Several air conditioner problems can cause it to ice up, including insufficient air flow, refrigeration problems and outdoor temperatures. Failure to resolve the ice buildup can permanently damage the unit.
If the air conditioner is experiencing a restriction in air flow, the temperature can drop below freezing. Specifically, the evaporator coil becomes extremely cold when the air is not properly able to escape. This is due to the humidity in the air. This moisture collects on the coil and, over time, turns to ice and greatly compromises the system's ability to produce cold air. Causes of air flow restriction include dirty air filters, obstructed air ducts, a damaged blower motor and dirt buildup on the evaporator coil itself.
Another potential cause of an ice up is due to problems with the refrigeration system. When refrigerant leaks, or there is an insufficient amount of refrigerant in the system, the pressure can drop in the evaporator coils. This causes moisture to accumulate on the coil and eventually freeze.
Finally, the outdoor temperature can affect the chances of an air conditioning unit icing up. Since most of these units are not able to function properly in an environment cooler than 60 degrees, overnight temperatures can greatly impact the device. When the system attempts to function in lower temperatures, freeze ups can occur.