F9
MrCool
Defrost Protection / Outdoor Coil Low Temperature Abnormality
Indoor unit shows F9; system may not defrost properly or may shut down in heat mode.
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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
Faulty outdoor coil sensor, Defrost control issue on outdoor PCB, Severely iced outdoor coil, Low refrigerant charge
How to Fix / Troubleshooting
Safety first: Turn off power at the outdoor disconnect.
Steps:
- Inspect outdoor coil: Check the outdoor coil for heavy ice buildup. Light frost is normal; thick ice blocking airflow is not.
- Clear obstructions: Remove snow, leaves, or debris around the unit.
- Sensor check: Inspect the outdoor coil sensor (T3) for proper attachment and intact wiring.
Technician tasks: If F9 continues, a technician should test the defrost cycle, sensor resistance, and refrigerant charge, and may need to replace the outdoor PCB or sensor.
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Repair Difficulty
Hard
4/5
Required Part
Outdoor Coil Temperature Sensor (T3)
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