A transport refrigeration unit (26) includes a dedicated combustion engine system (56), an evaporator (50), and a de-frost heat exchanger (78) constructed and arranged to flow engine coolant in a heated state for defrosting the evaporator (50) when the dedicated combustion engine system (56) is not running. A method of operation may include running a defrost cycle of the unit (26) utilizing the heated coolant whether or not an associated internal combustion engine (66) of the unit (26) is running.