Refrigerant System Test

WARNING:
^ CARBON MONOXIDE IS COLORLESS, ODORLESS AND DANGEROUS. IF IT IS NECESSARY TO OPERATE THE ENGINE WITH THE VEHICLE IN A CLOSED AREA SUCH AS A GARAGE, ALWAYS USE AN EXHAUST COLLECTOR TO VENT THE EXHAUST GASES OUTSIDE OF THE CLOSED AREA.
^ R134A IS CLASSIFIED AS A SAFE REFRIGERANT, BUT MISUSE CAN MAKE IT DANGEROUS. THE FOLLOWING PRECAUTIONS MUST BE OBSERVED:
^ ALWAYS WEAR SAFETY GOGGLES WHEN SERVICING AN AIR CONDITIONING SYSTEM.
^ AVOID CONTACT WITH LIQUID REFRIGERANT R134A. R134A VAPORIZES AT APPROXIMATELY -20°F UNDER ATMOSPHERIC PRESSURE AND IT WILL FREEZE SKIN TISSUE.
^ NEVER ALLOW REFRIGERANT R134A GAS TO ESCAPE IN QUANTITY IN AN OCCUPIED SPACE. R134A IS NON-TOXIC, BUT IT WILL NOT FURNISH THE OXYGEN NEEDED TO SUPPORT LIFE.
^ NEVER USE A TORCH IN AN ATMOSPHERE CONTAINING R134A GAS. R134A IS NON-TOXIC AT ALL NORMAL CONDITIONS, BUT WHEN IT IS EXPOSED TO HIGH TEMPERATURES, SUCH AS A TORCH FLAME, IT DECOMPOSES. ONE OF THE PRODUCTS OF THE CHEMICAL BREAKDOWN IS A PHOSGENE GAS WHICH IS HIGHLY TOXIC.
^ CARE MUST BE EXERCISED SO AS NOT TO HEAT ANY PORTION OF THE CHARGED AIR CONDITIONING SYSTEM TOO HOT. THE PRESSURE IN AN AIR CONDITIONING SYSTEM RISES AS THE TEMPERATURE RISES AND TEMPERATURES OF APPROXIMATELY 200°F CAN BE DANGEROUS.

Poor air conditioning system performance can be caused by a plugged evaporator core or if the 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 evaporator core and is very cold when discharged, although the airflow volume is not enough to cool the vehicle properly.

Additional causes are listed at the bottom of the chart for poor compressor operation or a damaged compressor condition.

These 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 cycle rate while meeting the conditional requirements to be sure the problem has been corrected.

















To diagnose a concern in the refrigerant system, note the system pressure (shown by the gauges) and the clutch cycle rate, then compare readings with the charts.
^ The system pressures are low (compressor suction) and high (compressor discharge).
^ A cycle is the time the A/C clutch is engaged plus the time it is disengaged (time on plus time off).
^ Cycle times are the lengths of time (in seconds) that the A/C clutch is on or off.

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

To achieve accurate diagnosis results in the least amount of time, use the following procedure and refer to the Refrigerant System and Clutch Cycle Timing Evaluation Chart.

1. Connect a gauge set to the system.
2. When the system has stabilized, record high and low pressures as shown by the gauges.
3. Determine the cycle rate per minute (ON time plus OFF time equals one cycle).
4. Record the OFF time in seconds.
5. Record the ON time in seconds.
6. Note center register discharge temperature.
7. Determine and record the ambient temperature.
8. Compare the test readings on the appropriate chart.
a. Plot a vertical line for recorded ambient temperature from the scale at the bottom to the top of each chart.
b. Plot a horizontal line for other test readings from the scale at the left side of the appropriate chart.
c. If the point where the two lines cross on each chart falls within the heavy lines, the system is operating normally. If the lines cross outside the heavy lines on one or more of the charts, there is a problem and the specific cause must be determined. The following five system operating conditions are indicated where the lines cross the chart:
^ system high (discharge) - pressure is high, low, or normal
^ system low (suction) - pressure is high, low, or normal
^ cycle rate is fast, slow, or A/C clutch runs continuously
^ ON time is long or short
^ OFF time is long or short
9. Match these conditions to the conditions shown in the five columns toward the left in the Evaluation Chart. All five system conditions will be indicated on one line. The most likely component(s) causing the concern is indicated in the right column.