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A/C Pressure Zone "A" Diagnosis

WARNING: Avoid contact with moving parts and hot surfaces while working around a running engine in order to prevent physical injury.
NOTE: Definition: The high and low side pressures may be normal or slightly less than normal.
  1. Were you sent here from the A/C PERFORMANCE TEST? If so, go to next step. If not, see A/C PERFORMANCE TEST  under PERFORMANCE TESTS.
  2. Refer to the air outlet temperatures recorded during the A/C system performance test. Is the difference in the discharge air temperature between the right and left center I/P outlets greater than 2-3 degrees? If so, go to step  7. If not, go to next step.
  3. Did the customer concern 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 2,000 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, go to A/C PRESSURE ZONE "D" DIAGNOSIS  under SYSTEM TESTS. 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 slightly above the specified pressure ranges but still within zone A on the A/C pressure-zone classification chart in the A/C PERFORMANCE TEST .
    • 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 slightly lower than the specified pressure ranges but still within zone A. See Figure.
    • 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, see TEST F: TOO HOT IN VEHICLE  in SYMPTOM TESTS.
  7. The A/C system may be undercharged. Leak test A/C system. See LEAK TESTING in GENERAL SERVICING PROCEDURES article in GENERAL SERVICING. After leak is repaired, recharge the A/C system to specifications. See RECOVERY, EVACUATING & RECHARGING in GENERAL SERVICING PROCEDURES article in GENERAL SERVICING. After repairs, go to step  14.
  8. The A/C system may be contaminated. View the ACR 2000 Refrigerant Station information screen 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. Recover the A/C system to a scavenging tank. See RECOVERY, EVACUATING & RECHARGING in GENERAL SERVICING PROCEDURES article in GENERAL SERVICING. Recharge the A/C system to specifications. After repairs, 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, EVACUATING & RECHARGING in GENERAL SERVICING PROCEDURES article in GENERAL SERVICING. Operate the A/C system and check the outlet air temperatures. See PERFORMANCE TESTS . Are the outlet temperatures within the specified ranges of the A/C PERFORMANCE TEST TABLE? See Figure. 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, EVACUATING & 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 the amount of refrigerant oil drained from the accumulator greater than 5 oz. (148 ml)? 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 in GENERAL SERVICING. Add the specified amount of refrigerant oil to the accumulator. See SPECIFICATIONS . Recharge the A/C system. See RECOVERY, EVACUATING & RECHARGING in GENERAL SERVICING PROCEDURES article in GENERAL SERVICING. After repairs are complete, go to step  15.
  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, EVACUATING & RECHARGING in GENERAL SERVICING PROCEDURES article in GENERAL SERVICING. After repairs are complete, go to step  15.
  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 CHART. See Figure. Are the high and low side pressures and outlet temperatures within specifications? If so, go to next step. If not, see A/C PERFORMANCE TEST  in 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 DIAGNOSIS  under TROUBLE SHOOTING.
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