Why Air Conditioners Freeze Up

First, it’s important to understand why air conditioners freeze over. An air conditioning unit needs proper air flow in order to keep the coil warm. The air from inside your home is needed to circulate through the unit, keep the coil cold, and keep the temperature above freezing. If this does not happen correctly, the coil is going to freeze before any condensed water is drained away from the air conditioning unit. So basically, if there is a blockage of the airflow, then it is likely that the unit will freeze over. Here are some causes of poor airflow:

  • Having an air filter that is dirty.
  • Registers or air vents that are closed can also cause unit freeze ups.
  • Low refrigerant levels can result in cold coils.
  • Improper fan operation or a faulty fan can prevent air from moving like it should be.
  • A faulty thermostat can misread the temperature and keep the unit cooling.
  • Drainage problems can also cause the unit to freeze. An air conditioning unit condenses water vapor into liquid that drains outside. If the coils are frozen, ice is going to cause a blockage for the drain hole. The unit is still going to run, but it is not going to cool properly and it is going to use a lot more electricity. If you run an air conditioning unit with frozen coils, it is going to lead to extensive damage of the compressor, which is the most expensive part of an air conditioning unit.

What to Do About a Frozen Air Conditioner

What you need to do about your frozen air conditioner will depend upon why the unit is freezing up.

  • Always checks the unit’s air filters and make sure they are clean and replace them if needed.
  • Always make sure that all registers and air vents are clear and open.
  • Replace faulty thermostats, if you notice they are not working correctly.
  • Check the outdoor unit’s drain pipe for any blockages of debris and twigs and clear all debris.
  • If you are unable to fix the frozen coil problem yourself, it is best to call a certified technician as soon as possible.

Signs of Something Worse

If you have tried all of the above and your system is still freezing up, you need to call a professional to come out and fix your problem. There may be a leak in the coolant. An HVAC professional can insert a dye into the coolant tubing to locate any possible leaks. In the meantime, turn off the unit and allow the coils to defrost. You can manually apply some salt or salt water to the coils to aide them in defrosting faster.


Just like scheduled maintenance on your vehicle, it is equally important to do yearly inspections on your air conditioner. Getting maintenance completed will not only keep your air conditioning from freezing up but will increase the longevity of your unit and help you be able to fix your unit before summer hits. Air conditioner units are very expensive. Any yearly maintenance costs are going to save you a lot of money in the long run.