the pressurized refrigerant passing through the recovery valve block 412 next the rate of pressure increase is compared with an upper threshold block 416 if there is liquid refrigerant in the accumulator then the pressure rise in the accumulator will be greater than if there is only vapor refrigerant in the accumulator as such if the rate of the pressure increase in the accumulator when the valve is open is greater than a predetermined upper threshold the target pressure in the accumulator is decreased block 420 and the process advances to operation of the recovery valve using the adjusted target pressure at block 308 in some embodiments the predetermined upper threshold is the pressure increase rate at which there is known to be liquid in the accumulator while in other embodiments the upper threshold is selected as a value that is less than the rate at which there is known to be liquid in the accumulator in order to provide a safety factor to account for possible measurement errors if the rate of pressure increase is less than the predetermined upper threshold then the process continues by comparing the rate of pressure increase with a lower threshold block 424 the lower threshold is below the known value at which the refrigerant is entirely in the vapor state and is based on the rate of pressure increase resulting from a desired minimum efficiency for the recovery operation if the rate of pressure increase when the recovery valve is open is below the lower threshold then the target pressure in the accumulator is increased to improve recovery efficiency block 428 and the process advances to.