Procedure

Poor air conditioning system performance can be caused by an obstructed A/C evaporator core. Airflow is restricted.

This condition can be detected by checking the center register discharge temperature. An abnormally low temperature indicates air is spending more time in the A/C evaporator core and is very cold when discharged, although the airflow volume is not enough to cool the vehicle properly.

Additional cause components are listed at the bottom of the System Evaluation Charts for poor compressor operation or a damaged compressor condition. System Evaluation Charts

The System Evaluation Charts provide the most direct and sure way to determine the cause of any problem in a poorly performing refrigerant system.

After servicing and correcting a refrigerant system concern, take additional pressure readings and observe the cycle rate while meeting the conditional requirements to be sure the concern has been corrected.

To diagnose a problem in the refrigerant system, note the system pressure (shown by the gauges) and the clutch cycle rate. Then compare readings with the Normal Cycle Rate/Temperature/Pressure Charts. Normal Cycle Rate/Temperature/Pressure Charts To achieve accurate results in the least amount of time, use the following procedure.

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

1. Connect a gauge set to the system.
2. When system has stabilized, record high and low pressures as shown by gauges.
3. Determine cycle rate per minute (ON time plus OFF time is one cycle).
4. Record OFF time in seconds.
5. Record ON time in seconds.
6. Note center register discharge temperature.
7. Determine and record ambient temperature.
8. Compare test readings and appropriate chart. System Pressure and Cycle Timing Evaluation Charts
a. Plot a vertical line for recorded ambient temperature from scale at bottom of each chart to top of chart.
b. Plot a horizontal line for other test readings from scale at left side of appropriate chart.

If the point where the two lines cross on each chart 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 problem and the specific cause must be determined. Refer to the System Evaluation Charts. System Evaluation Charts
1. System high (discharge) - pressure is high, low or normal.
2. System low (suction) - pressure is high, low or normal.
3. Cycle rate is fast, slow or A/C clutch runs continuously.
4. ON time is long or short.
5. OFF time is long or short.

Match these conditions to the conditions shown in the first five columns in the System Evaluation Charts. All five system conditions will be indicated on one line. The most likely component or components causing the problem are listed in the last column. System Evaluation Charts