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. Organized Troubleshooting. Have knowledge of how the system should operateKnow the product being refrigeratedMeasure pressures, temperatures, amperages and voltagesInspect the system for obvious problemsDefective components can trigger other problemsIt is rare for more than one component to f

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2. UNIT OBJECTIVES After studying this unit, the reader should be able to

3. Organized Troubleshooting Have knowledge of how the system should operate Know the product being refrigerated Measure pressures, temperatures, amperages and voltages Inspect the system for obvious problems Defective components can trigger other problems It is rare for more than one component to fail at any given time

6. Troubleshooting High-Temp Applications Boxes range from 45 to 60 degrees Coils are 10 to 20 degrees cooler than the box At the lowest temperature, the coil will be 25F 45F - 20F = 25F R-134a at 25 degrees is 22 psig For R-134a, a suction pressure below 22 psig is considered to be low

10. Troubleshooting Medium-Temp Applications Boxes range from 30 to 45 degrees Coils are 10 to 20 degrees cooler than the box At the lowest temperature, the coil will be 10F 30F - 20F = 10F, R-134a at 10F is 11.9 psig During the off cycle, the highest suction pressure will be 40 psig (R-134a, 45F box temperature) After startup, the pressure will be about 22 psig (45 degrees 20 degrees = 25 degrees)

14. Troubleshooting Low-Temp Applications Low temperature applications start at 5F Coil temperature is -15F ( 5F - 20F = -15F) For R-134a, the highest suction is 0 psig at -15F Lowest suction is 14.7Hg (-20F - 20F = -40F) With the compressor off at 5F, suction pressure for R-134a is about 9.1 psig Use the P/T chart to determine pressures for other refrigerants

18. Typical Air-Cooled Condenser Operating Conditions Head pressure controls maintain the desired head pressure, which is about 105F Most condensers operate with condensing temperatures about 30F higher than ambient High efficiency condensers can operate with condensing temperatures as low as 10F above ambient temperature

22. Typical Water-Cooled Condenser Operating Conditions Wastewater systems require about 1.5 gpm/ton Recirculating systems require about 3.0 gpm/ton Water-regulating valves maintain desired pressure R-12 system (head pressure of 220 psig, 145F sat. temp) Leaving water is 95F Refrigerant is condensing at a temperature 50F higher than the leaving water Condenser is likely dirty (high temperature differential)

24. Typical Conditions for Recirculating Water Systems Usually do not use water regulating valves Water enters at 85F and leaves at 95F Refrigerant normally condenses at a temperature that is 10F higher than the leaving water temp. Refrigerant normally condenses at about 105F Cooling tower water can often be cooled to a temperature within 7F of the wet bulb temperature of the ambient air

25. 6 Common System Problems Low refrigerant charge Excess refrigerant charge Inefficient evaporator Inefficient condenser Restriction in the refrigerant circuit Inefficient compressor

26. Symptoms of a Low Refrigerant Charge Reduced system capacity Low head pressure Low suction pressure (except for AXV systems) High superheat (Except for TXV systems) Sight glass will have bubbles in it Compressor will often run hot Suction line will be warm

27. Inefficient Evaporator System suction pressure will be low Evaporator does not absorb heat properly Caused by dirty or blocked coil, defective evaporator fan motor, defective expansion valve, or recirculating air Evaporator saturation temperature should be no more than 20F lower than the box temperature

28. Symptoms of a Refrigerant Overcharge High operating pressures (Except AXV systems) Capillary tube systems may have liquid floodback Low superheat (Except for TXV systems) High condenser subcooling Sweating is a sign that liquid may be entering the compressor

29. Inefficient Condenser High head pressure Refrigerant cannot desuperheat, condense and subcool refrigerant effectively Amount of cooling medium (air or water) must be sufficient Condenser discharge air must not be permitted to recirculate through the coil

30. Refrigerant Flow Restrictions Restrictions can be partial or full A pressure drop is created at the restriction Damaged or kinked tubing can cause a restriction A temperature difference will exist across a liquid line restriction Freezing moisture in the system can cause a restriction Improperly set valves or controls can be at fault

31. Inefficient Compressor Electrical problems are relatively easy to diagnose Evaluating pumping problems are more difficult Various tests can be performed on the compressor Compressor Vacuum Test Closed-Loop Compressor Running Bench Test Closed-Loop Compressor Running Field Test Compressor Running Test in the System

32. UNIT SUMMARY When troubleshooting, be organized! Evaporator coils are typically 10 to 20 degrees cooler than the box temperature Use the P/T chart to obtain operating temperatures Head pressure controls maintain desired pressures Standard efficiency condensers operate at temperatures that are about 30F higher than ambient Common system problems include overcharge, undercharge, restriction, inefficient compressor, condenser or evaporator

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