Refrigerant System Performance

Climate Control System Refrigerant System Performance Evaluation

NOTE: Only equipment designed for R-134a refrigerant systems can be used for refrigerant system diagnosis. R-12 refrigerant service equipment should never be substituted or damage to the system or equipment may result.

The best way to diagnose a condition in the refrigerant system is to note the system pressures (shown by Rotunda R-134a Manifold Gauge Set 176-00032, or equivalent) and the A/C clutch cycle rate and times. Then, compare the findings to the charts.

^ The system pressures are low (compressor suction) and high (compressor discharge).
^ An A/C clutch cycle is the time the A/C clutch is engaged plus the time it is disengaged (time on plus time off).
^ A/C clutch cycle times are the lengths of time (in seconds) that the A/C clutch is on and off.

The following procedure is recommended for achieving accurate diagnosis results in the least amount of time:

1. Connect Rotunda R-134a Manifold Gauge Set 176-00032, or equivalent, to the system. Purge air from the red and blue hoses by loosening the fittings at the gauge set. Open only long enough for air to escape and then tighten the fittings.

NOTE: The test conditions, specified at the top of each chart, must be met to obtain accurate test results.

2. Start the engine and turn on the A/C system.

3. As soon as the system is stabilized, record the high- and low-pressures as shown by the manifold gauges. The low side should be between 240-344 kPa (35-50 psi). The high side should be between 1,226-1,618 kPa (178-235 psi). As low pressure drops, high pressure should rise. When the clutch disengages, the low side should rise and the high side should drop.
4. Determine the A/C clutch cycle rate per minute (A/C clutch on time plus off time is a cycle).
5. Record the A/C clutch OFF time in seconds.
6. Record the A/C clutch ON time in seconds.
7. Record the center duct temperature.
8. Determine and record the ambient temperature.









Refrigerant System Clutch Cycle Time and Rate Charts
The following test conditions must be established to obtain accurate A/C clutch cycle rate and cycle time readings:

^ Run the engine at 1500 rpm for 10 minutes.
^ Operate the A/C system on MAX A/C (recirculating air).

At the bottom of the refrigerant system pressure and A/C clutch cycle timing evaluation chart, additional cause components are listed for poor compressor operation or a damaged compressor condition.

The diagnosis charts provide the most direct and sure way to determine the cause of any concern in a poorly performing refrigerant system.

After servicing and correcting a refrigerant system concern, take additional pressure readings and observe the A/C clutch cycle rate while meeting the conditional requirements to ensure the concern has been corrected.

In ambient temperatures above 38°C (100°F), the A/C clutch will not normally cycle off and in many instances, the A/C clutch will not cycle off when temperatures are above 32°C (90°F). This will depend on local conditions and engine/vehicle speed. Also, A/C clutch cycling will normally not occur when the engine is operating at curb idle speed.

If the system contains no refrigerant or is extremely low on refrigerant, the A/C clutch will not engage for compressor operation. A rapid cycling A/C clutch is usually an indication that the system is low on refrigerant.