Patent ID: 7975497

Claim:
A refrigeration unit comprising: a refrigerant circuit formed by sequentially connecting a variable performance compressor, a condenser, a throttle valve and an evaporator, wherein a refrigerant is compressed by said compressor, cooled through said condenser and vaporized through said evaporator for performing a cooling action, and wherein performance of said compressor is variable by changing a rotational speed of said compressor; a sensor configured to measure a physical amount corresponding to a refrigerant pressure on a high-pressure side of said refrigerant circuit; a comparator configured to compare a measured value of the physical amount with a first reference value corresponding to a first predetermined pressure of the refrigerant, to compare the measured value of the physical amount with a second reference value corresponding to a second predetermined pressure lower than the first predetermined pressure, and to compare the measured value of the physical amount with a third reference value corresponding to a third predetermined pressure lower than the second predetermined pressure; and a compressor controller configured to control said compressor in at least four control operations: (i) a first control operation in which said compressor controller allows said compressor to maintain rotational speed and also prohibits said compressor from increasing rotational speed; (ii) a second control operation in which said compressor controller lowers rotational speed of said compressor to gradually lower performance of said compressor; (iii) a third control operation in which said compressor controller starts a protective operation of said refrigerant circuit; and (iv) a controlled refrigerating operation in which the rotational speed of said compressor can increase and decrease according to a desired performance of said refrigeration circuit; wherein said compressor controller is configured to control said compressor under the controller refrigerating operation when the measured value of the physical amount is lower than the third predetermined value based on a comparison result from said comparator, and wherein said compressor controller is configured to control said compressor under the first control operation when the measured value of the physical amount is between the third predetermined value and the second predetermined value based on a comparison result from said comparator, to control said compressor under the second control operation when the measured value of the physical amount is between the second predetermined value and the first predetermined value based on a comparison result from said comparator, and to control said compressor under the third control operation when the measured value of the physical amount is higher than the first predetermined value based on a comparison result from said comparator.