GM Service Manual Online
For 1990-2009 cars only
Table 1: Insufficient Cooling Diagnosis
Table 2: A/C Performance Table

Test Description

The following test measures the A/C system operating efficiency by comparing:

    • The ambient air temperature at the time of the test
    • The ambient air humidity at the time of the test
    • The pressure at the high-pressure side of the refrigeration system
    • The pressure at the low-pressure side of the refrigeration system
    • The temperature of the air being discharged from the LH and RH center IP outlets into the passenger compartment

The number(s) below refer to the step number(s) on the diagnostic table.

  1. This step determines if there is enough refrigerant in the A/C system to operate it without damage.

  2. This step is to determine if the A/C compressor is operating.

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

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

Insufficient Cooling Diagnosis

Step

Action

Value(s)

Yes

No

1

Did you perform a Diagnostic System Check?

--

Go to Step 2

Go to A Diagnostic System Check in HVAC Systems - Manual or A Diagnostic System Check in HVAC Systems - Automatic

2

  1. Park the vehicle inside or in the shade. The ambient temperature must be at least 16°C (60°F).
  2. Open the windows and the doors in order to ventilate the interior of the vehicle.
  3. If the engine is at operating temperature, allow the engine to cool.
  4. Ensure that the ignition key is in the OFF position.
  5. Remove the left diagonal brace. Refer to Front End Sheet Metal Diagonal Brace Replacement in Body Front End.
  6. Connect the J 39500-B .
  7. Record readings of the low and high side STATIC pressures.
  8. The low and high side pressure readings should be almost equal to each other once the system has come to rest.

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

345 kPa (50 psi)

Go to Step 3

Go to Leak Testing

3

  1. Start the engine.
  2. Vent the engine exhaust.
  3. Turn the A/C ON.
  4. Visually inspect under the hood to see if the A/C compressor clutch is engaged.

Does the compressor clutch engage ?

--

Go to Step 4

Go to PCM Controlled A/C Circuit Diagnosis in Engine Controls - 3.5L

4

  1. Turn the engine OFF.
  2. Important: Record the relative humidity and the ambient temperature AT THE TIME OF THE TEST.

  3. Record the ambient temperature at the vehicle.
  4. Record the relative humidity, using one of the following methods:
  5. • Use a psychrometer.
    • Consult the local weather bureau.
  6. Open all of the vehicle doors and the windows.
  7. Set the HVAC control assembly to the following positions:
  8. • To recirculation (RECIR)
    • The blower control (speed) to the highest position
    • The HVAC control assembly to discharge air through the IP outlets
    • The temperature control(s) to the coldest position(s)
    • Turn the A/C ON.
  9. Open the IP air outlet deflectors
  10. Place a thermometer in the IP left center air outlet.
  11. Place a thermometer in the IP right center air outlet.
  12. Place the transaxle in PARK.
  13. Start the engine.
  14. Elevate the engine to 2000 RPM and maintain that RPM.
  15. Operate the A/C system until the outlet temperature reaches the lowest temperature (approximately 5 minutes).
  16. Record the following information:
  17. • The IP outlet air temperatures
    • The low-side pressure
    • The high-side pressure
  18. Turn the engine OFF. Compare the low and high side pressures and the IP output temperatures to the A/C Performance table below.

Does all the recorded data fall within the specified ranges of the A/C Performance table below?

--

Go to Step 10

Go to Step 5

5

If the pressures and temperatures recorded DO NOT fall within the specified ranges, perform the following steps:

  1. Start the engine and continue to operate the A/C system for an additional 5 minutes.
  2. Record the pressures and temperatures again.
  3. Turn the engine OFF. Compare the low and high side pressures and the output temperatures to the A/C Performance table below.

Does all the recorded data fall within the specified ranges of the A/C Performance table below?

--

Go to Step 10

Go to Step 6

6

Compare the recorded pressures to A/C System Pressure-Zone Classification .

Do both the low and high side pressures fall within Zone A on the chart?

--

Go to Cooling Insufficient, A/C System - Pressure Zone A

Go to Step 7

7

Do the pressures fall within Zone B?

--

Go to Cooling Insufficient, A/C System - Pressure Zone B

Go to Step 8

8

Do the pressures fall within Zone C?

--

Go to Cooling Insufficient, A/C System - Pressure Zone C

Go to Step 9

9

Do the pressures fall within Zone D?

--

Go to Cooling Insufficient, A/C System - Pressure Zone D

Go to Step 10

10

Operate the system in order to verify the repair.

Did you correct the condition?

--

Go to Step 11

Go to Symptoms in HVAC System - Manual or Symptoms in HVAC System - Automatic

11

  1. Disconnect the J 39500-B .
  2. Install the left diagonal brace. Refer to Front End Sheet Metal Diagonal Brace Replacement in Body Front End.

Is the action complete?

--

System OK

--

A/C System Pressure-Zone Classification


Object Number: 634265  Size: MF

A/C Performance Table

Relative Humidity

Ambient Air Temperature

Maximum Low Side Pressure

Engine Speed

Maximum Right Center Air Outlet Temperature

Maximum High Side Pressure

%

°F

°C

PSI

kPa

RPM

°F

°C

PSI

kPa

20

70

21

37

255

2000

46

8

225

1551

80

27

37

255

47

8

275

1896

90

32

37

255

53

12

325

2241

100

38

38

262

54

12

325

2241

30

70

21

37

255

2000

48

9

240

1655

80

27

37

255

50

10

285

1965

90

32

39

269

57

14

340

2344

100

38

43

296

60

16

360

2482

40

70

21

37

255

2000

49

9

260

1793

80

27

37

255

53

12

305

2103

90

32

42

290

60

16

355

3137

100

38

49

338

66

19

395

2724

50

70

21

37

255

2000

51

11

275

1896

80

27

39

269

56

13

320

2206

90

32

46

317

63

17

375

2586

100

38

55

379

72

22

430

2965

60

70

21

37

255

2000

53

12

290

2000

80

27

42

290

59

15

340

2344

90

32

49

338

66

19

390

2689

100

38

60

414

78

26

445

3068

70

70

21

37

255

2000

55

13

305

2103

80

27

45

310

62

17

355

2448

90

32

53

365

70

21

405

2792

80

70

21

41

283

2000

56

13

320

2206

80

27

48

331

65

18

370

2551

90

32

57

393

73

23

420

2896

90

70

21

45

310

2000

58

14

335

2310

80

27

52

359

68

20

385

2655