VDOT Air Conditioning (A/C) System Diagnosis. GMC Truck Jimmy

For 1990-2009 cars only

Makes 🢒 GMC_Truck 🢒 2000 🢒 Jimmy - 4WD 🢒 HVAC 🢒 Heating, Ventilation and Air Conditioning 🢒 VDOT Air Conditioning (A/C) System Diagnosis

The following chart will help you to diagnose V7 compressor and VDOT refrigerant system problems that cause insufficient cooling. Use the chart in conjunction with other appropriate service manual information.

The V7 compressor is a variable displacement compressor. The compressor matches air conditioning demand by changing stroke instead of cycling the clutch. A control valve that is located in the rear head of the compressor senses compressor low side pressure. The valve then causes the compressor mechanism to change stroke. These diagnostic procedures differ from those used for fixed displacement systems because the V7 compressor always runs and the system does not cycle. Use these procedures in order to avoid needlessly replacing A/C components.

If the discharge air temperature with the A/C is normal after you make the following repairs, then the system operates properly. Repair the following components as necessary:

•

The fuse

•	The blower motor operation

Refer to Blower Motor and Fan Replacement .

•	The clutch coil and the rear head switch(es) connections

•	The compressor belt

Adjust or replace the belt if the belt is damaged or missing.

•	Engine cooling fan clutch operation

Refer to Fan Clutch Replacement in Engine Cooling.

•	Inspect the condenser for restricted air flow.

Step

Action

Value(s)

Yes

Important: Before you proceed with this step, perform the following steps:

•	Properly calibrate the pressure gauges.

•	Ensure that the ambient air temperature is 15.5°C (60°F) or higher.

•	Warm the engine to the operating temperature.

Turn OFF the ignition key.
Connect a high pressure gauge and a low pressure gauge.
Ensure that the pressures are approximately equal.

Are both pressures above 50 psi (345 kPa)?

Go to Step 8

Go to Step 2

Are both pressures below 10 psi (69 kPa)?

Go to Step 3

Go to Step 5

Add 1 lb of R-134a. Inspect the system for leaks.

Did you find a leak?

Go to Step 4

System OK

Recover the system.
Repair the leak.
Evacuate the system.
Charge the system. Refer to Refrigerant Recovery and Recharging .

Is the repair complete?

System OK

Are both pressures within 10-50 psi (69-345 kPa)?

Go to Step 6

Go to Step 8

Inspect the system. Add R-134a if necessary.

Is a leak found?

Go to Step 7

System OK

Recover the system.
Repair the leak.
Evacuate the system.
Charge the system. Refer to Refrigerant Recovery and Recharging .

Is the repair complete?

System OK

Run the engine at idle.
Set the A/C controls to the following settings:

•	NORM A/C mode

•	HIGH blower

•	Full COLD temperature

Did the clutch engage?

Go to Step 13

Go to Step 9

Turn OFF the ignition.
Disconnect the clutch wires at the compressor.
Connect a jumper wire from ground to one compressor clutch terminal.
Connect a fused-jump wire from the positive battery post to the other compressor clutch terminal.
Run the engine at idle.

Did the clutch engage?

Go to Step 11

Go to Step 10

Replace the clutch coil.

Is the repair complete?

System OK

Repair the electrical circuit to the compressor clutch.

Is the repair complete?

Go to Step 12

Run the engine at idle.
Set the A/C controls to the following settings:

•	NORM A/C mode

•	HIGH blower

•	Full COLD temperature

Did the clutch engage?

System OK

Do you hear a loud underhood knocking noise from the compressor and/or did the belt slip?

Go to Step 14

Go to Step 15

Recover the system. Refer to Refrigerant Recovery and Recharging .
Replace the compressor. Refer to Air Conditioning Compressor Replacement .

Is the repair complete?

Go to Step 15

Evacuate the system.
Charge the system. Refer to Refrigerant Recovery and Recharging .
Perform a leak test. Refer to Leak Testing .

Is a leak detected?

Go to Step 16

Go to Step 17

Repair the leak.

Is the repair complete?

Go to Step 17

Important: This test is designed for the following typical garage conditions:

•	21-32°C (70-90°F) temperature

•	No sun load

Normal discharge air temperature is at least 7°C (20°F) cooler than the ambient temperature. Follow the test directions exactly. The test is designed to create enough cooling load to cause the V7 compressor to operate at full stroke. This is necessary for accurate test results.

