Quick answer
An evaporator coil freezes when it gets too cold, usually because of low airflow (a clogged filter, dirty coil, failing blower or closed vents) or low refrigerant from a leak. Switch the system to fan only to thaw it, then have the cause found, or it will freeze again within a day or two.
Written by Sylvia Denton, HVAC Guides Editor. Updated 2026-09-22.
The evaporator coil is supposed to run cold, around 40 degrees, so it can pull heat and moisture out of the air passing over it. If not enough warm air crosses the coil, or there is not enough refrigerant in it, the coil temperature drops below freezing. The water condensing on it turns to ice, the ice blocks more airflow, and the problem feeds itself until the coil is a solid block.
You usually notice it as weak or no airflow from the vents, frost on the copper line at the outdoor unit, or water pouring out of the air handler when the ice finally melts. In Miami, where the coil is handling huge amounts of moisture, a frozen coil also means a lot of water heading for a drain pan that may not keep up.
The fix is never just the thaw. We work through airflow first, because it is the most common cause, then refrigerant charge, then the controls that tell the system how fast to run.
