VDOT Air Conditioning (A/C) System Diagnosis. Chevrolet Corvette 1997

For 1990-2009 cars only

Makes 🢒 Chevrolet 🢒 1997 🢒 Corvette 🢒 HVAC 🢒 HVAC Systems - Manual 🢒 VDOT Air Conditioning (A/C) System Diagnosis

VDOT A/C System Diagnosis

The V7 compressor is a variable displacement compressor that matches the air conditioning demand by changing the compressor stroke, instead of cycling the compressor clutch. A control valve located in the rear head of the compressor senses the low side pressure and causes the compressor mechanism to stroke. Because the V7 compressor always runs and the system does not cycle, these diagnostic procedures differ from those used for fixed displacement systems.

Preliminary Checks

•	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 operation of the cooling fans and repair as necessary.

•	Check the condenser for restricted air flow and clean as necessary.

The A/C system is operating properly if the discharge air temperature and compressor pressures are equal to those in the System Performance Test .

Refer to the following tables when you are diagnosing VDOT A/C system insufficient cooling complaints.

VDOT Refrigerant Charge

Step	Action	Value(s)	Yes	No
DEFINITION: The A/C system is blowing warm air. Check the refrigerant for a low charge.
1	Were you sent here from the VDOT Diagnostic System Check?	--	Go to Step 2	Go to System Performance Test
2	With the ignition OFF, connect the A/C gages. Are the high and low side pressures equal to and above the value specified?	345 kPa (50 psi)	Go to the Compressor Clutch Engagement table.	Go to Step 3
3	Add 0.45 kg (1 lb of R-134a.) Check the system for leaks. Is there a leak?	--	Go to Step 6	Go to Step 4
4	Are the high and low side pressures between the value specified?	207-345 kPa (30-50 psi)	System OK	Go to Step 5
5	Repair the leak. Is the repair done?	--	Go to Step 6	--
6	Evacuate and charge the A/C system. Are the high and low side pressures above the value specified?	345 kPa (50 psi)	System OK	Go to the Compressor Clutch Engagement table.

Compressor Clutch Engagement

Step	Action	Value(s)	Yes	No
DEFINITION: The A/C system is blowing warm air. Check the compressor clutch for engagement.
1	Were you sent here from the VDOT Refrigerant Charge Diagnostic Table?	--	Go to Step 2	Go to System Performance Test
2	Let the engine run at idle speed. Set the A/C control head in the UPPER mode. Set the blower motor speed to high. Set the temperature control to full cold. Push the A/C button to turn the A/C ON. Does the clutch engage?	--	Go to Step 3	Go to Step 11
3	Check for noise coming from the compressor or the A/C drive belt area. Is there noise coming from the compressor or the belt?	--	Go to Step 4	Go to the VDOT System Performance table.
4	Is the noise due to belt slippage?	--	Go to Step 5	Go to Step 6
5	Replace the belt. Is the repair complete?	--	System OK	Go to Step 9
6	Is the noise coming from the compressor?	--	Go to Step 7	Go to Step 9
7	Check the A/C lines for contact with other components. Is there contact with other components?	--	Go to Step 8	Go to Step 9
8	Reposition or replace the A/C lines as necessary. Is the repair complete?	--	System OK	Go to the VDOT System Performance table.
9	Refer to A/C system noise diagnosis. Is the noise coming from the compressor?	--	Go to Step 10	Go to the VDOT System Performance table.
10	Replace the compressor. Is the noise still present?	--	Go to the VDOT System Performance table.	System OK
11	Turn the ignition OFF. Disconnect the clutch wires at the compressor. Connect a jumper wire form ground to one of the compressor clutch terminals. Connect a fused-jumper wire from the positive battery post to the other compressor clutch terminal. Does the clutch engage?	--	Go to Step 12	Go to Step 13
12	Repair the electrical circuit to the compressor clutch. Let the engine run at idle speed. Set the A/C control head in the A/C mode. Set the blower motor speed to high. Set the temperature control to full cold. Does the clutch engage?	--	System OK	Go to the VDOT System Performance table.
13	Replace the clutch coil. Is the repair complete?	--	System OK	Go to the VDOT System Performance table.

