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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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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!!!