Refrigerant System Performance Check

Normal Fixed-Orifice Tube System Pressure Temperature/Relation:

Normal Clutch Cycle Rates And Times - For Fixed Orifice Systems:

The best way to diagnose a problem in the refrigerant system is to note the system pressures (shown by the manifold gauges), and the clutch cycle rate and times. Then, compare the findings to the charts shown.
^ The system pressures are low (compressor suction) and high (compressor discharge).
^ A clutch cycle is the time the clutch is engaged plus the time it is disengaged (time on plus time off).
^ Clutch cycle times are the lengths of time (in seconds) that the clutch is ON and OFF.

The following procedure is recommended for achieving accurate diagnosis results in the least amount of time.
1. Connect a manifold gauge set, part of Rotunda Air Conditioning Service Tool Kit 063-00010 or equivalent, to the system.

NOTE: The following test conditions must be met to obtain accurate test results:
^ Run engine at 1500 rpm for 10 minutes.
^ Operate A/C system on max A/C (recirculating air).
^ Run the blower at max speed.
^ Stabilize inside car temperature at 70° F to 80° F (21° C to 22° C).

2. As soon as the system is stabilized, record the high and low pressures as shown by the manifold gauges.
3. Determine the clutch cycle rate per minute (clutch on time plus off time is a cycle).
4. Record the clutch off time in seconds.
5. Record the clutch on time in seconds.
6. Record the center register discharge temperature.
7. Determine and record the ambient temperature.
8. Compare the test readings with the applicable 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.

A/C System And Clutch Cycle Rate Evaluation Chart W/Fixed Orifice Tube:

NOTE: If the point where the two lines cross on each of the charts falls within the shaded band, the system is operating normally. If the lines cross outside the shaded band on one or more of the charts, there is a problem and the specific cause must be determined. This is easily done by using the Refrigerant System and Clutch Cycle Timing Evaluation chart.

Refer to the following five operating conditions indicated by where the lines cross on the charts:
1. System high (discharge) pressure is high, low or normal.
2. System low (suction) pressure is high, low or normal.
3. Clutch cycle rate is fast, slow or the clutch runs continuously.
4. Clutch on time is long or short.
5. Clutch off time is long or short.
Match these conditions to the conditions shown in the five columns toward the left in the System Pressure and Clutch Cycle Timing Evaluation chart. All five system conditions will be indicated on one line. The most likely component or components causing the problem are listed in the column at the RH side of the chart.
Example: 1
^ High (discharge) pressure is low.
^ Low (suction) pressure is normal.
^ Clutch cycle rate is very fast.
^ Clutch on time is very short.
^ Clutch off time is very short.

NOTE: The component causing the problem is the clutch cycling pressure switch. The clutch cycling range is too close. Replace the switch and recheck the system.

Example: 2
^ High (discharge) pressure is normal to low.
^ Low (suction) pressure is normal.
^ Clutch cycle rate is fast.
^ Clutch on time is short.
^ Clutch off time is normal.

NOTE: The component causing the problem is the evaporator core. The airflow is restricted, indicating leaves or debris entering through the cowl air inlet are plugging the core.

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

At the bottom of the 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 problem in a poorly performing refrigerant system.

After servicing and correcting a refrigerant system problem, take additional pressure readings and observe the clutch cycle rate while meeting the conditional requirements to ensure 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.

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. Refer to Insufficient or No A/C Cooling-Fixed Orifice Tube Cycling Clutch System Diagnosis chart. Insufficient or No A/C Cooling-Fixed Orifice Tube System