E4
Fraser-Johnston
High Discharge Temperature / Compressor Overheat Protection
E4 displayed, unit stops and may restart after a delay
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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 refrigerant charge causing compressor overheating, Blocked or dirty condenser coil, Failed discharge temperature sensor, Non-operational outdoor fan motor
How to Fix / Troubleshooting
Safety: Turn off power at the disconnect before opening the outdoor unit.
- Check outdoor fan and coil: Confirm the outdoor fan runs whenever the compressor is on. If not, test and replace the fan motor or capacitor as needed. Clean the condenser coil thoroughly.
- Inspect discharge sensor: Locate the discharge line thermistor on the compressor discharge line. Ensure it is tightly clamped and not damaged. Replace if cracked or if resistance is out of spec.
- Verify airflow indoors: Poor indoor airflow can also cause high discharge temperature. Check indoor filter and blower operation.
- If E4 repeats: A refrigerant issue (undercharge, overcharge, or restriction) may be present. Have a licensed technician check superheat/subcooling and correct charge.
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Repair Difficulty
Hard
4/5
Required Part
Discharge Line Temperature Sensor
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