A transport refrigeration unit includes a combustion engine system having a turbo-charger constructed and arranged to receive air in a cold state and expel the air in a compressed hot state, an evaporator, and a defrost heat exchanger constructed and arranged to receive the air in the compressed hot state and expel the air in a compressed cooled state for defrosting the evaporator. In operation, the unit may be capable of controlling a defrost temperature and/or controlling the temperature of the air entering a combustion engine of the engine system for combustion by controlling the volume of air flow between the defrost heat exchanger and a charge air cooler of the engine system.