DESCRIPTION
Diagnosis is an important first step in A/C system servicing. To save time and effort, systems should be carefully checked to identify the causes of poor performance. By using the following diagnostic charts, defective components or system damage can be quickly located. To identify problems that are specific to one system, refer to the repair section of this manual. The charts in this section apply to all systems.
ALTITUDE PRESSURE VARIATIONS
| Altitude (Ft. Above Sea Level) | Absolute Atmospheric Pressure (psi) | (1) Gauge Altitude Correction (psi) |
|---|
| 0 | 14.7 | 0 |
| 1000 | 14.2 | 0.5 |
| 2000 | 13.7 | 1.0 |
| 3000 | 13.2 | 1.5 |
| 4000 | 12.7 | 2.0 |
| 5000 | 12.2 | 2.5 |
| 6000 | 11.7 | 3.0 |
| 7000 | 11.3 | 3.4 |
| 8000 | 10.9 | 3.8 |
| 9000 | 10.5 | 4.2 |
| 10,000 | 10.1 | 4.6 |
| (1) Subtract correction shown from gauge readings. |
| (1) | Subtract correction shown from gauge readings. |
ALTITUDE PRESSURE VARIATIONS
ALTITUDE VACUUM VARIATIONS
| Altitude (Ft. Above Sea Level) | Complete Vacuum (In. Hg) | (1) Gauge Altitude Correction (psi) |
|---|
| 0 | 29.92 | 0 |
| 1000 | 28.92 | +1.0 |
| 2000 | 27.82 | +2.1 |
| 3000 | 26.82 | +3.1 |
| 4000 | 25.82 | +4.1 |
| 5000 | 24.92 | +5.0 |
| 6000 | 23.92 | +6.0 |
| 7000 | 23.02 | +6.9 |
| 8000 | 22.22 | +7.7 |
| 9000 | 21.32 | +8.6 |
| 10,000 | 20.52 | +9.4 |
| (1) Add correction shown to gauge readings. |
| (1) | Add correction shown to gauge readings. |
ALTITUDE VACUUM VARIATIONS
PREPARATION FOR TESTING
- Attach Low and High side gauges.
- Start engine and allow it to warm up.
- Set system to COOL and blower to HIGH.
- Open car doors and hood.
- Run at fast idle for 2-3 minutes.
| Application | Low Side Guage (Suction) | High Side Guage (Discharge) |
|---|
| 1980-81 (Accumulator Type) | 24-35 | 150-220 |
| 1982-88 (Accumulator Type) |
| Front Wheel Drive | 22-29 | 165-205 |
| Rear Wheel Drive | 24-30 | 130-190 |
| (1) Normal System Operating Pressures (PSI) (2) Pressure readings given are for a system in good operating condition, at sea level and an ambient temperature of 80°F (27°C). |
| (1) | Normal System Operating Pressures (PSI) |
| (2) | Pressure readings given are for a system in good operating condition, at sea level and an ambient temperature of 80°F (27°C). |
OPERATIONAL TEST GAUGE READINGS (1) (2)
| Perform Temperature Test | Should Be | Check |
|---|
| Switch to LOW blower Close doors, Check outlet temperature | 35-45°F (1.7-7.2°C) | Too warm - Check control lever operation, heater water valve, cooling system and gauge readings |
AIR CONDITIONING SYSTEM PERFORMANCE CHECK - TEMPERATURE CHECK
| Perform Visual Check | Should Be | Check |
|---|
| Compressor | Quiet, no leaks | Noisy-Check belts, oil level, seals, gaskets, reed valves. |
| Condenser | Free of obstructions | Blocked-Clean off. Plugged. Flush or replace. |
| Receiver-Drier | Dry and warm to touch | Frosty-Check for restriction, replace desiccant. |
| Sight Glass | Clear or few bubbles | Bubbly, foamy or streaks. Check gauge readings. |
| High Side | Dry and warm to touch. | Frosty or very hot. Check for restriction or overcharge. |
| Low Side Lines | Dry and cool to touch. | Frosty or warm. Check for restriction, low charge or bad valve. |
