Refrigerant System Performance Check

DIAGNOSIS

Normal Fixed-Orifice Tube System Pressure Temperature Requirement:

A/C Clutch Cycle Rate:

Diagnosis of the refrigerant system can best be performed by analyzing the clutch cycle rate (time on plus time off) and the refrigerant system pressures, which will vary between high and low points during the clutch cycle. Compare the system pressures and clutch cycle rate to the charts shown to determine if the system pressures and clutch cycle rate are normal. The conditional requirements given in the charts for the refrigerant system tests must be satisfied to obtain accurate pressure readings.

The lowest pressure recorded on the low pressure gauge (observed when the clutch is disengaged) is the low pressure setting of the clutch cycle pressure switch. The pressure recorded when the clutch engages is the high pressure setting of the pressure switch.

Pressure And Clutch Cycle Timing Evaluation Chart W/Fixed Orifice Tube:

If the conditional requirements given in the charts are not satisfied, the pressure readings will not be accurate and could indicate that a system or component that appears to be operating properly is not. If the conditional requirements cannot be satisfied, the pressure readings will not be accurate but 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 shown in the third chart.

After servicing and correcting a refrigerant system problem, take additional pressure readings and observe the clutch cycle rate while meeting the conditional requirements in the first two charts, to be sure the problem has been corrected.

In ambient temperatures above 38° C (100° F), the compressor clutch will not normally cycle OFF, and in many instances, the clutch will not cycle OFF when temperatures are above 32° C (90°F). 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.

Insufficient A/C Cooling-Add A Partial Charge:

If the system contains no 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. Add a partial charge if a low refrigerant charge condition exists.