Indoor unit control board flashes F1, blower may not start or runs erratically in cooling mode

Safety first: Turn off power to the furnace/air handler at the breaker. Electronic boards are sensitive to static—ground yourself before touching.

Steps:

• 1. Power reset: Turn off power for at least 5 minutes to allow capacitors to discharge. Restore power and see if F1 clears.
• 2. Inspect board connections: Remove and reseat all multi-pin plugs and terminal strips on the indoor board. Ensure no pins are bent.
• 3. Check for moisture or corrosion: Look for water stains, rust, or insect damage on the board. Address any water leaks from the coil or drain pan.
• 4. Verify correct line voltage: Have a qualified person confirm that the indoor unit is receiving the correct supply voltage and that there are no frequent brownouts.
• 5. If F1 persists: The control board’s memory is likely corrupted. Replacement of the indoor control board is typically required and may involve configuration steps best handled by a technician.