Trane air conditioner shows E4 and shuts down; may be accompanied by ice on the indoor coil or very low airflow.

Safety first: Turn off power to the indoor unit at the breaker before removing panels.

• Replace filter: Locate the return air filter at the air handler or return grille. Replace with a clean filter of the correct size and MERV rating recommended by Trane.
• Open vents: Walk through the home and open all supply registers and return grilles. Remove rugs or furniture blocking airflow.
• Inspect blower: Remove the blower compartment panel. Check for heavy dust buildup on the blower wheel. Clean with a soft brush and vacuum if accessible. Verify the blower wheel is firmly attached to the motor shaft.
• Check blower start: Restore power and call for cooling. Confirm the blower starts immediately and runs smoothly. If it hums but does not start, the blower capacitor or motor may be failing.
• Thaw coil: If the evaporator coil is frozen, run the system in FAN ONLY for several hours until all ice melts, then resume COOL mode.

If E4 recurs after airflow corrections, a technician should check refrigerant charge and the evaporator temperature sensor.