F9
Comfortmaker
Power Supply / Voltage Abnormality
Display shows F9 and system may not start or may shut down unexpectedly
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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
Low or high line voltage, Loose line connections at contactor or breaker, Shared circuit with heavy loads, Defective power supply section of control board
How to Fix / Troubleshooting
Safety: Only check voltage if you are trained and have a proper meter. Otherwise, call an electrician or HVAC technician.
Steps:
- Inspect connections: With power off, tighten lugs at the Comfortmaker disconnect, contactor, and breaker.
- Check dedicated circuit: Ensure the AC is on its own breaker and not sharing with other large loads.
- Measure voltage: With power on, verify voltage is within the nameplate range (typically 208–230V for residential units).
- Install surge protection: Consider adding a surge protector to protect the control board.
Note: Persistent F9 with correct voltage suggests a failing control board power supply.
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Repair Difficulty
Hard
4/5
Required Part
Outdoor Control Board (Power Section)
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