GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2008 🢒 TopKick C-Series (Conventional) C4/C5 🢒 HVAC 🢒 Heating, Ventilation, and Air Conditioning 🢒 Air Conditioning (A/C) System Performance Test
Table 1: A/C Performance Table

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

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. This step determines if the A/C system has at least the minimum refrigerant charge required to operate the system without damage.

    2.

  2. This step measures the performance of the A/C system.

    3.

  3. This step is to allow for vehicle variations as well as high ambient temperatures.

Step

Action

Values

Yes

No

Important: 

   • The ambient air temperature must be at least 16°C (60°F) .
   • Do not induce additional air flow across the front of the vehicle during the test.
   • If you were sent here from a DTC diagnostic table, clear the DTC upon completion of this test.

1

  1. Park the vehicle inside or in the shade.
  2. Open the windows in order to ventilate the interior of the vehicle.
  3. If the A/C system was operating, allow the A/C system to equalize for about 2 minutes.
  4. Turn OFF the ignition.
  5. Install the J 39500-B .
  6. Record the ambient air temperature displayed on the J 39500-B .
  7. Record the low and high side STATIC pressure readings.

Are both the low side and high side pressures within the specified value?

More than 16°C (60°F) - 345 kPa (50 psi)

More than 24°C (75°F) - 483 kPa (70 psi)

More than 33°C (90°F) - 690 kPa (100 psi)

Go to Step 2

Go to Leak Testing

2

    Important: Record the relative humidity and the ambient air temperature at the time of the test.

  1. Close the vehicle doors and windows.
  2. Open the drivers door window 5-6 inches.
  3. Select the following HVAC control settings:
  4. A/C in recirculation mode
    5. • The A/C is ON
    • The maximum blower speed
    • The panel mode
    • The coldest temperature setting
    • All A/C outlets are OPEN
  5. Install the temperature probes of the J 39500-B in the left and right center A/C air outlets.
  6. Apply the parking brake.
  7. Place the transaxle/transmission in one of the following positions:
    8. • PARK (Automatic)
    • NEUTRAL (Manual)
  8. Start the engine.
  9. Operate the A/C system for 5 minutes.
  10. Inspect A/C components for the following conditions:
    11. • Abnormal frost areas
    • Unusual noises
  11. Record the following information:
    12. • The outlet air temperatures
    • The low-side pressure
    • The high-side pressure
  12. Compare the low and high side pressures and the output temperatures to the table below.

Does all the data recorded fall within the specified ranges of the table below?

--

Go to Step 8

Go to Step 3

3

If the pressures and temperatures recorded do not fall within the specified ranges:

  1. Continue to operate the A/C system for an additional 5 minutes.
  2. Record the pressures and temperatures again.
  3. Compare the low and high side pressures and the output temperature to the table below.

Does all the data recorded fall within the specified ranges of the table below?

--

Go to Step 8

Go to Step 4

4

Do the high and low side pressures fall within the specified ranges, but the outlet temperatures do not?

--

Go to Air Conditioning (A/C) Diagnostics - Pressure Zone A

Go to Step 5

5

Is the low side pressure greater than the specified range, but the high side pressure within or less than the specified range?

--

Go to Air Conditioning (A/C) Diagnostics - Pressure Zone B

Go to Step 6

6

Are the low and high side pressures both greater than the specified ranges?

--

Go to Air Conditioning (A/C) Diagnostics - Pressure Zone C

Go to Step 7

7

Is the high side pressure greater than the specified range, but the low side pressure is within or less than the specified range?

--

Go to Air Conditioning (A/C) Diagnostics - Pressure Zone D

Go to Step 8

8

Operate the system in order to verify the test results.

Did you find the same results?

--

System OK

Go to Symptoms - HVAC Systems - Manual

A/C System Pressure -- Zone Classification
Object Number: 799407 Size: MF

A/C Performance Table

Ambient Air Temperature

Relative Humidity

Service Port Pressure

Maximum Left Center Discharge Air Temperature

Low Side

High Side

13-18°C (55-65°F)

0-100%

259-358 kPa (38-52 psi)

1210-1590 kPa (176-231 psi)

4°C (39°F)

19-24°C (66-75°F)

Below 40%

280-391 kPa (41-57 psi)

1380-1780 kPa (200-258 psi)

5°C (42°F)

Above 40%

301-410 kPa (44-61 psi)

1440-1870 kPa (209-271 psi)

8°C (46°F)

25-29°C (77-84°F)

Below 35%

334-430 kPa (49-62 psi)

1650-1990 kPa (239-288 psi)

9°C (48°F)

35-60%

348-440 kPa (51-64 psi)

1690-2030 kPa (245-295 psi)

9°C (48°F)

Above 60%

358-462 kPa (52-67 psi)

1720-2100 kPa (250-305 psi)

10°C (50°F)

30-35°C (86-95°F)

Below 30%

375-476 kPa (54-69 psi)

1860-2240 kPa (270-325 psi)

11°C (52°F)

30-50%

386-491 kPa (56-71 psi)

1900-2300 kPa (276-334 psi)

15°C (60°F)

Above 50%

400-513 kPa (58-75 psi)

1950-2390 kPa (283-347 psi)

16°C (61°F)

36-41°C (97-106°F)

Below 20%

422-519 kPa (61-75 psi)

2100-2470 kPa (304-359 psi)

16°C (61°F)

20-40%

429-534 kPa (62-78 psi)

2130-2540 kPa (309-369 psi)

18°C (64°F)

Above 40%

444-549 kPa (64-80 psi)

2190-2600 kPa (317-377 psi)

18°C (64°F)

42-46°C (108-115°F)

Below 20%

472-561 kPa (69-81 psi)

2360-2680 kPa (343-389 psi)

20°C (68°F)

Above 20%

479-576 kPa (70-84 psi)

2390-2760 kPa (347-401 psi)

21°C (69°F)

47-49°C (117-120°F)

Below 30%

521-594 kPa (76-86 psi)

2600-2850 kPa (377-414 psi)

22°C (72°F)