· Michael Blair
Ice on the indoor coil or the line set during a Middle Tennessee August feels like a contradiction. It happens because a coil that is not absorbing enough heat drops below freezing and condenses moisture out of our very humid air, which then freezes solid.
Airflow first, and it usually ends there
A clogged filter is the single most common cause. Restricted air across the coil means less heat picked up, so the coil temperature falls and Nashville humidity does the rest.
Closed or blocked supply registers, a collapsed flex duct and a dirty blower wheel all do the same thing. If more than one room is affected, suspect the equipment; if one room is, suspect the duct to it.
Then the coil itself
An evaporator coil coated in dust insulates itself from the air passing over it. The symptom develops slowly over years and often shows first as longer run times before it becomes visible ice.
Coils are behind the filter for a reason. A coil that is dirty despite a maintained filter usually means the filter has been the wrong size or seated badly, letting air bypass it.
Refrigerant, and what low means
Low refrigerant lowers the pressure in the coil, which lowers its temperature, which freezes it. But refrigerant is a sealed system — it is not consumed. Low charge means a leak.
A contractor who tops it up without finding the leak is selling you the same repair next summer. Ask for the leak to be located, and get a number for the recharge separately from the repair.
- Change or correctly seat the filter
- Open and unblock every supply register
- Check the coil for dust build-up
- Look for oily residue at joints, a sign of a refrigerant leak
- Confirm the outdoor unit is not blocked by growth
What to do while it is frozen
Turn the cooling off and the fan on. That moves house air across the coil and thaws it far faster than switching everything off, usually within one to three hours.
Do not run cooling while iced. The compressor risks taking liquid refrigerant back, which is the failure that turns a filter problem into a compressor replacement.