Window Air Conditioner Freezing Up – What Could Be Wrong?

A malfunctioning window air conditioner can cause a lot of discomfort in your home. One common issue from these air conditioners is the "freezing up" of the unit itself, which can be caused by several factors. We've done a bit of research to help you determine the reasons why your window air conditioner may have frozen up and what to do about it.

There are quite a few reasons why a window air conditioner may freeze up. Here are the most common reasons:

  • Filters Need To Be Replaced
  • Dirty Evaporator Coils 
  • Air Conditioner Is The Wrong Size
  • Running Unit In Cold Temperatures

Throughout this post, we will discuss each of these reasons and provide important steps that you can take to prevent your air conditioner from freezing up. Please continue reading, and we'll also let you know how to best maintain your A/C unit.

Air conditioning sticking out the window of an Apartment in an Alley in New York, Window Air Conditioner Freezing Up - What Could Be Wrong?

Reasons Why Your Window A/C Unit May Freeze Up

If there is a build-up of ice on your air conditioner unit, it could lead to costly repairs, as this affects its ability to cool your home effectively. Let's look at each of the previously mentioned potential causes in detail.

Filters Need To Be Replaced

Whenever the airflow in an air conditioner is restricted, it will cause the unit's evaporator coil to freeze. There are several reasons why the airflow may be inefficient. One of the most common reasons is that the air filter is dirty and clogged. If your air conditioner is continuously running in your home, HVAC specialists suggest cleaning or replacing the filter at least once a month.

Checking the air filter routinely can help you prevent any possible issues caused by blockages. Additional airflow blockages can include closed or blocked duct, dirty evaporator coils, and a faulty fan.

Dirty Evaporator Coils

Evaporator coils can also become clogged up as a result of the unit having dirty air filters. If this is the case, you can clean them by using a warm damp cloth. Another option is simply contacting an HVAC technician to take the unit down and clean the evaporator for you. That being said, performing regular maintenance of the air filters and evaporator coil can go a long way in keeping your air conditioner performing in the best condition.

Air Conditioner Is The Wrong Size

Another common reason associated with window A/C units freezing up is that they are not sized correctly for the room they're in. Many times the unit is simply either too big or too small for the space that it's required to cool.

A window air conditioner unit that is too small will have to work double-time to effectively cool down a larger room. This increased workload can cause more condensation to form on the coils, leading to ice development.

If an A/C unit is too large for the space required to cool, ice can also form on the vents because it simply isn't running enough. Condensation will develop on the coils and condenser due to the unit being exposed to the sun (and warm outside temperature), and will eventually freeze up.

Running The Unit In Cold Temperatures

HVAC specialists recommend not running an outdoor A/C unit during cold weather for any reason. Why? Because of the lubricant inside the compressor that is responsible for its operation. The lubricant functions similarly to the oil in a car's engine, and just like the oil made for car engines, compressor oil for air conditioners comes in different grades.

The type of oil used in a window unit's compressor is summer-weight oil, a heavier oil that works best in warmer weather. It can heat it up and still give the compressor the protection and lubrication that it requires. However, the oil is much too thick to provide adequate coverage and lubrication for the compressor in cold weather, which will affect its ability to function.

Is It Bad To Cover A Window Air Conditioner?

While it might not be bad to cover a window air conditioner, it remains up for debate whether covering the unit is recommended. An air conditioner unit can be one of the most expensive appliances in your home or apartment. So, understandably, you'd want to protect this investment. HVAC specialists seem to be split on whether covering a window air conditioner is a good decision.

The reason is that the answer isn't black and white; rather, it depends on a few factors. Below we'll discuss some of the benefits of covering your window unit, as well as why some experts advise not to cover it. We'll also provide important factors to consider before opting to buy a cover.

Benefits of covering your window air conditioner in the winter include:

  • Protecting the cabinet; harsh winds that can blow through the unit into the home and debris can fall inside the vents.
  • Preventing air leaks can help you save money and conserve energy on your heating bills during the winter.
  • Keeping snow and other types of precipitation from blowing into the outer portion of the unit.
  • Detering birds and other animals from nesting.
  • Reducing snow and ice accumulation on the unit, thus providing an extra layer of insulation and protection.

