Refrigerant System Performance Check
NOTE: Test equipment must be connected to the refrigerant system to make system tests. If a charging station is used, follow the instructions of the station manufacturer.REFRIGERANT SYSTEM TESTS
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. Compare the findings to the charts:
^ The system pressures are low-side (A/C compressor suction) and high-side (A/C 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:
1. Run the engine at 1500 rpm for 10 minutes.
NOTE: When the ambient temperature exceeds 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 ), the 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.
2. Operate the A/C system on MAX A/C (recirculating air).
3. Run the blower motor at maximum speed.
4. Stabilize the in-vehicle temperature at 21° C to 27° C (70° F to 80° F).
NOTE: The test conditions, specified at the top of each chart, must be met to obtain accurate test results.
The following procedure is recommended for achieving accurate diagnosis results in the least amount of time:
^ Connect a manifold gauge set, Rotunda R-134a Manifold Gauge Set 176-R032A equivalent to the system.
^ Run the engine at 1500 rpm for 10 minutes.
^ Operate the A/C system on max A/C (recirculating air).
^ Run blower motor at max speed.
^ Stabilize the in-vehicle temperature at 21° C to 27° C (70° F to 80° F).
1. As soon as the system is stabilized, record the high-and low-pressures as shown by the 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).
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 temperatures.
7. Compare the test readings with the applicable previous charts.
a. Plot a vertical line for the recorded ambient temperature from the scale at the 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 Cycling Time 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 A/C compressor operation or a damaged A/C compressor condition.
8. The diagnosis charts provide the most direct and sure way to determine the cause of any concern in a poorly performing refrigerant system.
9. 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 in the previous charts to ensure the concern has been corrected.
10. 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 rpm/vehicle speed. Also. A/C clutch cycling will normally not occur when the engine is operating at curb idle speed.
NOTE: If the system contains no or very little refrigerant. the A/C clutch will not engage for A/C compressor operation. A rapid cycling AC clutch is usually an indication that the system is low on refrigerant.