Room AC, humidifiers & heaters

Dehumidifier coils freezing over

Frost on the coil usually happens when the room is too cold for the unit's compressor cycle, or airflow across the coil is restricted, both of which are common in unheated basements.

Difficulty
Easy
Time
1–4 hours (mostly thawing)
DIY cost
$0–$20
Pro cost
$100–$250

Symptoms

  • Visible frost or ice on the coil behind the filter
  • Reduced or no water collection
  • Weak airflow from the unit
  • Frost worse in a cold basement or garage

Likely causes

  • CommonRoom temperature too low for a standard compressor dehumidifier (below about 65F)Standard units aren't designed to defrost properly in cold spaces; a low-temperature or 'basement' model is needed instead.
  • CommonDirty air filter restricting airflowLess air across the coil lets it get too cold and frost over.
  • PossibleBlocked intake or exhaust ventsFurniture or boxes placed too close to the unit reduce airflow.
  • PossibleFailed auto-defrost sensor or cycleSome units have a defrost feature that can fail, letting frost build unchecked.

What to do

  1. Turn the unit off and let the ice fully melt, which can take several hours; do not chip or scrape the coil.
  2. Clean or replace the air filter once thawed.
  3. Make sure there's at least a foot of clearance around the intake and exhaust vents.
  4. Check the room temperature; if it's regularly below about 65F, look for a dehumidifier rated for low-temperature or basement use.
  5. Restart the unit and monitor the coil after an hour for returning frost.
  6. If frost returns in a warmer room with clean airflow, the auto-defrost feature or refrigerant system may need service.

Tools and parts

  • None
Replacement dehumidifier filterSearch: “dehumidifier filter replacement”
Low-temperature basement dehumidifierSearch: “low temperature basement dehumidifier”

When to call a pro

Call an appliance technician if frost keeps forming in a reasonably warm room with good airflow, since that points to a refrigerant or defrost system fault.

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.