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A/C Pressure Zone "A" Diagnosis

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WARNING: Avoid contact with moving parts and hot surfaces while working around a running engine in order to prevent physical injury.
NOTE: Tools Required: ACR 2000 Air Conditioning Service Center (J-43600).
  1. Were you sent here from the A/C System Performance Test? If so, go to next step. If not, go to A/C SYSTEM PERFORMANCE TEST  under PERFORMANCE TESTS.
  2. Refer to the panel air outlet temperatures recorded during the A/C system performance test. Does the discharge air temperature between the right and left center panel outlets vary by more than 2-3°F (1-2°C)? If so, go to step  7. If not, go to next step.
  3. Did the customer mention that the A/C system output temperatures are good at first, but then turn warm during extended drives? If so, go to next step. If not, go to step  5.
  4. Increase engine speed to 2000 RPM. During extended operation of the A/C system, does the low side pressure decrease, possibly accompanied by heavy frost on the liquid line between the orifice tube and the evaporator? If so, See A/C PRESSURE ZONE "D" DIAGNOSIS . If not, go to next step.
  5. Refer to the pressures recorded during the A/C system performance test. Inspect for the following conditions:
    • The high side pressure is slightly greater than the specified pressure ranges but still within Zone A on the A/C Pressure-Zone Classification Chart. See Fig 1 or Fig 2 .
    • The discharge line is hot.
    • The suction line is cool.
    Do the listed conditions exist? If so, go to step  7. If not, go to next step.
  6. Refer to the pressures recorded during the A/C system performance test. Inspect for the following conditions:
    • The low side pressure is slightly lower than the specified pressure ranges but still within Zone A on the A/C Pressure-Zone Classification Chart. See Fig 1 or Fig 2 .
    • The discharge line is warm-to-hot.
    • The suction line is cool-to-warm.
    Do the listed conditions exist? If so, go to next step. If not, go to TEST P: TOO HOT IN VEHICLE .
  7. The A/C system may be undercharged. Leak test A/C system. See LEAK TESTING in GENERAL SERVICING PROCEDURES article in GENERAL SERVICING. Recharge the A/C system to specifications. See RECOVERY, EVACUATION & RECHARGING in GENERAL SERVICING PROCEDURES article in GENERAL SERVICING. After repairs are complete, go to step  14.
  8. The A/C system may be contaminated. View the information screen on Air Conditioning Service Center for detection of foreign gases in the A/C system. Do foreign gases exist? If so, go to next step. If not, go to step  10.
  9. Evacuate the A/C system to a scavenging tank. See RECOVERY/EVACUATION & RECHARGING in GENERAL SERVICING PROCEDURES article in GENERAL SERVICING. Recharge the A/C system to specifications. After repairs are complete, go to step  14.
  10. The A/C system may contain too much moisture or air. Evacuate and recharge the A/C system to specifications. See RECOVERY/EVACUATION & RECHARGING in GENERAL SERVICING PROCEDURES article in GENERAL SERVICING. Operate the A/C system and inspect the panel outlet air temperatures. See A/C SYSTEM PERFORMANCE TEST  under PERFORMANCE TESTS. Are the panel outlet temperatures within the specified ranges of the A/C Performance Test Table? If so, go to step  15. If not, go to next step.
  11. The A/C system may contain too much refrigerant oil. Recover the refrigerant from the A/C system. See RECOVERY, EVACUATION & RECHARGING in GENERAL SERVICING PROCEDURES article in GENERAL SERVICING. Remove the accumulator. See ACCUMULATOR  under REMOVAL & INSTALLATION. Drain and measure the refrigerant oil from the accumulator. Was more than 5 oz. (148 ml) of refrigerant oil drained from the accumulator? If so, go to next step. If not, go to step  13.
  12. Reinstall the accumulator. See ACCUMULATOR  under REMOVAL & INSTALLATION. Flush the A/C system. See FLUSHING PROCEDURES in GENERAL SERVICING PROCEDURES in GENERAL SERVICING. Recharge the A/C system. See RECOVERY, EVACUATION & RECHARGING in GENERAL SERVICING PROCEDURES article in GENERAL SERVICING. After repairs are complete, go to step  14.
  13. Add the specified amount of refrigerant oil to the accumulator. See SPECIFICATIONS . Install the accumulator. See ACCUMULATOR  under REMOVAL & INSTALLATION. Recharge the A/C system. See RECOVERY, EVACUATION & RECHARGING in GENERAL SERVICING PROCEDURES article in GENERAL SERVICING. After repairs are complete, go to next step.
  14. Record the low and high side pressures and the I/P outlet air temperature. Compare the outlet temperatures to those listed in the A/C System Performance Table. See Fig 1 or Fig 2 . Are the high and low side pressures and I/P panel outlet temperatures within specifications? If so, go to next step. If not, go to A/C SYSTEM PERFORMANCE TEST  under PERFORMANCE TESTS.
  15. Operate the system in order to verify the repair. Did you find and correct the condition? If so, system is okay. If not, go to SYMPTOM TESTS .
Fig 1: A/C Zone Classification Chart
G00218165Courtesy of GENERAL MOTORS CORP.
Fig 2: A/C With Rear A/C Zone Classification Chart
G00218166Courtesy of GENERAL MOTORS CORP.
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