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Why does my AC unit keep freezing up?


This is a common problem, and often homeowners don’t realize it can be harmful to your air conditioner. If your unit is freezing up, it needs to be serviced. There are a few main causes:

  1. Your air filter is extremely dirty. If you suspect this is the problem, turn off your system. Do not make the mistake of changing the air filter and turning the unit right back on. If you have seen ice, it will take 4-8 hours to completely thaw. If the air filter was the issue, and it is not thawed out, the unit will continue to freeze. Just because ice has melted on the outdoor unit does not mean the machine has thawed. The ice starts in the evaporator coil (inside your attic) and then travels down the refrigerant lines to the outdoor unit. You cannot see your evaporator coil, it is inside of the indoor unit. If there is ice outside, the evaporator is a complete block of ice inside.
  2. Stuck contactor in the outside unit. This can happen when it becomes “pitted” due to usage and age. It can weld itself together and the outdoor unit never stops running. When the indoor unit stops running, the system will immediately start to freeze because there is no airflow. Contactors are like spark plugs on cars, they do not last forever. We check contactors on our tune up and maintenance visits, if they are showing signs of wear, we suggest replacing the part.
  3. Failed indoor blower motor. If the blower fails, not airflow is present. Many things can cause the motor to stop working. Sometimes it is the motor itself, other times there is something that is causing it not to run. Turn off your unit and call for AC repair immediately.
  4. Low refrigerant (Freon) charge. This requires a qualified technician to diagnose. If you air conditioning system is low on charge, there is a good possibility it is leaking. A technician can check for a leak and help with a solution.
  5. Bad thermostat. If the thermostat control is not sending the correct signals to the indoor and outdoor unit, it can result in your AC freezing up. Call for service and have a technician figure out what’s going wrong.
  6. Some sort of airflow restriction. Possibly some insulation loose somewhere in the system. A service person would need to take apart the indoor unit to diagnose if that is the problem.

This list is limited, but covers the most common situations that could make your AC system freeze up. Call Harris Air Services today if you are experiencing any of these issues! 469-325-1034

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