When you notice ice building up on your air conditioner, it's never a good sign. Freezing occurs when condensed water isn't evaporated away from the cold coil inside the air conditioner. There are several reasons this could occur, so do some troubleshooting before you contact a technician or attempt to repair the problem.
Let the Air Conditioner Rest
Switch your air conditioner off or put it on fan mode to give the unit a rest and allow the coils to fully defrost. The bulb that senses the coil temperature normally turns off the compressor when coils drop below 36 degrees to prevent freezing. Sometimes when an AC unit is put on its highest setting, this feature is disabled and the coils can ice up. You may be able to avoid freezing by changing this setting.
Check the Refrigerant
Look for leaking refrigerant dripping from your air conditioner. When there isn't enough refrigerant, the evaporator coil will not work properly and moisture will build up in the system. A professional will need to come to your home to recharge the unit and can also help determine where there is a leak.
Clear the Air Flow
Check for obstructions like dirt on the unit or damage to the vents. Clean or change the filter, scrub the exterior and remove dust using a vacuum to remove dirt that could be restricting airflow. If the fan still isn't blowing enough air over the coils to keep them dry, the fan motor or capacitor might need to be repaired or replaced.
Examine Other Important Components
There are several other essential parts that could be causing an issue. Check your unit's liquid line for a clogged filter or strainer, which can cause premature expansion. If the unit has a thermal expansion valve, it may need to be readjusted. You might also want to readjust the evaporator pressure regulator. If the pressure is too low, moisture will be left in the system and could freeze. A stuck compressor contact could also be preventing your system from shutting off automatically, causing the unit to become overworked.
Compare BTUs and Room Size
Ask an HVAC expert or compare your square footage to the BTU output to determine if your unit is up to the task of cooling your home. Your air conditioner may not be powerful enough to cool the space that you have, which means it's working constantly. Frost could be forming because the unit is overworked and extra moisture is continually forming.
Learn more about AC units in the air conditioner buying guide