GM Service Manual Online
For 1990-2009 cars only
Table 1: A/C Performance Table
Table 2: Refrigerant-134a Pressure-Temperature Relationship

Important: 

   • Before carrying out the high/low pressure and centre vent temperature testing, make sure that the vehicles A/C system has no visual or operational defects and that all refrigerant recovery and recharging safety requirements are adhered to. Refer to Refrigerant Recovery and Recharging.
   • Before commencing the testing follow the vehicle set up procedure. Failure to correctly set the vehicle up for testing will provide inaccurate diagnosis when comparing actual pressure readings to the table below.


Object Number: 1950808  Size: SH
  1. Connect the calibrated high/low pressure gauges to the A/C system (1).
  2. Important: Both high and low pressures should be within 50kPa of each other, if not a blockage may be present in the system.

  3. Confirm that the static pressures (vehicle not started or A/C engaged) are correct.
  4. Important: When possible the vehicle should be tested in direct sunlight, especially in the case of climate control vehicles using solar sensors.

  5. Record the ambient temperature conditions and the relative humidity at the time of the test.
  6. DO NOT test the vehicle with the condenser air flow restricted, such as against a wall.

  7. Object Number: 1950812  Size: SH
  8. Set the blower motor speed control (1) to the highest blower motor speed.
  9. Set the temperature control (2) to the maximum cold setting.
  10. Set the air intake mode control (3) to fresh air intake mode.

  11. Object Number: 1950815  Size: SH
  12. Set the mode outlet control to the face position with the instrument panel louvres open and facing straight ahead.
  13. Important: Make sure that the thermometer probe is inserted to a length of approximately 50mm.

  14. Insert a thermometer centrally into the face vent.
  15. Turn the engine ON and run at idle speed.
  16. Close all vehicle doors and windows.
  17. Close the vehicle engine hood.
  18. Important: For Accurate testing the relative humidity percentage (RH%) should be known, as you will see the pressures and vent temperatures alter as RH% changes. Refer to the A/C performance table below.

  19. Make sure accurate pressure gauges are connected to the A/C system.
  20. Turn the engine OFF and compare the readings with the data in the A/C performance table. A normally operating A/C system should not exceed levels shown. If the readings exceed the table limits, refer to Symptoms - HVAC Systems - Manual.

A/C Performance Table

Engine Speed (RPM)

Relative Humidity (%)

Ambient Air Temperature

Centre Air Outlet Temperature

Gauge Pressure Low Side Pressure

Gauge Pressure High Side Pressure

°F

°C

°F

°C

psi

kPa

psi

kPa

Idle

20

59

15

37

3.00

27

162

142

943

68

20

37

3.00

31

185

168

1106

77

25

40

4.64

36

209

191

1296

86

30

47

8.60

42

236

225

1494

95

35

54

12.49

50

265

266

1653

104

40

62

16.45

58

300

304

1864

113

45

69

20.47

63

334

323

2155

40

59

15

37

3.00

25

171

139

956

68

20

38

3.50

28

197

164

1129

77

25

44

6.79

32

222

192

1323

86

30

52

11.27

36

252

209

1445

95

35

61

15.94

42

288

248

1709

104

40

69

20.76

48

329

279

1925

113

45

77

25.18

54

375

306

2110

60

59

15

37

3.00

26

177

140

966

68

20

40

4.47

30

205

166

1146

77

25

48

8.92

34

233

192

1326

86

30

57

13.93

39

269

215

1480

95

35

66

19.11

45

310

249

1718

104

40

76

24.59

52

358

300

2072

113

45

86

29.82

59

406

318

2196

80

59

15

37

3.00

27

186

142

976

68

20

43

6.11

31

214

168

1160

77

25

52

11.15

36

250

191

1320

86

30

62

16.95

42

289

225

1551

95

35

74

23.23

50

342

266

1833

104

40

85

29.27

58

398

304

2096

113

45

96

35.65

63

436

323

2226

Refrigerant-134a Pressure-Temperature Relationship

°C

°F

kPa

psig

°C

°F

kPa

psig

DEFINITION: This table indicates the pressure of the Refrigerant-134a at various temperatures. For instance, a drum of refrigerant at room temperature of 26.6°C (80°F) will have a pressure of 595.6 kPa (86.4 psi). If the refrigerant is heated to 51.6°C (125°F), the pressure will increase to 1278.8 kPa (185.5 psi). The refrigerant also can be used conversely in order to determine the temperature at which the Refrigerant-134a boils under various pressures. For example, at a pressure of 188.2 kPa (27.3 psi), the Refrigerant-134a boils at 0°C (32°F).

 

15.5

60

392.3

56.9

-23.3

-10

12.4

1.8

18.3

65

438.2

63.6

-20.5

-5

27.0

3.9

21.1

70

487.3

70.7

-17.7

0

43.2

6.3

23.8

75

539.7

78.3

15.0

5

60.8

8.8

26.6

80

595.6

86.4

-12.2

10

80.1

11.6

29.4

85

655.1

95.0

9.4

15

101.3

14.7

32.2

90

718.5

104.2

-6.6

20

124.3

18.0

35.0

95

785.6

113.9

-3.8

25

149.4

21.7

37.7

100

856.9

124.3

-1.1

30

176.6

25.6

40.5

105

932.3

135.2

0.0

32

188.2

27.3

43.3

110

1012.1

146.8

1.6

35

206.2

29.9

46.1

115

1096.4

159.0

4.4

40

238.0

34.5

48.8

120

1185.2

171.9

7.2

45

272.5

39.5

51.6

125

1278.8

185.5

10.0

50

309.5

44.9

54.4

130

1377.3

199.8

12.7

55

349.4

50.7

60.0

140

1589.6

230.5