Safety first: Turn off cooling at the thermostat and shut off power to the indoor unit if the coil is iced.

Step 1 – Thaw the coil: Set the thermostat to FAN ONLY and leave it running for several hours until all ice melts. Place towels under the air handler if needed.
Step 2 – Replace filter: Install a new, properly sized air filter. Avoid overly restrictive high-MERV filters unless the system is designed for them.
Step 3 – Check registers: Open all supply and return registers fully. Remove furniture or rugs blocking airflow.
Step 4 – Clean evaporator coil: With power off, remove the coil access panel. If the coil is matted with dust, gently brush and vacuum the surface. For heavy buildup, use a non-rinse evaporator coil cleaner following label directions.
Step 5 – Verify blower operation: Ensure the blower runs at the correct speed in cooling mode. If it is slow or intermittent, the blower motor or control board may need service.
Step 6 – Professional refrigerant check: If F3 recurs with good airflow, a technician should check refrigerant charge and system pressures.

Keeprite system shows F3 and cooling is disabled; may be associated with coil freeze or low airflow.

Possible Causes