1. AIR CONDITIONING SYSTEM DIAGNOSIS
CHAP 4 AND 7

2. 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.

3. 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.

4. 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.

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

6. 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

7. 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.

8. 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

9. PLATE 1
Normal expansion valve system

10. PLATE 9
Normal orifice tube system

11. 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

12. CONDITION #2

13. 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

14. 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

15. 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)

16. 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

17. 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

18. 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

19. 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.

20. 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

21. Your so Cool,
Later Babe!!!