Air Conditioners Not Cooling; Cold Outdoor Temperatures
Operating a room air conditioner if the outdoor temp is 70F or below will limit the cooling capacity of the unit. Under these conditions it is possible for the indoor coil to frost or freeze over, limiting cooling performance. The further the temperature drops below 70F the less productive it becomes. This will not usually harm the unit, but wastes energy.
In many cases, outdoor temperatures of 50F or less will cause the compressor to not come on, depending on the indoor temperature. If the outdoor temperature falls to 32 F or below, any water left in the exterior pan of the unit will freeze.