Air Conditioner Outside Unit Freezing Up – What Could Be Wrong?

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Many things can contribute to your HVAC system becoming faulty overtime. Items such as structural damage and worn out parts and components can plague your a/c unit and cause it to malfunction. However, an all-too-common issue with air conditioning units is the actual freezing up of the a/c unit itself.

An a/c “freeze-up” occurs when a layer of ice forms on the exterior of your air conditioner, causing it to make noise (other than it’s usual operational sound) and preventing it from blowing cold air.

Air conditioner covered with icicles on a yellow wall, Air Conditioner Outside Unit Freezing Up - What Could Be Wrong?

Reasons Why An Outdoor AC Unit Could Freeze

There could be several reasons for this, including the following:

  • Refrigerant Leakage
  • Drain Blockages
  • Outdoor Temperature Changes
  • Clogs Due to Dirty Filters
  • Thermostat Malfunctions

When ice buildup on your air conditioner prevents it from cooling effectively, it places a lot of stress on the unit’s compressor. Over time, this stress can lead to a weakened compressor (an expensive repair) and the wearing down of other internal components.

Having your a/c unit freeze up can be a headache to deal with, especially when spring arrives and temperatures begin to soar. Below, we’ll cover some of the reasons why an a/c unit may freeze and what to do when it happens.

A Closer Look At The Factors That Cause A/c Units to Freeze

Let’s look at the various factors that can cause your a/c unit to freeze up.

Refrigerant (aka “coolant”) Leakage

The coolant in your air conditioner is responsible for pressure and temperature changes. If there is a leak in its evaporator coils, it can cause the system to freeze over completely. These leaks can also come from the condenser coils due to holes in their U-bends and leaks in the coolant line sets, which may cause leaks due to broken joints. If you find that you’re continually adding new refrigerant to your a/c unit and it’s now frozen up, it could need coolant replenishment and leak repair.

Drain Blockages

In the absence of sufficient drainage, the condensed water from your HVAC system will remain trapped and can freeze over time due to the cooling process. The entire purpose of the drain is to take the water from the coils to the drain pan. When the coils freeze up, the drain can get clogged and cause serious freeze damage as ice gathers on the coils and shuts down the system.

Outdoor Temperature Changes

Air conditioners operate within specific temperature ranges and typically will not run efficiently under about 60 degrees Fahrenheit. During colder seasons, and depending on your location, nighttime temperatures may drop far too low for the a/c unit to function well. If the air outside is too cold, it will cause the pressure inside the air conditioning unit to drop and, as a result, freeze up. If your a/c unit freezes up, be sure to turn it off so that it may thaw out.

Clogs Due to Dirty Filters

Ice on the air filter of the air conditioner

Clogged up air filters is one of the biggest culprits of HVAC system malfunctioning. When debris and dust build up inside the filters, this places a massive strain on the system and prevents airflow. Anything restricting the airflow in your a/c unit can cause your evaporator coil to freeze up, as it won’t have enough heat to absorb. To fix this, you may need to have the unit cleaned or repaired, in addition to changing the air filters.

Thermostat Malfunctions

A freeze-up can also occur due to issues with the unit’s thermostat or sensors in the HVAC system overall. If the thermostat is malfunctioning, it can cause your AC unit to run continuously, despite current low temperatures. Continual running will cause the air conditioner’s condenser coils to freeze up, and as a result, the entire system can shut down. Faulty thermostats can be re-calibrated to perform correctly or replaced if they’re beyond repair.

Do not attempt to repair your frozen AC unit yourself; there are steps that you can take to prevent further damage and possibly pinpoint the cause of the freeze. Troubleshooting can help you save on diagnostic costs when contacting an HVAC specialist. Let’s go over them.

1. Turn the AC unit Off

When you notice a buildup of frost on the unit or a restriction of airflow from the vents surrounding your home, power off your air conditioner unit. If you find that the a/c unit is already frozen up, doing so will allow warm air to blow over the evaporator coil, allowing it to thaw out.

