Refrigerant press filter in the direction of the flow arrow on the batch, by-pass overflow valve, if produced in excessive pressure drop through the element, the by-pass the overflow valve slightly open, in order to keep enough air and cools the closed compressor motor properly. When the suction filter installation direction is opposite to the direction of the arrow, by-pass overflow valve doesn't work, no matter how much pressure drop, it won't open it. At this moment need to pick up a repair valve, in order to measure the hair element to auxiliary compressor suction valve pressure drop. If the suction filter bypass relief valve doesn't work, can be used the repair valve for pressure measurement.