Close all of the vehicle doors and the windows.
Set the A/C controls to the following settings:

•	NORM A/C mode

•	HIGH blower

•	Full COLD temperature

Run the engine at idle for 5 minutes.
Feel the liquid line on both sides of the orifice (expansion) tube.

Do you feel a temperature difference?

Go to Step 18

Go to Step 19

Operate the A/C system for 5 minutes or more.
Record the low side pressure and the high side pressure.
Locate the intersection of the low and high side pressures. Refer to Low and High Side Pressure Relationship Chart .

Did you locate the intersection?

Go to Step 24

Recover the system. Refer to Refrigerant Recovery and Recharging .
Inspect the system.

Is the orifice (expansion) tube missing?

Go to Step 20

Install an orifice (expansion) tube.

Is the repair complete?

Go to Step 21

Evacuate the system.
Charge the system. Refer to Refrigerant Recovery and Recharging .
Perform a leak test. Refer to Leak Testing .

Did you detect a leak?

Go to Step 22

Go to Step 23

Repair the leak.

Is the repair complete?

Go to Step 23

Note the discharge air temperature.

Is the discharge air temperature within specifications?

Go to Step 17

Refer to Low and High Side Pressure Relationship Chart .

Do the high and low side pressures intersect in the white area of the chart?

System OK

Go to Step 25

Refer to Low and High Side Pressure Relationship Chart .

Do the high and low side pressures intersect in the gray area of the chart?

Go to Step 27

Go to Step 26

Refer to Low and High Side Pressure Relationship Chart .

Do the high and low side pressures intersect in the striped area of the chart?

Go to Step 33

Ensure that the engine is still running.
Set the A/C controls to the following settings:

•	NORM A/C mode

•	HIGH blower

•	Full COLD temperature

Close the vehicle doors and the windows.
Open the hood.
Feel the liquid line between the condenser and the orifice (expansion) tube.

Is the tube cold?

Go to Step 28

Go to Step 29

Inspect for a restriction in the high side.
Recover the system. Refer to Refrigerant Recovery and Recharging .
Remove any restrictions.

Is the repair complete?

Go to Step 32

Inspect the system for refrigerant overcharge or air in the system.

Did you detect a condition?

Go to Step 30

Recover the system. Refer to Refrigerant Recovery and Recharging .

Is the procedure complete?

Go to Step 31

Evacuate the system.
Charge the system. Refer to Refrigerant Recovery and Recharging .
Perform a leak test. Refer to Leak Testing .

Did you detect a leak?

Go to Step 32

Repair any leaks.

Is the repair complete?

Go to Step 17

Are the compressor high and low side pressures within 206.8 kPa (30 psi) of each other?

Go to Step 38

Go to Step 34

Is the low side pressure within the specified range?

172.4-241.3 kPa (25-35 psi)

Go to Step 35

Go to Step 43

The refrigerant is undercharged. Add 0.396 kg (14 oz) of refrigerant to the system.

Does the cooling performance improve?

Go to Step 41

Go to Step 36

Recover the system. Refer to Refrigerant Recovery and Recharging .
Inspect the orifice (expansion) tube.

Is the tube plugged?

Go to Step 37

Go to Step 38

Clear the tube lines.
Replace the orifice (expansion) tube. If there is only a light debris, clean the tube with compressed air.

Is the repair complete?

Go to Step 41

Run the engine at 3,000 RPM.
Set the A/C controls to the following settings:

•	High blower

•	Full COLD temperature

Close the vehicle doors and the windows.
Cycle the mode knob from VENT to A/C every 20 seconds for 3 minutes.

Are the compressor high and low side pressures within 206.8 kPa (30 psi) of each other?

Go to Step 39

Go to Step 17

Turn OFF the engine. Ensure that the compressor clutch is disengaged.

Does the compressor clutch driver (not the pulley) turn freely when spun by hand?

Go to Step 40

Go to Step 43

Replace the compressor. Refer to Air Conditioning Compressor Replacement .

Is the repair complete?

Go to Step 41

Evacuate the system.
Charge the system.
Perform a leak test.

Did you detect a leak?

Go to Step 42

Go to Step 17

Repair the leak.

Is the repair complete?

Go to Step 17

Important: Follow this test procedure exactly. The test is designed to create a low cooling load in order to cause the V7 compressor to operate at less than full stroke. This is necessary for accurate test results.