Honeywell AC shows F4 and may not operate in heat or cool mode (for heat pump models).

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.

Possible Causes

Open or shorted discharge line sensor, Sensor wiring damaged by heat, Loose connector at PCB, Failed sensor input on control board

Safety: Disconnect power. Components near the compressor and discharge line can be very hot; allow cooling time.

Steps:

Locate discharge sensor: On heat pump models, find the sensor attached to the compressor discharge line or outdoor coil.
Inspect sensor and wiring: Look for heat-damaged insulation or loose mounting. Reattach sensor firmly to the line or coil.
Test sensor: Measure resistance and compare to specifications. Replace if open, shorted, or out of range.
Check PCB: If a new sensor does not clear F4, the control board may need replacement.

Hard 4/5

Discharge Line Temperature Sensor

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