VDOT System Performance

Step	Action	Value(s)	Yes	No
DEFINITION: The A/C system is blowing warm air. Checking the VDOT system performance.
1	Were you sent here from the Compressor Clutch Engagement Diagnostic Table?	--	Go to Step 2	Go to System Performance Test
2	Close all the vehicle windows and doors. Set A/C control head in the UPPER mode. Set the blower motor speed to high. Set the temperature control to full cold. Let the engine run at idle speed 5 minutes. Feel the liquid line on both sides of the expansion (orifice) tube. Push the A/C button to turn the A/C ON. Is the temperature the same on both sides of the expansion (orifice) tube the same?	--	Go to Step 3	Go to Step 8
3	Recover the refrigerant. Refer to refrigerant recovery. Check for a missing expansion (orifice) tube or O-ring. Is the expansion (orifice) tube or O-ring missing?	--	Go to Step 4	Go to Step 5
4	Replace the missing expansion (orifice) tube or O-ring. Is the repair complete?	--	Go to Step 6	--
5	Check for a restriction in the highside line. Is there a restriction?	--	Go to Step 7	--
6	Evacuate and charge the A/C system. Refer to Evacuation . Leak test the system. Check the discharge temperature. Is the discharge temperature within specs?	--	System OK	Go to Step 8
7	Repair the restriction in the highside line. Is the repair done?	--	System OK	--
8	Operate the A/C system for 5 minutes or longer. Record the low and high side pressures. On engines equipped with electric cooling fans, record the pressures with the fans ON. Locate the intersection of the low and high side pressures. Refer to the graphic/chart. Do the low and high side pressures intersect on the left side or right side of the chart?	--	If on the right side: Go to the High Side Pressure table.	If on the left side: Go to the Low Side Pressure table.

High Side Pressure

Step	Action	Value(s)	Yes	No
DEFINITION: Right area diagnosis and service.
1	Were you sent here from the VDOT System Performance Diagnostic Table?	--	Go to Step 2	Go to System Performance Test
2	Start the engine. Close all the vehicle doors and windows. Set the A/C control head in the UPPER mode. Set the blower motor speed to high. Set the temperature control to full cold. Push the A/C button to turn the A/C ON. Open the hood. Feel the liquid line between the condenser and the expansion tube. Is the liquid line cold?	--	Go to Step 3	Go to Step 7
3	Check the cooling fan(s). Are the cooling fan(s) operating?	--	Go to Step 4	Go to Step 5
4	Check the airflow at the condenser for restrictions. Is the airflow at the condenser restricted?	--	Go to Step 6	Go to System Performance Test
5	Repair or replace the cooling fan(s) as necessary. Is the repair complete?	--	System OK	--
6	Remove the restriction. Is the repair complete?	--	System OK	--
7	Check the A/C system for an overcharge of refrigerant. Is the A/C system overcharged?	--	Go to Step 8	Go to Step 9
8	Recover the refrigerant. Refer to Refrigerant Recovery and Recharging . Evacuate and charge the A/C system. Refer to Evacuation and Air Conditioning (A/C) Charging Using ACR4 . Is the repair complete?	--	System OK	Go to System Performance Test
9	Check for air in the A/C system. Is there air in the A/C system?	--	Go to Step 10	Go to System Performance Test
10	Leak test the A/C system. Refer to Leak Testing . Is there a leak in the A/C system?	--	Go to Step 11	Go to System Performance Test
11	Recover the refrigerant. Refer to Refrigerant Recovery and Recharging . Repair the leak in the A/C system. Evacuate and charge the A/C system. Refer to Evacuation and Air Conditioning (A/C) Charging Using ACR4 . Is the repair complete?	--	System OK	--

Low Side Pressure

Step

Action

Value(s)

Yes

DEFINITION: Left area diagnosis and service.

