Chapter 25 Installation and Troubleshooting of Domestic Refrigerators and Freezers 659 Copyright Goodheart-Willcox Co., Inc. 8 Effect of Altitude on Refrigerator Temperatures A refrigeration system with a sensing bulb ther- mostat calibrated for use at sea level may run too cold at elevations above 5000′. This is a result of the decreased atmospheric pressure at higher elevations. Changes in altitude affect only pressure-sensitive ele- ments. Altitude does not affect bimetal and electronic thermostats. As altitude rises, atmospheric pressure drops. Beyond certain elevations, the reduced atmospheric pressure lowers the pressure on a pressure control’s diaphragm or bellows enough to affect the settings. The altitude adjustment and range control pressure for the bellows or diaphragm should be increased if the system will be operating at a high elevation. This adjustment compensates for the lower atmospheric pressure. To adjust for altitude, the cut-in and cut-out adjust- ment screws are turned the appropriate number of degrees. The location of the adjustment screws and the adjustment procedure varies from model to model. Always check the service manual of the equipment being serviced. Figure 25-25 shows one thermostat with an altitude adjustment and its altitude adjustment table. 25.4.2 Identifying Common Problems The following are common conditions that can develop inside a system and negatively affect its per- formance. Being familiar with these common prob- lems will help a technician effectively diagnose and repair a malfunctioning system. The presence of a restriction can be checked by looking at the high-side and low-side pressures. If a restriction is present at the metering device, the high- side pressure will be very high, and the low-side pres- sure will be very low. For example, an R-134a system that normally operates with a suction pressure of 5–10 psig and head pressure of 150 psig may have a vacuum on the low side and a head pressure over 200 psig. Tubing Ball bearing A B Inner tubing wall Original tubing shape 00 55 50 45 35 30 For altitude correction, both “cut-in” and “cut-out” screws must be adjusted Adjustment Altitude in Feet Co l d 2,000 3,000 4,000 5,000 6,000 7,000 8,000 9,000 10,000 This scale may be used as a guide for measuring degrees of rotation required for altitude correction. The arrows indicate direction of screw rotation. 7/60 13/60 19/60 25/60 31/60 37/60 43/60 49/60 55/60 Counterclockwise Turns 25 20 15 10 5 40 Goodheart-Willcox Publisher Figure 25-23. Ball bearing–type pinch-off tool. Amana Refrigeration, Inc. Figure 25-25. Thermostat equipped with an altitude adjustment. The table indicates the correct setting for various elevations. Goodheart-Willcox Publisher Figure 25-24. Pinch-off tool deformations. A—Flat deformation pinch-off seal. B—Half-circle deformation pinch- off seal.