CBCAUTO
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.
CBCAUTO
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.
CBCAUTO
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.
CBCAUTO
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
CBCAUTO
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.
CBCAUTO
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
CBCAUTO
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
CBCAUTO
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
CBCAUTO
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
CBCAUTO
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
CBCAUTO
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
CBCAUTO
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
CBCAUTO
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
CBCAUTO
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.
CBCAUTO
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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