Some causes of an air conditioning unit freezing up include a dirty air filter, a blocked vent, a broken fan and low refrigerant levels. Most of these problems are easy to fix; however, blocked vents and pipes may require a professional.
When an air filter is dirty, dirt in the filter can block airflow into the unit. When an air conditioner starts freezing, take a look at the filter before inspecting the rest of the unit. Changing a dirty filter can often fix the problem. Changing filters once a month can also prevent freezing from occurring.
Blocked vents and pipes are also common causes of freezing in AC units, as these can also interrupt airflow within the system. A broken blower fan can also prevent air from sufficiently circulating through the system. If these problems occur, call a professional heating and air conditioning specialist to repair the unit.
AC units use a refrigerant chemical called Freon to cool the air that runs through the system. Low levels of Freon cause low pressure within the unit, which results in freezing. Restoring the unit's Freon levels can fix the problem.
To prevent freezing from occurring, avoid using the air conditioner in cooler temperatures. Generally, air conditioners are designed to operate above 62 degrees Fahrenheit. Operating the unit at cooler temperatures can cause drops in pressure within the system, which in turn cause freezing. Homeowners should also ensure that their AC units are clean and well maintained.