A compressor comprising: an intake passage; a discharge passage; a compression mechanism, the compression mechanism being positioned to receive vapor from the intake passage and provide compressed vapor to the discharge passage; a port positioned in the compression mechanism to bypass a portion of the vapor in the compression mechanism to the discharge passage; a valve positioned near the port to control vapor flow through the port; the valve having a first position to permit a first vapor flow from the compression mechanism to the discharge passage, a second position to permit a second vapor flow from the compression mechanism to the discharge passage and a third position to prevent vapor flow from the compression mechanism to the discharge passage; the compressor having a first volume ratio in response to the valve being in the first position, a second volume ratio in response to the valve being in the second position and a third volume ratio in response to the valve being in the third position, the first volume ratio being less than the second volume ratio and the the second volume ratio being less than the third volume ratio; at least one solenoid valve, the at least one solenoid valve being positioned to control a flow of fluid to the valve, wherein the flow of fluid to the valve determines the position of the valve;, characterized by a controller, the controller comprising a microprocessor to execute a computer program to energize and de-energize the at least one solenoid valve to control the flow of fluid to the valve and adjust the position of the valve in response to an operating parameter anda first solenoid valve and a second solenoid valve, the first an intake passage; a discharge passage; a compression mechanism, the compression mechanism being positioned to receive vapor from the intake passage and provide compressed vapor to the discharge passage; a port positioned in the compression mechanism to bypass a portion of the vapor in the compression mechanism to the discharge passage; a valve positioned near the port to control vapor flow through the port; the valve having a first position to permit a first vapor flow from the compression mechanism to the discharge passage, a second position to permit a second vapor flow from the compression mechanism to the discharge passage and a third position to prevent vapor flow from the compression mechanism to the discharge passage; the compressor having a first volume ratio in response to the valve being in the first position, a second volume ratio in response to the valve being in the second position and a third volume ratio in response to the valve being in the third position, the first volume ratio being less than the second volume ratio and the the second volume ratio being less than the third volume ratio; at least one solenoid valve, the at least one solenoid valve being positioned to control a flow of fluid to the valve, wherein the flow of fluid to the valve determines the position of the valve;, characterized by a controller, the controller comprising a microprocessor to execute a computer program to energize and de-energize the at least one solenoid valve to control the flow of fluid to the valve and adjust the position of the valve in response to an operating parameter anda first solenoid valve and a second solenoid valve, the first