Patent ID: 7380404

Claim:
A refrigerant system comprising: a compressor for compressing refrigerant and delivering refrigerant downstream to a condenser, refrigerant passing from said condenser to an expansion device, and from said expansion device to an evaporator, refrigerant from said evaporator passing back to said compressor; a control for controlling said refrigerant system, said control being provided with system variables from a plurality of sensors, and said control being operable to calculate mass flow rates by at least two methods based upon system variables, and said control being operable to compare the mass flow rate calculations by said two methods to each other, and indicate a low charge of refrigerant in said refrigerant system should said two mass flow rate calculations differ by more than a predetermined amount; and at least one of said two methods is calculated based upon a compressor model, and looking at a pressure ratio across said compressor.