- Excessive refrigerant charge.
- Defective or leaking reversing valve (heating units).
- Low refrigerant charge.
- Condenser external unit coil (heating mode) or frozen internal evaporator unit (cold mode) coil.
- Insufficient air flow in the coil of the condenser external unit (heating mode) or coil of the evaporator internal unit (cold mode).
- Suction line clogged.
- Obstructed or frozen expansion device.
- Poor contact between the line and the defrost sensor (units with heating).
- Air flow in the condenser too high (in cold mode) in relation to external temperature.
