# AIR CONDITIONING SYSTEM DIAGNOSIS

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AIR CONDITIONING SYSTEM DIAGNOSIS
CHAP 4 AND 7

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.

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.

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.

A C S Y S T E M Low side Expansion Valve High side

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

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.

NORMAL OPERATION Ambient Temperature: 90 degrees Fahrenheit
Low-side gauge: Normal pressure CFC-12: PSI HFC-134a: PSI High-side gauge: Normal pressure CFC-12: PSI HFC-134a: PSI

PLATE 1 Normal expansion valve system

PLATE 9 Normal orifice tube system

INSUFFICIENT COOLING #2
Low side Gauge: Low Pressure CFC psig HFC-134a 12 psig High Side Gauge: Normal Pressure CFC psig HFC-134a psig Possible Causes: Thermostat (icing) Low side restriction Moisture in system pg 70C

CONDITION #2

INSUFFICIENT OR NO COOLING #3
page 71C Low Side Gauge: Low or Very low Pressure CFC-12: psig HFC-134a : 15 psig High Side Gauge: Low Pressure CFC-12: psig HFC-134a: psig Possible causes: Clogged TXV inlet screen, bad valve, Moisture in system

INSUFFICIENT OR NO COOLING #4
Pg 72C INSUFFICIENT OR NO COOLING #4 Low side gauge: Low Pressure CFC-12: 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

INSUFFICIENT OR NO COOLING #5
Pg 73C INSUFFICIENT OR NO COOLING #5 Low side: High Pressure CFC-12: psig HFC-134a: 43 psig High side: Low Pressure CFC-12: psig HFC-134a: 150 psig Causes: Bad Clutch, Bad compressor (compressor not turning normally mech... or electrical)

INSUFFICIENT COOLING #6
pg 74C Low Side: High Pressure CFC-12: 40 psig HFC-1334a 38 psig High Side: Normal Pressure CFC-12: psig HFC-134a: psig Causes: Expansion Valve stuck open

INSUFFICIENT OR NO COOLING #7
Pg 75C INSUFFICIENT OR NO COOLING #7 Low Side: High Pressure CFC-12: psig HFC-134a: 37 psig High Side: High to extremely High CFC-12: psig HFC-134a: 263 psig Causes: Air in system, Overcharge, overcharge of oil, Clogged condenser, Non op Fans, Engine overheating

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

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.

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