SECTION 5 COMMERCIAL REFRIGERATION UNIT 29 TROUBLESHOOTING AND

SECTION 5 COMMERCIAL REFRIGERATION UNIT 29: TROUBLESHOOTING AND TYPICAL OPERATING CONDITIONS FOR COMMERCIAL REFRIGERATION

UNIT OBJECTIVES After studying this unit, the reader should be able to • List the typical operating temperatures and pressures for the low-pressure side of a refrigeration system for high, medium, and low temperatures. • List the typical operating pressures and temperatures for the high-pressure side of a system. • State how different refrigerants compare on the high-pressure and low-pressure sides of the system.

UNIT OBJECTIVES After studying this unit, the reader should be able to • Diagnose an inefficient evaporator. • Diagnose an inefficient condenser. • Diagnose an inefficient compressor.

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

STORAGE REQUIREMENTS FOR COMMON FOOD ITEMS Product Temperature Relative Humidity Storage Life Celery 31 to 32°F 90 to 95% 2 - 4 months Cucumbers 45 to 50°F 90 to 95% 10 – 14 days Butter 32 to 40°F 80 to 85% 2 months Ice Cream -15°F N/A 3 months Milk 33°F N/A 7 days Eggs 29 to 31°F 80 to 85% 6 – 9 months Oranges 32 to 34°F 85 to 90% 8 – 12 weeks

COIL-TO-AIR TEMPERATURE DIFFERENTIALS TO MAINTAIN DESIRED BOX HUMIDITY Temperature Range Desired Humidity Temperature Difference (Refrigerant to Air) 15°F or less 25 to 45°F 90% 8 to 12°F 25 to 45°F 85% 10 to 14°F 25 to 45°F 80% 12 to 16°F 25 to 45°F 75% 16 to 22°F 10°F and below -

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 25°F 45°F - 20°F = 25°F R-134 a at 25 degrees is 22 psig For R-134 a, a suction pressure below 22 psig is considered to be low

HIGH TEMPERATURE REFRIGERATION EVAPORATOR The evaporator coil is about 10°F to 20°F cooler than the box temperature BOX TEMPERATURE RANGES FROM 45°F to 60°F

HIGH TEMPERATURE REFRIGERATION EVAPORATOR The evaporator coil is about 10°F to 20°F cooler than the box temperature 25°F FOR A BOX TEMPERATURE OF 45°F, THE COIL WILL BE A TEMPERATURE OF ABOUT 25°F

HIGH TEMPERATURE REFRIGERATION EVAPORATOR The evaporator coil is about 10°F to 20°F cooler than the box temperature 25°F FOR R-134 a, THE PRESSURE AT 25°F WILL BE 22 PSIG 22 psig

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 10°F 30°F - 20°F = 10°F, R-134 a at 10°F is 11. 9 psig During the off cycle, the highest suction pressure will be 40 psig (R 134 a, 45°F box temperature) • After startup, the pressure will be about 22 psig (45 degrees – 20 degrees = 25 degrees)

MEDIUM TEMPERATURE REFRIGERATION EVAPORATOR 11. 9 psig 10°F BOX TEMPERATURE RANGES FROM 30°F to 45°F

MEDIUM TEMPERATURE REFRIGERATION EVAPORATOR 11. 9 psig 10°F FOR A BOX TEMPERATURE OF 30°F, THE COIL WILL BE A TEMPERATURE OF ABOUT 10°F

MEDIUM TEMPERATURE REFRIGERATION EVAPORATOR 11. 9 psig 10°F FOR R-134 a, THE PRESSURE AT 10°F WILL BE 11. 9 PSIG

Troubleshooting Low-Temp Applications • • • Low temperature applications start at 5°F Coil temperature is -15°F ( 5°F - 20°F = -15°F) For R-134 a, the highest suction is 0 psig at -15°F Lowest suction is 14. 7”Hg (-20°F - 20°F = -40°F) With the compressor off at 5°F, suction pressure for R-134 a is about 9. 1 psig • Use the P/T chart to determine pressures for other refrigerants

LOW TEMPERATURE REFRIGERATION EVAPORATOR The evaporator coil is about 10°F to 20°F cooler than the box temperature 14. 7 “Hg -15°F HIHGEST BOX TEMPERATURE IS 5°F

LOW TEMPERATURE REFRIGERATION EVAPORATOR The evaporator coil is about 10°F to 20°F cooler than the box temperature 14. 7 “Hg -15°F FOR A BOX TEMPERATURE OF 5°F, THE COIL WILL BE A TEMPERATURE OF ABOUT -15°F

LOW TEMPERATURE REFRIGERATION EVAPORATOR The evaporator coil is about 10°F to 20°F cooler than the box temperature -15°F FOR R-134 a, THE PRESSURE AT -15°F WILL BE 14. 7”Hg 14. 7 “Hg

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

90°F Outside Air Temp. High side pressure is 184. 6 psig + 30°F Temp. Differential 120°F Condensing Temp. R-134 a

90°F Outside Air Temp. High side pressure is 169 psig + 30°F Temp. Differential 120°F Condensing Temp. R-12

HIGH EFFICIENCY SYSTEM High side pressure is 124. 2 psig 90°F Outside Air Temp. + 10°F Temp. Differential 100°F Condensing Temp. R-134 a

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, 145°F sat. temp) – Leaving water is 95°F – Refrigerant is condensing at a temperature 50°F higher than the leaving water – Condenser is likely dirty (high temperature differential)

Compressor discharge 220 psig R-12 Condenser Liquid line to metering device For R-12, 220 psig = 145°F - 95°F = 50°F Condenser water in (90°F) Condenser water out (95°F) 50° IS TOO HIGH! CONDENSER TUBES MAY BE DIRTY!

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

SIX TYPICAL PROBLEMS • • • Low refrigerant charge Excess refrigerant charge Inefficient evaporator Inefficient condenser Restriction in the refrigerant circuit Inefficient compressor

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

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

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 20°F lower than the box temperature

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

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

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

COMPRESSOR VACUUM TEST • The compressor vacuum test is usually performed on a test bench with the compressor out of the system. • This test may be performed in the system when the system has service valves.

CLOSED-LOOP COMPRESSOR RUNNING BENCH TEST • Doing a running bench test on the compressor can be accomplished by connecting a line from the discharge to the suction of the compressor and operating the compressor in a closed loop. • Hermetic compressors should operate at close to full-load current in the closed loop when design pressures are duplicated.

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 30°F higher than ambient • Common system problems include overcharge, undercharge, restriction, inefficient compressor, condenser or evaporator