Check Description

This test measures the operating efficiency of the A/C system under the following conditions:

• The Current Ambient Air Temperature
• The Current Relative Humidity
• The High Side Pressure Of The A/C System
• The Low Side Pressure Of The A/C System
• The Temperature Of The Air Being Discharged Into The Passenger Compartment

1. Park the vehicle inside or in the shade. Open the windows in order to ventilate the interior of the vehicle. If the A/C system was operating, allow the A/C system to equalize (about 2 minutes). Ensure that the ignition key is in the OFF position. Install the ACR 2000 Air Conditioning Service Center. Record the ambient air temperature displayed on the ACR 2000 Air Conditioning Service Center. Record readings of the low and high side static pressures. Are both the low and high side pressures within the specified value?
   • Above 60°F (16°C) - 50 Psi (345 kPa)
   • Above 75°F (24°C) - 70 Psi (483 kPa)
   • Above 90°F (33°C) - 100 Psi (690 kPa)
   If so, go to next step. If not, leak test system. See LEAK TESTING in GENERAL SERVICING PROCEDURES article in GENERAL SERVICING.
NOTE: Record the relative humidity and the ambient air temperature at the time of the test.
NOTE: When performing this step it is necessary to press the RESET button on the ACR 2000 Air Conditioning Service Center before pressing the PRINT button.
2. Close the vehicle doors and windows. Open the driver door window 5-6 inches (12.7-15.2 cm). Set the HVAC control to the following positions:
   • The A/C Is In Max Mode
   • The A/C On
   • The Coldest Temperature Setting
   • The Maximum Blower Speed
   • The I/P Panel Outlet Mode
   • All I/P Panel Outlets Are Open
   • The Passenger Side Of A Dual Zone HVAC Control Assembly Is Turned Off
   Install the temperature probes of the ACR 2000 Air Conditioning Service Center in the left and right center panel air outlets. Apply the parking brake. Place the transaxle in Park. Start the engine and allow to idle. Operate the A/C system for 5 minutes. Inspect A/C components for abnormal frost areas or unusual noises.

   Print the following information:

   • The Panel Outlet Air Temperatures
   • The Low-Side Pressure
   • The High-Side Pressure
   Compare the low and high side pressures and the panel output temperatures to the tables. See Fig 2 and Fig 1 . Does all the data recorded fall within the specified ranges of the tables? If so, go to step  4. If not, go to next step.

3. If the pressures and temperatures recorded do not fall within the specified ranges, continue to operate the A/C system for an additional 5 minutes. Record the pressures and temperatures again. Compare the low and high side pressures and the panel output temperature to the table below. Does all the data recorded fall within the specified ranges of the table below? If so, go to step  8. If not, go to next step.
4. Do the high and low side pressures fall within the specified ranges, but the panel outlet temperatures do not? If so, go to A/C PRESSURE ZONE "A" DIAGNOSIS  under SYSTEM TESTS. If not, go to next step.
5. Is the low side pressure greater than the specified range, but the high side pressure is within or less than the specified range? If so, go to A/C PRESSURE ZONE "B" DIAGNOSIS  under SYSTEM TESTS. If not, go to next step.
6. Are the low and high side pressures both greater than the specified ranges? If so, go to A/C PRESSURE ZONE "C" DIAGNOSIS  under SYSTEM TESTS. If not, go to next step.
7. Is the high side pressure greater than the specified range, but the low side pressure is within or less than the specified range? If so, go to A/C PRESSURE ZONE "D" DIAGNOSIS  under SYSTEM TESTS. If not, go to next step.
8. Operate the system in order to verify the test results. Did you find the same results? If so, system is okay. If not, go to SYMPTOM DIAGNOSIS  under TROUBLE SHOOTING.

Fig 1: A/C System Pressure/Zone Classification Chart

Courtesy of GENERAL MOTORS CORP.

Fig 2: A/C Performance Table

Courtesy of GENERAL MOTORS CORP.