System and method of transferring refrigerant with a discharge pressure

A method to recover refrigerant for use in a heating/defrost mode of a transport refrigeration unit, comprising:

• during a refrigerant recovery operation of the heating/defrost mode, isolating a condenser coil from a discharge port of a compressor of the transport refrigeration unit by closing a condenser inlet solenoid valve that directs refrigerant from the discharge port to the condenser coil when open;
• during the refrigerant recovery operation of the heating/defrost mode, isolating a heating/defrost branch of the transport refrigeration unit from a discharge port of the condenser coil by closing a hot gas line solenoid valve that directs refrigerant, via a hot gas line, from the discharge port to a heating/defrost branch including an evaporator coil when open;
• and
• during the refrigerant recovery operation of the heating/defrost mode, directing refrigerant to flow from the discharge port of the compressor to a liquid refrigerant section of the transport refrigeration unit via a bypass line while preventing the refrigerant from flowing from the discharge port of the compressor to the condenser coil and preventing the refrigerant from flowing from the discharge port of the compressor to the heating/defrost branch including through the evaporator coil via the hot gas line.

A transport refrigeration unit, comprising:

• a compressor including a suction port and a discharge port;
• a condenser coil including a condenser inlet and a condenser outlet, the condenser inlet connected to the discharge port through a condenser inlet solenoid valve and the condenser outlet equipped with a condenser outlet check valve configured to prevent refrigerant flowing back to the condenser coil through the condenser outlet check valve;
• a liquid refrigerant section connected to the condenser outlet of the condenser coil;
• a bypass line connecting the discharge port to the liquid refrigerant section, the bypass line including a bypass line solenoid valve;
• a liquid to hot gas line connecting a liquid line to a hot gas line, the liquid to hot gas line including a liquid to hot gas line solenoid valve;
• and
• a check valve on the liquid to hot gas line configured to prevent refrigerant from flowing from the hot gas line to the liquid line;
• wherein when the transport refrigeration unit is in a refrigerant recovery operation in a heating/defrost mode, the condenser inlet solenoid valve is configured to be in a closed state, and the bypass line solenoid valve is configured to be in an open state so as to direct refrigerant discharged from the discharge port to the liquid refrigerant section,
• wherein when the transport refrigeration unit is in the refrigerant recovery operation in the heating/defrost mode, the liquid to hot gas line solenoid valve is configured to be in an open state so as to allow refrigerant from the liquid refrigerant section to flow to an evaporator coil through the liquid to hot gas line.