Dehumidifier displays E4 and shuts down or never starts the compressor.

Safety first: Disconnect power. Coils and metal brackets may be sharp; wear gloves.

Steps:

• 1. Confirm ambient conditions: If the unit is used in a very cold space (below Carrier’s minimum operating temperature), E4 may indicate low-temperature lockout rather than a failure. Move the unit to a warmer area and retry.
• 2. Locate defrost sensor: On many Carrier dehumidifiers, the defrost sensor is attached to the evaporator coil outlet or suction line. Identify the sensor or thermostat and its wiring.
• 3. Inspect wiring and mounting: Ensure the sensor is firmly attached to the tubing and that wires are not broken or chafed. Reseat the connector at the main board.
• 4. Test sensor/thermostat: Use a multimeter to check continuity (for a thermostat) or resistance (for a thermistor). Compare readings to Carrier specifications. A sensor that reads open or shorted at room temperature is likely defective.
• 5. Replace faulty component: Install the correct Carrier defrost sensor or thermostat. Secure it tightly to the tubing with the original clip or strap and insulate if originally insulated.
• 6. Check control board: If sensors test good, the defrost circuit on the main control board may be faulty. Replace the board if E4 persists after sensor replacement.

Note: Do not bypass defrost protection; doing so can cause severe coil icing and compressor damage.