GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 1998 🢒 Yukon - 4WD 🢒 HVAC 🢒 HVAC Systems - Manual 🢒 CCOT Air Conditioning (A/C) System Diagnosis

Step

Action

Value(s)

Yes

No

1

Inspect the following components of the A/C system:

    • The fuses
    • The wire connectors
    • The blower fan operation

Did you find and repair a condition?

--

System OK

Go to Step 2

2

Is the drive belt loose, missing, or damaged?

--

Go to Step 4

Go to Step 3

3

Important: The ambient temperature must be above 10°C (50°F) for completion of this diagnostic procedure.

Inspect the compressor clutch engagement by following these steps:

  1. Start the engine.
  2. Idle the engine at approximately 1000 RPM.
  3. Set the A/C control assembly to the NORM position.
  4. Set the blower to the HIGH position.
  5. Place an auxiliary fan in front of the vehicle.
  6. Observe the clutch operation for a period of 5 minutes.

Does the clutch engage or cycle?

--

Go to Step 7

Go to Step 11

4

Has the compressor seized?

--

Go to Step 5

Go to Step 6

5
  1. Replace the compressor assembly.
  2. Replace the orifice.
  3. Recover the refrigerant.
  4. Evacuate the system.
  5. Charge the system.

Does the air conditioning system operate properly?

--

System OK

Go to Step 6

6

Tighten or replace the belt, as needed.

Does the air conditioning system operate properly?

--

System OK

Go to Step 3

7

Feel the liquid line before the orifice tube.

Is the liquid line cold?

--

Go to Step 8

Go to Step 9

8
  1. Inspect the high side of the system for a frost spot in order to locate a restriction.
  2. Repair the restriction.
  3. Recover the refrigerant.
  4. Evacuate the system.
  5. Charge the system.

Is the air condition system operating properly?

--

System OK

Go to Step 9

9
  1. Feel the evaporator inlet pipe.
  2. Feel the evaporator outlet pipe.

Is the inlet pipe colder than the outlet pipe?

--

Go to Step 10

Go to Step 24

10
  1. Conduct a leak test of the system. Refer to Vacuum System .
  2. Repair any leaks, as necessary.
  3. If you repaired a leak, complete the following steps:
    4. 3.1. Recover the refrigerant.
    3.2. Evacuate the system.
    3.3. Charge the system.

Is the air condition system operating properly?

--

System OK

Go to Step 20

11
  1. Connect a fused jumper wire from the compressor hot lead to the positive battery post.
  2. Observe the compressor operation.

Does the compressor clutch engage?

--

Go to Step 12

Go to Step 18

12
  1. Remove the jumper.
  2. Measure the pressure at the accumulator fitting.

Is the pressure below the specified value?

345 kPa (50 psi)

Go to Step 13

Go to Step 15

13

Measure the refrigerant pressure on the high side of the system.

Is the pressure above the specified value?

345 kPa (50 psi)

Go to Step 14

Go to Step 10

14
  1. Recover the refrigerant.
  2. Inspect for the following conditions:
    3. 2.1. A plugged orifice
    2.2. A restriction in the high side of the system
  3. Complete the necessary repairs, or replace the orifice.
  4. Evacuate the system.
  5. Charge the system.

Is the air condition system operating properly?

--

System OK

Go to Step 10

15

Connect a fused jumper wire between the pressure switch and the positive battery post.

Does the compressor operate?

--

Go to Step 16

Go to Step 17

16

Important: Do not recover the refrigerant. The fitting has a Schrader Valve®.

Replace the pressure switch.

Is the air condition system operating properly?

--

System OK

Go to Step 7

17
  1. Inspect the pressure switch for an open circuit or a broken wire.
  2. Complete any necessary repairs.

Is the air condition system operating properly?

--

System OK

Go to Step 7

18

Apply an external ground to the compressor.

Does the compressor clutch engage?

--

System OK

Go to Step 19

19

Rebuild the compressor.

Is the air condition system operating properly?

--

System OK

Go to Step 12

20
  1. Add 0.45 kg (1 lb) of refrigerant to the system.
  2. Inspect the clutch cycle rate.

Is the clutch cycle rate greater than the specified value?

8 cycles/minute

Go to Step 21

Go to Step 22

21
  1. Recover the refrigerant.
  2. Inspect the system for a plugged orifice.
  3. Repair the orifice as necessary.
  4. Evacuate the system.
  5. Charge the system.

Does the air conditioning system operate properly?

--

System OK

Go to Step 11

22
  1. Feel the evaporator inlet pipe.
  2. Feel the evaporator outlet pipe.

Is the inlet pipe colder than the outlet pipe?

--

Go to Step 23

System OK

23
  1. Add 0.45 kg (1 lb) of refrigerant to the system.
  2. Feel the evaporator inlet pipe.
  3. Feel the evaporator outlet pipe.

Is the inlet pipe colder than the outlet pipe?

--

Go to Step 21

System OK

24
  1. Install a gauge set.
  2. Inspect the compressor cycling pressure.

Does the compressor cycle on within the specified value range?

280-350 kPa (41-51 psi)

Go to Step 25

Go to Step 27

25

Does the compressor cycle off within the specified value range?

140-190 kPa (20-28 psi)

Go to Step 26

Go to Step 27

26
  1. Set the A/C control assembly to the MAX position.
  2. Set the temperature setting to full cold position.
  3. Set the blower to the HIGH position.
  4. Stabilize the engine speed for 5 minutes.
  5. Install a thermometer in the A/C outlet.
  6. Perform the Performance Test. Refer to System Performance Test .

Is the temperature performance within the limits of the test specifications?

--

System OK

Go to Step 10

27

Does the compressor cycle high on above the specified value?

350 kPa (51 psi)

Go to Step 28

Go to Step 29

28

Does the compressor cycle OFF below the specified value?

140 kPa (20 psi)

Go to Step 16

Go to Step 29

29
  1. Disconnect the blower wire.
  2. Determine when the compressor cycles OFF.

Does the compressor cycle off below the specified value range?

140 kPa (20 psi)

Go to Step 16

Go to Step 30

30

Reconnect the blower motor wire.

Is the wire reconnected?

--

Go to Step 26

--

31

Observe the compressor cycling.

Does the compressor cycle ON continuously?

--

Go to Step 32

Go to Step 21

32
  1. Recover the refrigerant.
  2. Inspect the orifice.

Is the orifice missing?

--

Go to Step 33

Go to Step 34

33
  1. Install the orifice.
  2. Evacuate the system.
  3. Charge the system.

Does the air conditioning system operate properly?

--

System OK

Go to Step 34

34

Inspect the suction line.

Is the suction line restricted?

--

Go to Step 35

Go to Step 36

35
  1. Repair the suction line, as required.
  2. Evacuate the system.
  3. Charge the system.

Does the air conditioning system operate properly?

--

System OK

Go to Step 36

36
  1. Evacuate the system
  2. Charge the system

Does the air conditioning system operate properly?

--

System OK

--