Abstract: A heat pump refrigeration system has a refrigerant condition detector for detecting the mass of refrigerant in the system and initializing a refrigerant mass recovery operation. The heat pump system comprises three flow paths. When a cooling operation is performed, refrigerant flows in a first flow path through a compressor, outdoor heat exchanger, indoor heat exchanger, and the compressor, respectively. During a heating operation, refrigerant flows in a second flow path through the compressor, indoor heat exchanger, a refrigerant heater and the compressor, respectively. The system has a third flow path used during the refrigerant mass recovery operation. A controller causes the heating operation to continue in response to an appropriate signal from the condition detector. When the condition detector indicates an inappropriate refrigerant condition, the controller causes fluid to flow through the third flow path for a predetermined time period.