Patent ID: 7784296

Claim:
A method for controlling an expansion valve of an air conditioning system having an evaporator configured to evaporate a refrigerant, the expansion valve having an open position, a closed position and a plurality of intermediary positions, the method comprising: calculating a superheat value of the refrigerant exiting the evaporator; determining whether the calculated superheat value matches a target superheat value; if the calculated superheat value matches the target superheat value, leaving the expansion valve at its current position; operating the expansion valve according to a first control procedure for adjusting the position of the expansion valve, the first control procedure implementing first and second Proportional, Integral, Derivative (PID) control algorithms where the first and second PID control algorithms are different from each other; determining whether the calculated superheat value is within a preset range of a target superheat value; if the calculated superheat value is outside of the preset range, operating the expansion valve in accordance with a third PID control algorithm to bring the calculated superheat within the preset range; and if the calculated superheat value is within the preset range, operating the expansion valve in accordance with a second control procedure for adjusting the position of the expansion valve to cause the calculated superheat to match the target superheat, wherein the first and second control procedures are different.