GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2000 🢒 GMC C Pickup - 2WD 🢒 HVAC 🢒 Heating, Ventilation and Air Conditioning 🢒 Cooling Insufficient - Air Conditioning (A/C) Inoperative
Table 1: Gray Area Diagnosis and Service
Table 2: Striped Area Diagnosis and Service

The compressor is a scroll compressor that matches the air conditioning demand by changing the compressor stroke, instead of cycling the compressor clutch. A capacity control valve located in the compressor senses the low side pressure and causes the compressor to adjust to A/C cooling demands. The compressor always runs and the system does not cycle. However, the compressor may cycle if the cooling load is not reduced enough by the capacity control valve.

Preliminary Checks
    • Check the proper operation of the cooling fans.
    • Check for system voltage above 10.5 Volts.
    • Check the A/C fuse and replace as necessary.
    • Check the A/C blower operation and repair as necessary.
    • Check the clutch coil electrical connection and repair as necessary.
    • Check the drive belt and replace if damaged or missing.
    • Check the condenser for restricted air flow and clean as necessary.

Refer to the following tables when you are diagnosing insufficient cooling complaints.

Step

Action

Value(s)

Yes

No

1

Inspect for any stored DTCs.

Are any DTCs stored?

--

Go to Step 3

Go to Step 2

2

Connect the J 39500-B .

Are the pressures above 350 kPa (50 psi)?

--

Go to Step 4

Go to Step 8

3

Correct any stored DTCs.

Does the complaint persist?

--

Go to Step 1

System OK

4

Inspect and correct for a blown Air Conditioner (A/C) fuse.

Does the complaint persist?

--

Go to Step 5

System OK

5
  1. Disconnect the A/C clutch connector.
  2. Inspect the A/C clutch for proper rotation.

Does the A/C clutch rotate smoothly?

--

Go to Step 6

System OK

6

Inspect and correct for the following conditions:

    • Proper operation of the cooling fans.
    • Condenser restrictions
    • Radiator restrictions

Does the complaint persist?

--

Go to Step 7

Go to: Air Conditioning Compressor Replacement

7

Read the DCS for Bulletins and Hints.

Follow the procedures indicated.

Does the complaint persist?

--

Go to Step 10

System OK

8
  1. Add 0.453 kg (1 lb) of refrigerant.
  2. Perform a leak check. Refer to Leak Testing .

Did you find a leak?

--

Go to Step 9

Go to Step 10

9
  1. Repair the leak.
  2. Inspect the system performance. Refer to System Performance Test .

Does the complaint persist?

--

Go to Step 2

System OK

10

Perform an A/C Performance Check using the following steps:

  1. Ensure that the ambient temperature is at least 6°C (43°F).
  2. Ensure that the engine is idling at normal operating temperature.
  3. Turn the A/C to the ON position.
  4. Select the coldest setting.
  5. Select the MAX blower speed.
  6. Record the A/C pressures.
  7. Record the A/C temperatures.
  8. Refer to System Performance Test .

Does the A/C performance meet the requirement on the Performance Chart?

--

Go to Step 11

Go to HVAC High Side vs. Low Side Pressure Table

11

Was the customer complaint made due to high temperature and/or high humidity?

--

System OK

Go to Step 12

12

Perform a leak test. Refer to Leak Testing .

Did you find a leak?

--

Go to Step 13

System OK

13

Evacuate and recharge the A/C system. Refer to Refrigerant Recovery and Recharging .

Does the complaint persist?

--

Go to Step 10

System OK

High Side vs. Low Side Pressure Table
Object Number: 247012 Size: LF

Gray Area Diagnosis and Service

Problem

Action

Important: The clutch may cycle if the discharge pressure exceeds 2758 kPa (400 psi) or if system voltage drops below 10.5 Volts.

Improper condenser operation

Improper condenser operation may result from one of the following causes:

    • Extremely high ambient humidity
    • Insufficient air flow across condenser
    • Damaged or dirty condenser fins
    • Improper cooling fan operation

High side refrigerant restriction
  1. Feel liquid line before expansion tube (orifice). A cold line indicates restriction in the high side.
  2. Inspect for a frost spot in order to locate the restriction.
  3. Repair the line as necessary.

Refrigerant system overcharged (high discharge and high suction pressures)

The clutch may cycle ON/OFF and cause compressor noise.

Evacuate and recharge the system with the proper amount of refrigerant. Refer to Refrigerant Recovery and Recharging .

Expansion tube (orifice) blocked
  1. Discharge the system slowly using the low pressure service port to prevent oil loss.
  2. Inspect the expansion (orifice) tube for blockage. Clean or replace the tube as required. Refer to Expansion (Orifice) Tube Replacement .
  3. Evacuate the system to a vacuum. Improper evacuation of the system prior to recharge will cause air to remain in the system.
  4. Recharge the system with the proper amount of refrigerant. Refer to Refrigerant Recovery and Recharging .
  5. Leak test the system. Refer to Leak Testing .

Air in system (High discharge and high suction pressures)
  1. Discharge the refrigerant system slowly using the low pressure service port to prevent oil loss.
  2. Inspect the expansion (orifice) tube for blockage. Clean or replace the tube as required. Refer to Expansion (Orifice) Tube Replacement .
  3. Evacuate the system to a vacuum. Improper evacuation of the system prior to recharge will cause air to remain in the system.
  4. Recharge the system with the proper amount of refrigerant. Refer to Refrigerant Recovery and Recharging .
  5. Leak test the system. Refer to Leak Testing .

Striped Area Diagnosis and Service

Problem

Action

The compressor is damaged internally.
    • If suction and discharge pressure are equal and do not change when the A/C mode is turned ON and OFF, the compressor may be internally damaged.
    • Excess heat at the clutch surfaces or a free wheeling clutch driver are signs of internal compressor damage.
    • When replacing the compressor, refer to: Air Conditioning Compressor Replacement

The expansion tube (orifice) is missing.

Feel the liquid line after the expansion tube. If the line is warm, discharge the system and inspect for proper installation of the expansion tube. If the expansion tube or O-ring is missing, replace the expansion tube. Refer to Expansion (Orifice) Tube Replacement .

The refrigerant system is undercharged.
  1. The refrigerant may be undercharged when the suction pressure is below 35 psi during the high load test.
  2. The suction line before the accumulator will be warm if the charge is low.
  3. Add 1 lb of refrigerant.
  4. Recheck the pressure. Verify that the pressure is in the white area on the chart. Then find and correct the leak.
  5. Evacuate the system. Refer to Refrigerant Recovery and Recharging .
  6. Charge the system with the correct amount of refrigerant.

The expansion tube (orifice) is blocked.
  1. Discharge the system slowly using the low pressure service port to prevent oil loss. Refer to Refrigerant Recovery and Recharging .
  2. Inspect the expansion (orifice) tube for blockage. Clean or replace the tube as required. Refer to Expansion (Orifice) Tube Replacement .
  3. Evacuate the system to a vacuum. Improper evacuation of the system prior to recharge will cause air to remain in the system.
  4. Recharge the system with the proper amount of refrigerant. Refer to Refrigerant Recovery and Recharging .
  5. Leak test the system. Refer to Leak Testing .