Indoor unit shows E4 and system stops or runs briefly then shuts down, often during heating or defrost on heat pump models

Safety: Disconnect power at the outdoor disconnect and indoor breaker. Allow the unit to cool before touching refrigerant lines.

Steps:

• Access compressor compartment: Remove the service panel on the Comfortmaker condenser/heat pump.
• Locate discharge sensor: It is usually strapped or clipped to the small-diameter hot gas line leaving the compressor, with two wires to the PCB.
• Check attachment: Ensure the sensor is firmly in contact with the discharge line and secured with a clamp or tie. Re-secure if loose.
• Inspect wiring: Look for burnt insulation, rubbing on metal edges, or loose connectors. Repair or replace damaged sections.
• Measure resistance: Disconnect the sensor and test with a multimeter. Compare to manufacturer resistance values. Replace if out of spec.
• Replace sensor if faulty: Install a new Comfortmaker-compatible discharge temperature sensor and secure it tightly to the discharge line with thermal paste if provided.
• Reassemble and test: Restore power and run the system. Verify that E4 clears and the unit operates through a full cycle.

Note: If E4 recurs with a good sensor, there may be a refrigerant or compressor issue causing actual over-temperature; this requires a licensed HVAC technician.