GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 1998 🢒 Jimmy - 2WD 🢒 HVAC 🢒 HVAC Systems - Manual 🢒 System Performance Test

Perform the following test if you suspect a malfunction in the refrigerant system due to abnormal system pressures.

Tools Required

J 21213-A Four Jack Dual Range Temperature Tester

  1. Park the vehicle inside, or in a shaded area.
  2. Open the doors or the windows of the vehicle.
  3. Vent the engine exhaust if necessary.
  4. Open the hood.
  5. Install the high and low side pressure gauges.

    6. Route the lines over the rear hood seal. Tape the gauges to the windshield in order to view the gauges.

  6. Close the hood to the safety latch position.
  7. Record the ambient temperature at the vehicle.

    8. Important: Ensure that you record the relative humidity and the ambient temperature conditions at the time of the test.

  8. Record the relative humidity.

    9. Use a psychrometer or consult the local weather bureau.

  9. Close the doors or the windows of the vehicle.
  10. Set the mode control to MAX A/C.
  11. Adjust the blower speed to HI.
  12. Adjust the temperature to full COLD.
  13. Open the air conditioning outlets.
  14. Install J 21213-A or an equivalent into the right center air conditioning outlet.
  15. Place the transmission in PARK or NEUTRAL.
  16. Start the engine.
  17. Stabilize the engine speed at 1500 RPM.

    18. Start the timer.

  18. Run the air conditioning system until the outlet air reaches the lowest temperature (about 3 minutes).
  19. Record the following statistics:
    20. • The outlet air temperature
    • The high-side pressure
    • The low side-pressure
  20. Turn off the engine.
  21. Compare the readings. Normal operating air conditioning systems should not exceed normal levels.
  22. Inspect the outer surfaces of the radiator and the condenser cores.

    23. Inspect between the condenser and the radiator as well as the outer surfaces. Ensure that the airflow is not blocked by the following materials:

    • Dirt
    • Leaves
    • Other foreign matter
  23. Inspect the following components for restrictions or kinks:
    24. • The evaporator core
    • The condenser core
    • The hoses
    • The tubes
  24. Inspect for refrigerant leaks.
  25. Inspect all of the air ducts for leaks or restrictions.

    26. Low air flow may indicate a restricted evaporator core.

  26. Inspect the compressor clutch for slippage.
  27. Inspect the drive belt for improper tension.

If you do not find a problem in the CCOT system, refer to CCOT Air Conditioning (A/C) System Diagnosis .

Relative Humidity

Ambient Air Temperature

Maximum Low Side Pressure

Engine Speed

Maximum Center Air Outlet Temperature

Maximum High Side Pressure

40%

26.7°C

(80°F)

220 kPa

(32 psi)

1500 RPM

10.6°C

(51°F)

1 572 kPa

(228 psi)

26.7°C

(90°F)

268 kPa

(39 psi)

10.6°C

59°F

1 931 kPa

(280 psi)

37.8°C

(100°F)

308 kPa

(44 psi)

18.9°C

(66°F)

2 075 kPa

301 psi

43.3°C

(110°F)

317 kPa

(46 psi)

23.9°C

(75°F)

2 255 kPa

(327 psi)

48.9°C¹

(120°F)¹

310 kPa¹

(45 psi)¹

17.2°C¹

(63°F)¹

2 530 kPa¹

(367 psi)¹

50%

21.1°C²

(70°F)²

193 kPa²

(28 psi)²

6.1°C²

(43°F)²

1 103 kPa²

(160°F)²

70%

21.1°C

(70°F)

234 kPa

(34 psi)

12.2°C

(54°F)

1 572 kPa

(228 psi)

32.2°C

(90°F)

324 kPa

(47 psi)

18.3°C

(65°F)

2 006 kPa

291 psi

80%

26.7°C

(80°F)

268 kPa

39 psi

14.4°C

58°F)

1 731 kPa

(251 psi)

¹Measure these values in MAX A/C with all of the windows closed.

²The compressor cycles ON and OFF.