A transport refrigeration unit is provided and includes a compressor, a condenser, an expansion valve, an evaporator, piping fluidly coupling the compressor and the condenser, a fluid loop to produce heated fluid from an engine, which is configured to drive operations of the compressor, a heat exchanger disposed in the refrigeration cycle such that the heated fluid thermally interacts with refrigerant of the refrigeration cycle and a hot gas bypass valve to control a quantity of refrigerant removed from the piping.