ALTITUDE PRESSURE VARIATIONS
Note. 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 (Ft. Above Sea Level) | Absolute Pressure of Atmosphere (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) | Absolute Pressure of Atmosphere (psi) | (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 pressure gauges.
- Start engine and allow to warm up.
- Set system to "COOL" and blower to "HIGH".
- Open car doors and hood.
- Run engine at fast idle for 2-3 minutes.
AIR CONDITIONING SYSTEM PERFORMANCE CHECK TABLE. Scheme 15
Scheme 15: AIR CONDITIONING SYSTEM PERFORMANCE CHECK TABLE
Ambient Temperature/Pressure A/C Chart. Scheme 16
Scheme 16: Ambient Temperature/Pressure A/C Chart
Evaporator Temperature/Pressure A/C Chart. Scheme 17
Scheme 17: Evaporator Temperature/Pressure A/C Chart
| LOW SIDE GAUGE | HIGH SIDE GAUGE | 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. Cycling clutch systems only-Compressor doesn't turn on soon enough. | Defective Thermo- static Switch |
| Normal | Normal | Discharge air becomes warm as low side pressure rises. | Misadjusted Thermo- static 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 | Low High | Outlet air slightly cool. High side line cool to touch. Sweating or frost on high side. Evaporator outlet pipe cold. Low side goes into vacuum when blower is disconnected. | Restriction on High Side 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. |
AIR CONDITIONING DIAGNOSIS WITH GAUGES FOR SYSTEMS WITH INSUFFICIENT OR NO COOLING
