Patent ID: 8734125

Claim:
A system comprising: a compressor including a shell housing a compression mechanism driven by an electric motor in an on state and not driven by the electric motor in an off state; a variable frequency drive that drives the electric motor in the on state by varying a frequency of a voltage delivered to the electric motor and that supplies electric current to a stator of the electric motor in the off state to heat the compressor; a control module connected to the variable frequency drive that controls a speed of the electric motor in the on state and that controls the electric current supplied to the stator of the electric motor in the off state; a compressor temperature sensor that generates a compressor temperature signal corresponding to a compressor temperature; wherein the stator heats the compressor for a first time period and the control module receives the compressor temperature signal, determines a rate of change of the compressor temperature over a second time period, after the first time period, and calculates an amount of current to supply to the stator based on the rate of change.