Repair
Why the Air Conditioner Ices Over
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If the fat copper line at the outdoor unit is white with ice, or the coil is a solid block, turn the cooling off. The compressor is still trying to pump against that ice. Leave the fan on if the ice is on the indoor coil and you want it to thaw. Do not knock it off with a screwdriver. You will fold the fins, and you can crack the line.
The filter and the vents
Most of the time the air cannot get through. A filter you cannot see light through, a return covered by a rug, or half the supplies closed in rooms nobody uses. The coil gets colder than it was built to, and the water on it freezes. Put in the size printed on the old filter, open the vents, and wait until the ice is gone before you start cooling again.
A one-inch filter that looked fine at the start of a pollen week can be finished by the weekend. Hold it up to a window before you decide the refrigerant is gone.
If it ices again the same day
Filter new, vents open, and the line is white again that afternoon: the charge is low. Refrigerant does not get used up the way gasoline does. A low charge is a leak. Adding gas and leaving is how the same truck is in the driveway in August.
Ask them to look for the leak and to price that repair. A new system can be the second number on the page. If the house is still warm after the ice is gone, that is the same visit, not a separate sales appointment.
January is a different ice
A heat pump in real cold will frost the outdoor coil and then clear it. That is defrost, and it is normal when the coil comes back bare. A unit that stays a block of ice, or that defrosts every few minutes on a mild day, is not. That check sits with the older heat pumps. An air conditioner with ice on it in July is not defrosting. Turn the cooling off.