| Expansion Valve | Dry | Frosty. Check for moisture or restriction. Check sensing bulb. |
| STV | Dry and cool to touch. | Frosty or warm. Check guage readings for valve malfunction. |
| Evaporator | Dry and cold to touch. | Freezing or warm. Check expansion valve, STV or thermo switch. |
AIR CONDITIONING SYSTEM PERFORMANCE CHECK - VISUAL CHECK
| Guage Readings Test | Should Be | Check |
|---|
| High Side Gauge | See Pressure Chart | Above or below normal. See A/C Diagnosis table. |
| Low Side Gauge | See Pressure Chart | Above or below normal. See A/C Diagnosis table. |
AIR CONDITIONING SYSTEM PERFORMANCE CHECK - VISUAL CHECK
AMBIENT TEMPERATURE/PRESSURE. Scheme 1
Scheme 1: AMBIENT TEMPERATURE/PRESSURE
EVAPORATOR TEMPERATURE/PRESSURE. Scheme 2
Scheme 2: EVAPORATOR TEMPERATURE/PRESSURE
| Low Side | High Side | Other Symptoms (1) | DIAGNOSIS |
|---|
| Normal | Normal | No or few bubbles in sight glass. High side gauge may go high. Low side gauge does not fluctuate with compressor on/off cycle. | Some Air and Moisture in System |
| Normal | Normal | Cools okay in morning but not during hot part of Day. Tiny bubbles in sight Glass. Discharge air warm when low side gauge drops into vacuum. | Excessive Moisture |
| Normal | Normal | Thermostatic switch system only compressor cycles off and on too rapidly. | Defective Thermostatic Switch |
| Normal | Normal | Cycling clutch systems only--Compressor doesn't turn on soon enough. Discharge air becomes warm as low side pressure rises. | Misadjusted Thermostatic Switch or Defective Pressure Sensing Switch |
| Low | Low | Bubbles in sight glass. Outlet air slightly cool. | Low R-12 Charge |
| Low | Low | Sight glass clear or oil- streaked. Outlet air very warm. | Excessively Low R-12 Charge |
| Low | Low | Outlet air slightly cool. Sweating or frost at at expansion valve. | Expansion Valve Stuck Closed. Screen Plugged or Sensing Bulb Malfunction. |
| Low | Low | Bubbles in sight glass. Outlet air slightly cool. | Low R-12 Charge |
| Low | Low | Sight glass clear or oil- streaked. Outlet air very warm. | Excessively Low R-12 Charge |
| Low | Low | Outlet air slightly cool. Sweating or frost at expansion valve. | Expansion Valve Stuck Closed. Screen Plugged or Sensing Bulb Malfunction. |
| Low | Low | Outlet air slightly cool. High side line cool to touch. Sweating or frost on high side. | Restriction on High Side |
| Low | High | Evaporator outlet pipe cold. Low side goes into vacuum when blower is disconnected. | STV Stuck Open |
| High | Low | Evaporator outlet pipe warm. Outlet air warm. | STV Stuck Open |
| High | Low | Noise from compressor. | Compressor Malfunction |
| High | High | Outlet air warm. Liquid line very hot. Bubbles in sight glass. | Condenser Malfunction or R-12 Overcharge. |
| High | High | Outlet air slightly cool. Bubbles in sight glass. | Large Amount of Air and Moisture in System. |
| High | High | Outlet air warm. Evaporator outlet sweating and frost. | Expansion Valve Stuck Open |
| (1) If equipped with a low refrigerant charge protection system, compressor operation may have stopped. |
| (1) | If equipped with a low refrigerant charge protection system, compressor operation may have stopped. |
A/C DIAGNOSIS W/GAUGES FOR SYSTEMS W/INSUFFICIENT OR NO COOLING