Why Some Experts Say "No" To covering air conditioner units

The primary reason to not cover a window A/C is due to moisture accumulation. Many HVAC specialists argue that covers can cause the accumulation of moisture on the unit's condenser coils, which can cause rust to form. It can also cause the coils to freeze, which can result in an expensive repair or complete replacement of the unit.

Factors To Consider Before Buying A Window A/C Cover

Residence Type

Whether you live in a home and have the capability to cover the outer portion of your home in the winter, as opposed to living in an apartment building where this may not be possible. If you're renting, it's best to simply ask your landlord on whether or not it's okay to cover your window unit. After all, the landlord owns the appliance.

Geographic Location

If you live in a place with relatively mild winters (such as Florida), it may not be necessary to cover your window unit in the winter. However, if your location endures particularly harsh winters, it may be a good idea to cover it up.

Unit Brand/Model

Some air conditioner brands and models hold up better in harsher conditions than others. If you own a home, it's best to look at your user's manual to determine if your window unit requires any specific winter accommodations, or if it's recommended to leave it uncovered.

Why Do Air Conditioners Have To Be In A Window?

If you don't have a central air conditioning system, window air conditioners, and portable air conditioners offer you a great option to stay comfortable during the warmer seasons. Window air conditioner units are specially made to operate only when mounted in a window. The same goes for portable air conditioners, which require access to a window to connect the exhaust pipe that funnels air out of the window.

Air conditioner units expel water and warm air as by-products of their air cooling processes, and there isn't a way to redirect these by-products unless you drill a hole in the wall specifically to do so. And having the air circulating inside the home would be both illegal and unsafe for humans and animals.

Can Window AC Units Be Left In Winter?

Window air conditioner units can be left in the window during the winter season. Today's air conditioning units are designed to withstand cold weather conditions. However, long periods of extremely harsh weather can definitely reduce the lifespan of the unit. If you live in an apartment building, you really don't have an option not to leave the unit during the winter.

On the other hand, if you're a homeowner and living in an area where winters can be harsh, it is best to remove the unit and store it for the winter. Frigid outside temperatures will cause already formed condensation inside the unit to freeze. This can cause the coils on the unit to freeze, which will result in severe damage to the air conditioner.

However, the ice on the coils will often unthaw during the day due to heat from direct sunlight (and when it's at least 32 degrees Fahrenheit outside).

How Do You Winterize A Window Air Conditioner?

Window air conditioner units can take a beating in the winter, depending on your location. However, winterizing your A/C unit can help protect it from extreme weather conditions and, as a result, increase its lifespan. Let's look at how to do this in five simple steps:

1. Turn the unit off

Simply press the power button on your unit or lift the control panel and turn the unit off. Powering off your unit will prevent it from automatically powering on during an unseasonably warm day, which may cause the A/C unit to freeze up once the temperature drops again.

2. Give it a quick wash

You can take a large spray bottle or a garden hose to rinse off the exterior of your air conditioner. Doing so will remove any collected dust or debris. If your unit is especially dirty (sometimes they can collect dust and pollen), you can use a mild soap or detergent to clean it off. Afterward, be sure to rinse it off and check for any clogged up holes or crevices.

3. Re-Insulate The Window

Use weather seal or foam insulation to close up any spaces around your window unit. Do a careful inspection of the side panels, overhead ventilation area, the window jam, and the unit mount to locate any possible areas of air loss. If there are gaps in between the air conditioner and the seal of the window, air can pass through, causing energy losses of up to 20% during winter months, which means a higher heating bill.

Check out this foam insulation on Amazon.

5. Place A Cover Over The Unit

Next, cover the entire air conditioner with a breathable cover. Be sure to get your air conditioner unit measurements before purchasing the cover to ensure that you have the right size. If you live in an area where winds can be fierce in the winter, you may also want to purchase duct tape to help secure the cover to the unit.

Many covers also come with the added benefit of insulating the window in which the air conditioning unit is installed. This helps keep frosty breezes from blowing in the unit during cold winter days, which can reduce your utility bills low during these months.

Check out this window cover on Amazon.

Summing Things Up

Window A/C units can freeze up just like other HVAC systems, which can be caused by various factors. If you find that your unit has frozen up, it's best to contact a licensed professional to provide the proper diagnosis and get your unit up and running as soon as possible.

Interested in learning more about how to solve common HVAC problems? If so, be sure to check out our other posts:

Should Air Conditioners Be Covered In Winter?

Does Air Conditioning Add Moisture To The Air?

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