reasons Why Your AC is Freezing Up

How do I keep my evaporator coil from freezing?

#1: Dirty air filter

A dirty filter can lead to a dirty evaporator coil and potentially a frozen evaporator coil. Prevent a clogged filter by changing your air filters regularly. This should be every 30-90 days depending on the quality of the filter, how hard your system is running, if you have pets, and other factors.

What does ice on the evaporator mean?

But when you go outside to see if your system is running, you see ice on your lines and coil. How is that possible? If this happens to you, then your evaporator coil is most likely frozen, which means that all that freezing cold refrigerant is flowing into the outdoor lines (causing them to also be covered in ice).

How to check if AC has enough freon?

Steps for Checking Refrigerant Levels
  1. Turn Off the AC and Remove the Cover. Turn off the AC unit and remove the cover to access the refrigerant level gauge or gauges.
  2. Locate and Remove the Access Panel. ...
  3. Attach Refrigerant Pressure Gauges. ...
  4. Interpret Pressure Levels. ...
  5. Add Refrigerant (if Necessary)

Can a dirty condenser cause a coil to freeze?

If mold and grime fill the drain, it also causes water to flow backward into your evaporator compartment. Since the evaporator coil is the coolest during a cycle, nearby water will freeze, almost instantly forming ice crystals.

Should I turn my AC off if it's frozen?

1st Step: Turn Your HVAC Unit Off.

Even if it's sweltering outside, you still need to turn OFF your air conditioner! Running a frozen air conditioner will wear out parts much faster, and could overheat your unit. Worn parts are bad news for the most expensive piece of your HVAC unit—the compressor.

How do I know if my evaporator coil needs cleaning?

Here Are Five Telltale Signs That Your AC Coils Are Dirty And Need to be Cleaned
  1. Your electricity bill has been going up. ...
  2. Your unit seems to be running longer for no reason. ...
  3. Your home doesn't feel as cool as it should be. ...
  4. The Coil is Covered in Frost While Running. ...
  5. Higher Indoor Humidity.

How often should I change my AC filter?

How Often Do I Need to Change Out My Air Filter? Generally, most air filter manufacturers and HVAC companies recommend changing your air filter every 90 days, or 3 months. That can change based on where your home is located (ex. dusty, dry climates), if you have any pets, and the age of your system and equipment.

How to stop ice forming in AC?

How to prevent ice formation in your AC
  1. Regular maintenance.
  2. Change the air filters.
  3. Unblock the air vents.
  4. Check the thermostat settings.
  5. Inspect the fan.
  6. Maintain adequate insulation.

Which of the following will cause an evaporator coil to freeze up?

Dirty coil

Over time, your system's evaporator coil will become covered in dust, dirt, grime, and more. This prevents it from getting the airflow it needs to properly move heat, which means that the system could then freeze over.

How to fix an air conditioner that freezes up?

Turn the Thermostat Fan Setting to On. Turn your thermostat fan setting to “On” so that the fan continues to blow air over the coil. The warm air in the home will naturally defrost the frozen coil. In severe cases, the heat can be turned on to speed up the process.

Can AC lose Freon without a leak?

While the refrigerant in your vehicle can escape even without a leak, it's often not enough to cause significant issues unless you've failed to top up the refrigerant for years. When the lack of refrigerant becomes significant though, it can cause a number of problems, including an overheating driver in the summer sun.

How often should I add refrigerant to my AC?

Most ACs nowadays come shipped from the manufacturer with the exact amount of refrigerant that it will need for the duration of its life. So, unlike a car, your AC won't ever need to “fill up” on refrigerant unless something goes wrong with the system.

Will AutoZone recharge my AC?

An AC leak will lead to warmer air from your vents over time. In most cases this can be fixed with a proven stop leak additive to seal up any leaks. When it's time for an AC recharge, turn to AutoZone.

Why does my evaporator keep frosting up?

The most common reason for this is that the air conditioner is getting insufficient airflow, which is commonly caused by clogged air filters, backed-up drain clogs, or a low fan speed. When there's a lack of airflow, there won't be enough heat to prevent the condensation on the evaporator coil from turning into ice.

How do you unclog an evaporator?

Use a can of compressed air (which you can purchase at any hardware store) to gently blow large particles of debris and dirt out of the evaporator coils. Any debris that is stuck can be worked away using your soft bristle brush. Make sure you are not using a metal or wire brush because it can damage the coils.

How to check refrigerant level in AC?

Steps to Check Refrigerant Levels
  1. Turn off the air conditioner and locate the service valves.
  2. Attach the manifold gauge set to the service valves.
  3. Turn on the air conditioner and observe the pressure readings, which should be between 30-40 PSI for most systems (though some may require higher or lower pressures).

How do I know if my AC evaporator coil is frozen?

Signs You Have a Frozen Evaporator Coil
  1. AC runs but never cools your home.
  2. Warm air blowing instead of cold.
  3. Ice buildup around the coil.
  4. The thermostat temperature doesn't match the indoor temperature.
  5. Frozen lines and ice buildup near outdoor units.
  6. Flooding near drain pan.

How to clean an evaporator coil without removing it?

Brush Off Loose Debris: Using a soft brush or a specialized furnace coil brush, gently brush away any loose dirt or debris from the coils. Be gentle to avoid bending the fins or damaging the coils. Vacuum the Coils: Attach a soft brush to your vacuum cleaner and carefully vacuum the coils.

Why does low refrigerant cause icing?

Low refrigerant can also lead to frozen evaporator coils. Without refrigerant passing through the coils, there will be no way for that absorbed heat to be transferred out of the air handler. The lack of pressure within the coil continues to drop, the moisture freezes onto the coils, and ice forms as a result.

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