Chapter 25 Installation and Troubleshooting of Domestic Refrigerators and Freezers 661 Copyright Goodheart-Willcox Co., Inc. 8 the electrical system operates correctly, the compressor may not be pumping. The best check of the compressor is its volt-ampere (watt) reading at normal low-side and high-side pres- sures. If the volt-ampere reading is below the motor’s rating, the pump may be worn out. If the compressor is operating correctly but not building up pressure, check for internal problems with the compressor. To check the compressor’s pumping ability, install a piercing valve on the suc- tion line and attach a compound gauge. Pinch the suction line as shown in Figure 25-27. Next, run the Goodheart-Willcox Publisher Figure 25-26. To test a capacitor-start compressor, remove all electrical leads and then connect a test cord as shown. If the compressor operates properly when manually started, the problem is external. Common Fuse Ground Run Start C S R 1 2 3 4 Red Black Blue Green Compressor Start capacitor Pinched suction line Compressor Evaporator Condenser Capillary tube Gauge manifold Filter-drier High-pressure vapor Low-pressure vapor High-pressure liquid Low-pressure liquid Vacuum Goodheart-Willcox Publisher Figure 25-27. A compressor’s capacity can be tested by pinching the suction line and then running the compressor. The compressor must only be allowed to run for a very brief period of time, otherwise the motor will overheat. The compressor should pull 25 in. Hg to 28 in. Hg of vacuum within a few seconds. The yellow area indicates the vacuum in the line.