F4
York
High Temperature / Limit Switch Fault (Cooling Mode Airflow Issue)
York furnace/air handler board flashes F4 and system cycles off on safety
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Safety Warning
This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.
If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.
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Possible Causes
Severely restricted airflow, Dirty evaporator coil, Failed indoor blower motor, Faulty limit switch or rollout switch
How to Fix / Troubleshooting
Safety: Turn off power to the air handler or furnace. Some limit switches are near hot surfaces.
- Replace filters: Install new return air filters and ensure all supply registers are open.
- Inspect evaporator coil: Remove access panel and check the York A‑coil or slab coil for heavy dust or bio‑growth. Clean with approved coil cleaner.
- Check blower operation: Run the fan in ON mode. If the blower does not run or is weak, test the motor and capacitor (if PSC) or ECM module and replace as needed.
- Inspect limit switches: Look for manual‑reset rollout switches that may have tripped. If a rollout has tripped, do not reset repeatedly—find and correct the cause of overheating.
- If F4 persists: A technician should verify static pressure, duct sizing, and replace any faulty safety switches.
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Repair Difficulty
Hard
4/5
Required Part
Evaporator Coil
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