cbc auto air conditioning system diagnosis chap 4 and 7
TRANSCRIPT
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CBCAUTO
AIR CONDITIONING SYSTEM DIAGNOSIS
CHAP 4 AND 7
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OBJECTIVES
Diagnose six system malfunctions by gauge readings.
Identify the low and high side of the air conditioning system.
Read and understand temperature-pressure charts.
Discuss temperature-pressure relationships.
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OBJECTIVES Identify differences between
CFC-12 and HFC-134a systems. Identify differences between
thermostatic expansion valve (TXV) and fixed orifice tube (FOT) systems.
Understand the proper handling of refrigerants and refrigeration oil.
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INTRODUCTION Figure 4-1, (Pg 68C) shows the
dividing line between low and high sides.
Low side gauge is a compound gauge.
There is a direct relationship between pressure and temperature.
Air temp flowing through evaporator will be a few degrees warmer than the refrigerant.
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CBCAUTO
AC
SYSTEM
Low side
High side
Expansion Valve
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CHECK THESE FIRST BELT TENSION CLUTCH OPERATION RADIATOR/CONDENSER FAN OPERATION PROPER FLOW FROM DUCTS SIGHT GLASS IN R-12 SYSTEMS REFRIGERANT CHARGE SUCTION LINE LIQUID LINE SERVICE VALVES LINES, HOSES, CONNECTIONS
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SYSTEM DIAGNOSIS Knowing the ambient air
temperature. Determine normal HIGH side
pressure. (Pressure chart page 69C)
There are seven conditions for A/C systems.
1 normal condition. 6 conditions that indicate a malfunction.
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NORMAL OPERATIONAmbient Temperature: 90 degrees Fahrenheit
Low-side gauge: Normal pressure– CFC-12: 32-33 PSI– HFC-134a: 30-31 PSI
High-side gauge: Normal pressure– CFC-12: 185-190 PSI– HFC-134a: 204-210 PSI
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PLATE 1 Normal
expansion valve system
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PLATE 9 Normal
orifice tube system
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INSUFFICIENT COOLING #2
Low side Gauge: Low PressureCFC-12 15 psig
HFC-134a 12 psig
High Side Gauge: Normal Pressure CFC-12 190 psig HFC-134a 208 psig
Possible Causes: Thermostat (icing) Low side restrictionMoisture in system
pg 70C
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CONDITION #2
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INSUFFICIENT OR NO COOLING #3
Low Side Gauge: Low or Very low Pressure– CFC-12: 18 psig– HFC-134a : 15 psig
High Side Gauge: Low Pressure– CFC-12: 130-135 psig– HFC-134a: 139-144 psig
Possible causes: Clogged TXV inlet screen, bad valve, Moisture in system
page 71C
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INSUFFICIENT OR NO COOLING #4
Low side gauge: Low Pressure– CFC-12: 22 psig– HFC-134a: 20 psig
High side gauge: High to extremely High – CFC-12: 250 psig– HFC-134a 281 psig
Causes: Restriction in High Side– Temperature change present at
restriction
Pg 72C
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INSUFFICIENT OR NO COOLING #5
Low side: High Pressure– CFC-12: 44 psig– HFC-134a: 43 psig
High side: Low Pressure– CFC-12: 140 psig– HFC-134a: 150 psig
Causes: Bad Clutch, Bad compressor– (compressor not turning normally
mech... or electrical)
Pg 73C
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INSUFFICIENT COOLING #6
Low Side: High Pressure– CFC-12: 40 psig– HFC-1334a 38 psig
High Side: Normal Pressure– CFC-12: 170 psig– HFC-134a: 184 psig
Causes: Expansion Valve stuck open
pg 74C
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INSUFFICIENT OR NO COOLING #7
Low Side: High Pressure– CFC-12: 42 psig– HFC-134a: 37 psig
High Side: High to extremely High– CFC-12: 235 psig– HFC-134a: 263 psig
Causes: Air in system, Overcharge, overcharge of oil, Clogged condenser, Non op Fans, Engine overheating
Pg 75C
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R-22 for LEAK TESTING R-12 = 50psi R-22 = 100psi Do NOT mix refrigerants R-22 is NOT a replacement for
R-12 Small amounts of R-22 used in
leak testing can be vented to atmosphere.
Can Dye Test if needed (pg 197L)
page 82C
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SERVICING TIPS A/C oil level should be checked
each time the system is drained.
Keep the cap on oil container. Refrigerant oil is hygroscopic. Moisture is damaging to A/C
system. Add oil removed from system if
a major loss has occurred.
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PREVENTIVE MAINTENANCE
Inspect electrical system for A/C
Inspect Blower motor for abnormal noises, leaves in ducts, etc.
Check Voltages Check Compressor Clutch
operation Check Belts and A/C Hoses A/C Function Check
page 88
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Your so Cool, Later Babe!!!