Patent ID: 7171820

Claim:
A refrigerant cycle comprising: a compressor; a first heat exchanger downstream of said compressor; an expansion device downstream of said first heat exchanger; a second heat exchanger downstream of said expansion device; a refrigerant passing from said compressor, to said first heat exchanger, to said expansion device, to said second heat exchanger, and then back to said compressor, said refrigerant operating in a transcritical mode within said refrigerant cycle; and a control having an error correction algorithm for controlling an aspect of said refrigerant cycle to move said aspect to approach a desired value, said error correction algorithm looking at both a determined error between an actual value and said desired value, and the derivative of said determined error, and said control algorithm substituting an alternative error value, should a condition of both the determined error, and the derivative of said determined error indicate said cycle is moving into an inefficient mode.