Abstract: A method of controlling a compressor in a transport temperature control unit having a prime mover providing power to the compressor. The compressor has a power requirement that varies depending on loading conditions. The method includes determining the maximum power available from the prime mover, determining the power requirement of the compressor, and adjusting the loading conditions of the compressor so that the power requirement of the compressor substantially equals the maximum power available from the prime mover. Preferably, the method includes starting the compressor at a low speed, varying the suction pressure as permitted by the maximum amount of power available until the suction pressure reaches a maximum suction pressure setting, and after the suction pressure reaches a maximum suction pressure setting, increasing the speed of the compressor as permitted by the maximum-amount of power available.