A system comprising: a compressor connected to an evaporator; a suction temperature sensor (34, 35) that outputs a suction temperature signal corresponding to a temperature of refrigerant entering said compressor; an ambient temperature sensor that outputs an ambient temperature signal corresponding to an ambient temperature; an inverter drive connected to said compressor that receives electric power and modulates a speed of said compressor by modulating a frequency of said electric power, where the suction temperature sensor (34, 35) is located at an inlet of said inverter drive; a heat sink temperature sensor located at an outlet of said inverter drive that outputs a heat sink temperature signal corresponding to a temperature of a heat sink associated with said inverter drive; a control module connected to said inverter drive that receives said suction temperature signal and said ambient temperature signal, that monitors compressor power data and compressor speed data from said inverter drive, that calculates a saturated evaporator temperature of a refrigeration system associated with said compressor and said evaporator based on said suction temperature signal, said heat sink temperature signal, said compressor power data, and said compressor speed data, that calculates a suction superheat temperature based on said suction temperature signal and said saturated evaporator temperature, calculates a discharge superheat based on said ambient temperature signal and said calculated suction superheat temperature; and that generates at least one of a control signal and a notification signal based on said calculated discharge superheat. a compressor connected to an evaporator; a suction temperature sensor (34, 35) that outputs a suction temperature signal corresponding to a temperature of refrigerant entering said compressor; an ambient temperature sensor that outputs an ambient temperature signal corresponding to an ambient temperature; an inverter drive connected to said compressor that receives electric power and modulates a speed of said compressor by modulating a frequency of said electric power, where the suction temperature sensor (34, 35) is located at an inlet of said inverter drive; a heat sink temperature sensor located at an outlet of said inverter drive that outputs a heat sink temperature signal corresponding to a temperature of a heat sink associated with said inverter drive; a control module connected to said inverter drive that receives said suction temperature signal and said ambient temperature signal, that monitors compressor power data and compressor speed data from said inverter drive, that calculates a saturated evaporator temperature of a refrigeration system associated with said compressor and said evaporator based on said suction temperature signal, said heat sink temperature signal, said compressor power data, and said compressor speed data, that calculates a suction superheat temperature based on said suction temperature signal and said saturated evaporator temperature, calculates a discharge superheat based on said ambient temperature signal and said calculated suction superheat temperature; and that generates at least one of a control signal and a notification signal based on said calculated discharge superheat.