One of the most common causes of an air conditioner freezing up is insufficient airflow through your evaporator coil. This can be caused by something as simple as a blockage, such as a plugged up air filter that prevents good airflow back to your system, or a malfunction that causes the evaporator fan (or “blower”) to stop working. Air conditioning relies on refrigerant being converted from a liquid state back into a gas in the evaporator coil (this is the “indoor coil” that sits on top of the furnace or handler in most systems). As the evaporator fan blows air across the indoor coil, the liquid refrigerant absorbs the heat from the air, thus cooling it as it is recirculated back through your home.
This process also causes the refrigerant to evaporate, changing it back into a gaseous state and allowing it to continue back through the refrigerant “loop”. If the evaporator fan is not working, the heat in the air is not being transferred to, and carried away by, the refrigerant. This will cause the coil to freeze up and will prevent your air conditioning system from doing its job.
There are a number of things that can cause the evaporator fan to stop working:
- The blower motor (evaporator fan motor) may have failed.
- The fan relay may have failed, causing the blower motor to not operate.
- Your thermostat may have failed, causing the blower motor to not operate or the compressor in your air conditioner to not shut off.
- The compressor relay in your air conditioner may have frozen, causing the compressor to never stop running.
Other potential causes of your air conditioner freezing up can be an improper refrigerant charge in your system’s condensing unit or excessively low outdoor temperatures. These are just a small number of potential causes that would result in your air conditioner freezing up.
If your air conditioner is freezing up, shut off your air conditioning system and allow it time for all of the ice to melt. Be sure to check your air filter as well, since a dirty filter can reduce the airflow required for the system to operate correctly. Once it has “thawed”, you can turn the system back on to see if it is functioning normally. If the problem persists, contact a trained HVAC Contractor in your area.
Modern air conditioning systems have fairly complex electrical and mechanical control systems which prevents most of us from having the technical skills to diagnose and repair them ourselves. For this reason, it is always recommended to use a qualified Air Conditioning Contractor instead of attempting to make your own repairs.