Room AC, humidifiers & heaters

Window AC has ice on the coils

Ice usually forms when airflow across the cold coil is restricted or the outdoor temperature is too low for the unit to run properly, so warm moist air keeps freezing on contact.

Difficulty
Easy
Time
1–3 hours (mostly thawing time)
DIY cost
$0–$15
Pro cost
$100–$300

Symptoms

  • Visible frost or ice on the coils behind the filter
  • Weak or no airflow
  • Water pooling as the ice melts
  • Unit runs but barely cools

Likely causes

  • CommonDirty air filter blocking airflowRestricted airflow lets the coil get too cold and frost over.
  • CommonRunning the AC when outdoor temps are too low (below roughly 60F)Low outdoor temperatures make the refrigerant run too cold for normal airflow to keep the coil above freezing.
  • PossibleLow refrigerant chargeReduced pressure can cause abnormally cold coils and icing even with good airflow.
  • PossibleFan motor running too slowly or failingWeak air movement over the coil lets frost build even with a clean filter.

What to do

  1. Turn the unit off completely and switch the fan to fan-only mode (no cooling) until all the ice melts, which can take a few hours.
  2. Once thawed, remove and clean the filter, then check for anything blocking the front intake or vents.
  3. Avoid running the AC in cooling mode when it's cool outside (below about 60F); use fan mode instead.
  4. Restart the unit in cooling mode and watch the coil after 30–60 minutes to see if frost returns.
  5. Listen to the fan for weak or rattling sound that suggests a slow motor.
  6. If ice returns quickly with a clean filter and normal outdoor temperature, the unit likely needs a refrigerant or motor inspection.

Tools and parts

  • None
Replacement window AC filterSearch: “window air conditioner filter”

When to call a pro

Call a technician if ice keeps returning despite a clean filter and reasonable outdoor temperatures, since that points to low refrigerant or a fan motor problem.

Safety

Generally low risk

Generally low risk for a careful person. Stop if anything looks different from what this guide describes.

Related guides

Operator provides AI-generated troubleshooting information. It can be wrong. For safety-critical, electrical, gas, structural, medical, automotive safety, or other high-risk problems, consult a qualified professional.