A method of defrosting a transcritical vapor compression system operable in a cooling mode and a defrost mode, the transcritical vapor compression system having a compressor for compressing a refrigerant, the compressor having a compressor inlet and a compressor outlet and operating at a first speed/frequency during the cooling mode, a first heat exchanger for cooling the refrigerant during the cooling mode, an expansion valve for decreasing the pressure of the refrigerant, the expansion valve having a variable opening, and a second heat exchanger for cooling a space during the cooling mode, the method comprising: directing a superheated refrigerant gas from the compressor to the first heat exchanger during the defrost mode, then directing the superheated refrigerant gas from the first heat exchanger to the expansion valve during the defrost mode, then directing the superheated refrigerant gas from the expansion valve to the second heat exchanger during the defrost mode; defrosting the second heat exchanger with the superheated refrigerant gas; and characterized in that the method further comprises: decreasing the speed/frequency of the compressor during the defrost mode to a second speed/frequency lower than the first speed/frequency and greater than zero; controlling the opening of the expansion valve during the defrost mode to maintain a superheated refrigerant condition proximate the inlet of the compressor; and providing a blower for selectively directing a fluid over the first heat exchanger; and turning off the blower or controlling the speed/frequency of the blower based on a pressure value proximate the outlet of the compressor so the pressure value does not exceed a predetermined maximum. directing a superheated refrigerant gas from the compressor to the first heat exchanger during the defrost mode, then directing the superheated refrigerant gas from the first heat exchanger to the expansion valve during the defrost mode, then directing the superheated refrigerant gas from the expansion valve to the second heat exchanger during the defrost mode; defrosting the second heat exchanger with the superheated refrigerant gas; and characterized in that the method further comprises: decreasing the speed/frequency of the compressor during the defrost mode to a second speed/frequency lower than the first speed/frequency and greater than zero; controlling the opening of the expansion valve during the defrost mode to maintain a superheated refrigerant condition proximate the inlet of the compressor; and providing a blower for selectively directing a fluid over the first heat exchanger; and turning off the blower or controlling the speed/frequency of the blower based on a pressure value proximate the outlet of the compressor so the pressure value does not exceed a predetermined maximum. decreasing the speed/frequency of the compressor during the defrost mode to a second speed/frequency lower than the first speed/frequency and greater than zero; controlling the opening of the expansion valve during the defrost mode to maintain a superheated refrigerant condition proximate the inlet of the compressor; and providing a blower for selectively directing a fluid over the first heat exchanger; and turning off the blower or controlling the speed/frequency of the blower based on a pressure value proximate the outlet of the compressor so the pressure value does not exceed a predetermined maximum.