Were you sent here from the VDOT System Performance Diagnostic Table?

Go to Step 2

Go to System Performance Test

With the engine running, connect high and low side pressure gages.

Are the high and low side pressures within the values shown?

207 kPa (30 psi)

Go to Step 3

Go to Step 8

Close all the vehicle doors and windows.
Run the engine at 2000 rpm.
Set the temperature control to full cold.
Set the blower motor speed to high.
Cycle the mode knob from vent to A/C every 20 seconds for 3 minutes.

Are the high and low side pressures within the value shown?

207 kPa (30 psi)

Go to Step 4

Check for the following:

•	There is a slow rise in pressure in both the low and high side gages.

•	The compressor suction line is warm.

•	The discharge line is very hot.

Do all of the above conditions exist.

Go to Step 5

Go to Step 6

Replace the compressor.

Is the repair complete?

System OK

Turn the engine OFF.

With the compressor clutch disengaged, does the compressor clutch driver (not the pulley) turn freely by hand?

Go to Step 5

Go to Step 7

Check the low side pressure.

Is there a rapid rise in the low side pressure with the engine rpm between the value(s) shown?

2000 and 2800 rpm

Go to the Control Valve table.

Go to Step 5

Is the low side pressure within the values shown?

172 to 241 kPa 27 to 38 psi

Go to Step 9

Go to the Control Valve table.

Feel the liquid line before the expansion (orifice) tube.

Is the liquid cold?

Go to Step 10

Go to Step 12

Check the liquid line for a restriction before the expansion (orifice) tube.

Is there a restriction in the liquid line before the expansion (orifice) tube?

Go to Step 11

Go to System Performance Test

Repair the restriction or replace the liquid line before the expansion (orifice) tube.

Is the repair complete?

System OK

Go to System Performance Test

Add 0.40 kg (14 oz) of refrigerant to the system.

Does the cooling improve?

Go to Step 13

Go to Step 15

Perform a leak test. Refer to Leak Testing.

Is there a leak?

Go to Step 14

System OK

Repair the leak.
Evacuate and Charge the A/C system. Refer to Evacuation and Air Conditioning (A/C) Charging Using ACR4 .

Is the repair complete?

System OK

Recover the refrigerant. Refer to Refrigerant Recovery and Recharging .
Check the expansion (orifice) tube.

Is the expansion (orifice) tube plugged?

Go to Step 16

Remove and clean or replace the expansion (orifice) tube as necessary.

Is the repair complete?

Go to Step 17

Evacuate and charge the A/C system. Refer to Evacuation and Air Conditioning (A/C) Charging Using ACR4 .

Is the repair complete?

System OK

Go to System Performance Test

Control Valve

Step	Action	Value(s)	Yes	No
DEFINITION: The VDOT control valve is inoperative.
1	Were you sent here from the Low Side Pressure Diagnostic Table?	--	Go to Step 2	Go to System Performance Test
2	Connect high and low side pressure gages. Close all the vehicle doors and windows. Run the engine at 2000 rpm for 5 minuets. Set the A/C control head to the UPPER mode. Set the temperature control to full cold. Push the A/C button to turn the A/C ON. Set the blower motor speed on low. Is the low side pressure within the value(s) shown.	172 to 241 kPa (25 to 35 psi)	Go to System Performance Test	Go to Step 3
3	Recover the refrigerant. Refer to Refrigerant Recovery and Recharging . Replace the control valve. Is the repair complete?	--	Go to Step 4	--
4	Evacuate and charge the A/C system. Refer to Evacuation and Air Conditioning (A/C) Charging Using ACR4 . Is the repair complete?	--	System OK	Go to System Performance Test