If your home's air conditioner is running but pumping warm air, or it stops working for a couple of hours at a time but runs again after sitting for a few hours, that's a good indication that your air conditioning unit is freezing up. If you've never dealt with this before, there are some things that you should know. Here are some of the most common causes of air conditioner freezing and what you should do about them.

Poor Air Circulation

One of the most common reasons for an air conditioning system to freeze up is a lack of airflow around the evaporator coils. When your air conditioner isn't circulating air as it should, the colder air remains around the evaporator coils and causes freezing. If you haven't changed your air conditioning unit's air filter in a while, this could be what has caused the problem.

When an air filter gets dirty, air can't flow through it the way that it should. This leads to poor airflow and freezing around the evaporator coils. Shut the system down for a couple of hours so that it can thaw out. Clean the evaporator coils and replace the air filter. This should restore your unit's functionality. If not, you'll need to call for further repair.

Low Outdoor Temperatures

If you run your air conditioner when the temperatures outside are too cold, the cold air coming in the intake of the air conditioner can cause the unit to freeze. Every air conditioner is rated for a certain temperature range. Make sure that you know what the coldest outdoor temperature is that your air conditioner will function within so that you do not inadvertently try to run the unit when it is too cold for safe operation. 

In the event that you do this, you should have your air conditioner inspected by a repair technician as soon as possible to be sure that the cold weather didn't do any further damage to the components inside the system.

Refrigerant Leak

In an ideal situation, your air conditioner will maintain a closed system status so the refrigerant that flows through the coils stays consistent. However, if you experience a refrigerant leak, that can drop the levels over time. 

The lower level of refrigerant causes the evaporator coils to operate at a lower temperature. This can allow excess condensation to form inside the unit. That condensation will start to freeze on the coils, causing ice buildup inside the system.

If you have eliminated the air filter and the outdoor temperature as the causes of your freezing air conditioner, you may have a refrigerant leak. Contact a residential air conditioning repair technician right away and shut your system down until it can be repaired.