A/C Performance Testing

Fig. 3 A/C Preliminary Diagnosis Test:

Fig. 4 A/C Clutch Cycle Time Chart:

Fig. 5 Temperature-pressure Relationship Chart:

Pressure And Clutch Cycle Timing Evaluation:

Insufficient A/C Cooling:

CLUTCH CYCLE RATE
Diagnosis of the refrigerant system can be performed by analyzing the clutch cycle rate (time ON plus time OFF). The refrigerant system pressures, will vary between high and low points during the clutch cycle. Compare the system pressures, and clutch cycle rate, to the chart to determine if the system pressures and clutch cycle rate are normal.

NOTE: The conditional requirements given for the refrigerant system tests must be satisfied to obtain accurate pressure readings.

CLUTCH CYCLING SWITCH
The lowest pressure recorded on the low pressure gauge (observed when the clutch is disengaged) is the low pressure setting of the clutch cycling pressure switch.

NOTE: The low pressure (suction) cannot be measured with the cycling switch in place. This is because both the cycling switch and the connection for the low pressure line need to share the same valve.

MEASURING SYSTEM PRESSURE
To measure low pressure on the low pressure gauge, the cycling switch connector must be electrically jumped. This is done to simulate the cycling times as seen with the cycling switch in place. If the high pressure gauge exceeds the recommended pressures, the jumper must be removed from the cycling switch connector.

CAUTION: Failure to limit this high pressure could damage the A/C system.

The pressure recorded when the clutch engages is the high pressure setting of the pressure switch.

If the conditional requirements given in the chart are not satisfied, the pressure readings will not be accurate. This could indicate that a system or component that appears to be operating properly, is not operating properly. This can be used to determine what is causing the problem in the system. Compare the pressure results and the clutch cycle rate with the pressure conditions and clutch cycle time chart.

AFTER SERVICING
After servicing and correcting a refrigerant system problem, take additional pressure readings. Observe the clutch cycle rate while meeting the conditional requirements to be sure the problem has been corrected.

NOTE: In ambient temperatures above 32°C (90°F), the compressor clutch will not normally cycle off. This will depend on local conditions and engine/vehicle speed. Also, clutch cycling will normally not occur when the engine is operating at curb idle speed.If the system does not contain any refrigerant, or is extremely low on refrigerant, the clutch will not engage for compressor operation. A rapid cycling compressor clutch is usually an indication that the system is low on refrigerant.