Error Code 21 — Indoor coil frosted

What does 21 mean?

The indoor unit's cooling coil has frozen over with ice. This can happen if there's not enough heat, the indoor temperature is too low, or airflow is blocked.

• Lack of heat in the conditioned space
• Operating indoor unit at excessively cold air temperatures
• Blockage of airflow to the indoor unit
• Issue with the indoor fan motor

Click steps to track your progress.

1. 1

   Ensure the system is set to the correct mode (heating or cooling) for the ambient conditions.

2. 2

   Check and clean the air filter of the indoor unit.

3. 3

   Verify that airflow to the indoor unit is not obstructed.

4. 4

   Allow the system to run in fan-only mode to defrost the coil, or turn the system off.

5. 5

   If the condition recurs, consult a technician.