After noticing that your home is not being cooled properly, you may have discovered ice on and inside your central air conditioning unit. Even after thawing out the unit, you may find that it keeps happening. Below are some reasons why your central AC unit is freezing up and possible solutions to the problem.

1.  Thermostat Is Set Too Low

When trying to determine what is causing your frozen air conditioner, take a look at both the temperature outside and the setting on your thermostat. If you are in the habit of keeping your thermostat lower than the exterior temperature, especially at night, you will most likely wake up to ice on the unit.

Even if the temperature is cooler outside, your AC unit will continue to work to maintain the thermostat setting. The combination of the cold air inside the unit and the cool air surrounding it will start to freeze any condensation. If this continues for hours, the frozen condensation builds up, forming ice that blocks of the vents of your unit.

If you see that the forecast calls for cool temperatures overnight, set your thermostat a couple of degrees above them. Since the air conditioner will not have to work as hard in a cooler environment, this should help keep it from freezing up.

2.  Airflow Is Blocked

If you usually do not keep your thermostat on a low setting, or if you have adjusted the temperature and still have a frozen air conditioner, the problem could be blocked air flow. If either the outer vents or the air filter is clogged, the cold air inside the unit will not be able to escape, creating frigid temperatures within the system that freezes any moisture.

To see if this is the issue, first either change or clean the air filter, depending on whether your unit uses disposable filters or reusable ones. Then, clean out any dust, mud, or debris from the vents to fully open them up. Also, look to see if any bushes or other plant life are blocking the vents, as these could also restrict air flow. 

After ruling out the setting on your thermostat and cleaning your AC unit, you may determine that the problem lies with a leaking refrigerant line or broken condenser. If so, contact an air conditioning repair service to have them inspect the unit and discuss your options for fixing it.