2. Inspect the filter

As mentioned previously, dirty filters will drastically reduce the amount of airflow across the coils. The reduction in airflow will cause the coolant temperature to drop much lower than necessary, resulting in a frost buildup very quickly. If your system freezes and a clogged up filter seems to be the cause, turn the system off, replace the filter, and give it at least 24 hours before restarting it again.

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3. Check the Evaporator Coil Drain Line

If the drain line is blocked, the moisture that your air conditioner removed from the air cannot escape, and as a result, it will freeze up. A blocked evaporator coil drain line will also cause water to accumulate in the drain pan–take note that this may result in water damage to your home.

5. Open and Clear All Vents

When the vents supplying air your home are closed off, air blowing over the indoor coil is reduced, and it will result in the same effect as a freeze-up caused by a dirty filter. Check that all of your vents are open and free of debris and dust buildup.

Quick note: It’s imperative that you not try and fix anything on your own as this can void your warranty. More importantly, it can be very dangerous due to the electrical components and toxic coolants in an a/c unit.

Should I Cover My Outdoor AC unit?

It’s not necessary to cover your outdoor air conditioner unit. While these covers can help to protect your a/c unit from debris and harsh weather, they can also trap humidity and cause mold to grow on the electrical components and internal wiring of your unit. They can also be a breeding ground for rodents and other small pests, as they provide insulation from extreme outdoor temperatures.

Nonetheless, many HVAC specialists recommend that if you do choose to cover your air conditioner unit that you purchase PVC-coated polyester mesh covers, which can prevent mold from growing inside the a/c unit and keep debris from blowing into the air conditioner.

It’s also helpful to perform the occasional spot check by walking around your air conditioning unit with a broom to brush away any visible debris clumps or layers of dust.

How Long Does It Take AC Coils To Unfreeze?

Frozen air conditioning unit

Thawing out your evaporator coils can take up to 24hrs. In many instances, you may be able to simply defrost your air conditioner on your own. If you believe that your evaporator coil is frozen, you should avoid running the a/c unit, as this can place great strain on the compressor and intern potentially cause it to burn out. To start the thawing process for the coils, locate your electrical breaker box and turn off the switch that controls the power to your AC unit.

It’s best not to attempt to remove the ice by hand because this could damage the components. Once the coils and the condenser have thawed out, be sure to remove any standing water that may have gathered around the unit.

Will An Air Conditioner Work Without Coolant (Freon)?

Your AC unit wouldn’t be able to cool your living space without any refrigerant. If you find that your air conditioner is blowing warm air or simply isn’t getting as cool as it had in the past, you may need to replenish your refrigerant level.

You should never attempt to continuously run your AC unit on low amounts of coolant as many of the air conditioner’s internal components require a certain level of refrigerant to perform optimally. When AC units are installed, the HVAC tech ensures that the correct level of refrigerant is measured and added to the unit. If the refrigerant level is inaccurate, it could be a result of your unit noting being properly configured when it was initially installed.

Air conditioner coolant can leak from your unit when there are loose connectors or certain parts worn out from usage. If the unit continues to leak refrigerant, it may not blow any cool air whatsoever. Even refrigerant levels that are just slightly lower can cause issues with important components inside the unit, such as the compressor.

An air conditioner’s compressor converts the coolant into a pressurized gas so that it is able to pump through the unit. Compressors are sized to operate with specific levels of coolant, which is based on the overall cooling capacity of the AC unit. When the amount of refrigerant drops too far for the compressor, it can not work as efficiently and will eventually require replacement.

The fact is, several components of your air conditioner may wear out faster than they normally would if the coolant is low or remains at undesired desired levels. When these parts of your AC unit are forced to overwork in order to keep your house cool, more energy will be required from the unit. This also means a potentially higher energy bill and more money spent on maintenance.

So to say, maintaining an optimal level of refrigerant in your air conditioning unit is absolutely crucial to its lifespan and performance.

In Conclusion

As you’ve learned, there are quite a few factors that could cause your A/C unit to freeze up and stop working. While it’s ok to try and troubleshoot the underlying cause of this yourself, it’s always recommended that you contact an experienced HVAC professional to get your unit back up and running quickly and safely.

This Post Has One Comment

  1. GasNtools

    Thanks for sharing an informative post . It really helped a lot..

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