Refrigerant System Performance Check

REFRIGERANT SYSTEM TESTS

A/C Clutch Refrigerant System Normal Pressure/Temperature Relationships:

Normal A/C Clutch Cycle Rates And Times:

The best way to diagnose a concern in the refrigerant system is to note the system pressures (shown by the manifold gauges) and the A/C clutch cycle rate and times. Then compare the findings to the charts:

NOTE: Test equipment must be connected to the refrigerant system to make the system tests. If a charging station is used, follow the instructions of the station manufacturer.

^ The system pressures are low-side (compressor suction) and high-side (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 test conditions must be established to obtain accurate pressure readings:
^ Run the engine at 1500 rpm for 10 minutes.

NOTE: When the ambient temperatures exceed 38° C (100 ° F), the engine should be run at normal idle speed only. For tests in ambient temperatures between 38° C and 43° C (100° F and 110° F), system performance pressures will be the same as those for ambient temperatures shown on the chart in the 32° C to 38° C (90° F to 100° F) range. The center A/C register discharge temperatures will also be similar to those shown in the chart in the 32° C to 38 ° C (90° F to 100° F) range.

^ Operate the A/C system on max A/C (recirculating air).
^ Run the blower motor at max speed.
^ Stabilize the in-vehicle temperature at 21° C to 27° C (70° F to 80° F).

The following procedure is recommended for achieving accurate diagnosis results in the least amount of time.
^ Connect a Rotunda R-134a Manifold Gauge Set 176-R032A or equivalent to the system.
^ Run the engine at 1500 rpm for 10 minutes.
^ Operate the A/C system on maximum A/C (recirculating air).
^ Run the blower motor at maximum speed.
^ Stabilize the in-vehicle temperature at 21° C to 27° C (70° F to 80° F).
1. As soon as system is stabilized, record the high and low pressures as shown by manifold gauges. Normally the suction pressure should decrease to a range between 152-193 kPa (22-28 psi) and the A/C cycling switch should open. When the A/C cycling switch opens, the suction pressure should start to rise to a range between 276-324 kPa (40-47 psi). Somewhere between 276-324 kPa (40-47 psi), the A/C cycling switch should close and the suction pressure should start to drop.

NOTE: The discharge (high) pressure should operate the reverse of the suction pressure. When the suction pressure is dropping, the discharge pressure should increase. When the suction pressure is increasing, the discharge pressure should decrease.

2. Determine the A/C clutch cycle rate per minute (A/C clutch ON time plus OFF time is a cycle).

NOTE: When the ambient temperature is above 27° C (80° F), the A/C clutch may not cycle.

3. Record the A/C clutch OFF time in seconds.
4. Record the A/C clutch ON time in seconds.
5. Record the center A/C register discharge temperature.
6. Determine and record the ambient temperature.
7. Compare the test readings with the applicable chart.
a. Plot a vertical line for the recorded ambient temperature from the scale at bottom of each chart to the top of each chart.
b. Plot a horizontal line for each of the other test readings from the scale at the LH side of the appropriate chart.

Refrigerant System Pressure And A/C Clutch Cycle Timing Evaluation Chart:

c. If the point where the two lines cross on each of the charts falls within the dark band, the system is operating normally. If the lines cross outside the dark band on one or more of the charts, there is a concern and the specific cause must be determined. This is easily done by using the Refrigerant System Pressure and A/C Clutch Cycle Timing Evaluation Chart.
d. At the bottom of the chart, additional cause components are listed for poor operation or a damaged A/C compressor condition.
e. The diagnosis charts provide the most direct and sure way to determine the cause of any concern in a poorly performing refrigerant system.
f. 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 make sure the concern has been corrected.
g. In ambient temperatures above 27° C (80° F), the A/C clutch will not normally cycle off. This will depend on local conditions and engine/vehicle speed. Also, cycling of the A/C clutch will normally not occur when the engine is operating at curb idle speed.
h. If the system contains no refrigerant or is extremely low on refrigerant, the A/C clutch will not engage for A/C compressor operation. A rapid cycling A/C clutch is usually an indication that the system is low on refrigerant.