Oh, this a call we get a lot. It’s a pretty common problem with central heating and air systems. Most of the time, homeowners will say, "I need Freon, my unit keeps freezing up." And while that could be the case, it could be a simpler problem and you may not even need a service call. Just in case you've never encountered your air conditioner freezing up, let us give you a few things to look for.
The first thing to look for is ice. You may notice ice on the unit outside, especially where the two copper lines from the house go into the outdoor unit. Next look at the indoor coil. You may also notice that even though you hear the unit running inside the house, there is no air coming from any of the vents. If you notice any of these symptoms, turn off the system immediately. This will allow the coil and copper lines to begin to thaw.
There are a few things that will cause the system to freeze up. The first, you can check yourself and may save you some money on having to have a service call. The first thing to check is your air filters. Lack of air flow will cause the system to freeze up.
If your filters are dirty and have not been changed for a long period of time, that may have caused the issue. Just replace the filters with clean ones. Leave the system off for 3-4 hours to allow it to thaw.
Then turn the thermostat back on and continue normal operation. If the unit cools fine and does not freeze up again then you should be fine. Although it is good to have the system checked annually by a service professional.
The second thing would be a dirty indoor coil or blower wheel. If the filters have not been changed regularly or if the system has been running without filters, then dirt may have accumulated on the indoor coil and or blower wheel. This will slow down the air flow, causing the system to freeze up. The coil and blower wheel are not very easily accessible and you would need a service professional to check for this and make the repair.
The third thing and most often seen is a low refrigerant charge. When the refrigerant level gets low on an air conditioning system, the indoor coil will get too cold and start to freeze. It might not make sense that it would get too cold, but it does, and it creates ice.
If the filters and coils are clean then it’s probably refrigerant charge causing the issue. You would need a service professional to charge the system. You may have a leak and need to have the leak located and repaired or the system replaced.
The last thing and sometimes overlooked is setting the thermostat too low when temperatures are cool outside. If the outdoor temperature is below 70 degrees and you turn the thermostat down to 60 degrees, the system may run a long time to bring the temperature down and the pressures can get too low, causing the system to freeze. This is very common when it has been warm during the day and the temperatures drop very low at night - like during spring and fall.
So, if your system freezes up during this time of year, you may think back to whether you changed your thermostat to a lower setting than normal. And if so, did the outdoor temperature drop dramatically?
If yes, then you may be able to thaw the unit and return to normal operation. There are also low ambient controls that can be added to your system to keep the pressures from getting too low when running in cooler temperatures. These are used on commercial buildings regularly such as doctors offices and retail stores where the air conditioner runs even at very low outdoor temperatures.
So, if you do find that your air conditioner froze up, we hope these tips will help. Remember to turn your system off and let it thaw for 3-4 hours. Check your air filter, and if needed, call a service professional. It’s also a great idea to sign up for annual maintenance on your air conditioning system to greatly reduce the chance you'll ever need these tips at all.