VDOT Air Conditioning (A/C) System Diagnosis. Pontiac Firebird 1998

For 1990-2009 cars only

Makes 🢒 Pontiac 🢒 1998 🢒 Firebird 🢒 HVAC 🢒 HVAC Systems - Manual 🢒 VDOT Air Conditioning (A/C) System Diagnosis

Table 1:	VDOT Refrigerant Charge
Table 2:	Compressor Clutch Engagement
Table 3:	VDOT System Performance
Table 4:	High Side Pressure
Table 5:	Low Side Pressure
Table 6:	Control Valve

The V5 and V7 compressors are variable displacement compressors. The V5 and V7 compressors match the air conditioning demand by changing the compressor stroke instead of cycling the compressor clutch. A control valve is located in the rear head of the compressor. The control valve completes the following functions:

•	Senses the low side pressure.

•	Causes the compressor mechanism to change stroke.

Because the compressor always runs and the system does not cycle, these diagnostic procedures differ from procedures that are used for fixed displacement systems.

Preliminary Checks

•	Inspect the A/C fuse. Replace as necessary.

•	Inspect the A/C blower operation. Repair/replace as necessary.

•	Inspect the clutch coil electrical connection. Repair/replace as necessary.

•	Inspect the drive belt. Replace the drive belt if it is damaged or missing.

•	Inspect the operation of the cooling fans. Repair/replace as necessary.

•	Inspect the condenser for restricted air flow. Clean the condenser 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 the VDOT System Performance table
2	With the ignition in the OFF position, connect the A/C gauges. Are the high and low side pressures equal to (or) 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 within the specified range?	69-345 kPa (10-50 psi)	System OK	Go to Step 5
5	Repair the leak. Is the repair complete?	--	Go to Step 6	--
6	Recover and recharge the A/C system. Refer to Refrigerant Recovery and Recharging 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: A/C compressor clutch will not engage when an A/C request has been made and no Powertrain DTC's are set.
1	Were you sent here from the VDOT Refrigerant Charge Diagnostic Table?	--	Go to Step 2	Go to the VDOT System Performance table
2	Let the engine run at idle speed. Set the A/C control to the NORM A/C mode. Set the blower motor speed to high. Set the temperature control to full cold. Does the clutch engage?	--	Go to Step 3	Go to Step 12
3	Check for a knocking noise coming from the compressor. Cycle the compressor ON and OFF to verify the source of the noise. Is there noise coming from the compressor?	--	Go to Step 4	Go to the VDOT System Performance table
4	Inspect the A/C drive belt for slippage. Is the noise due to belt slippage?	--	Go to Step 5	Go to Step 6
5	Replace the A/C drive belt. Refer to Drive Belt Replacement in Engine Mechanical. Is the repair complete?	--	System OK	Go to Step 9
6	Listen to the compressor for the noise. 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	Recover and recharge the A/C system. Refer to Refrigerant Recovery and Recharging Is the repair complete?	--	System OK	Go to Step 10
10	Refer to the noise diagnosis table. Is the noise coming from the compressor?	--	Go to Step 11	Go to the VDOT System Performance table
11	Replace the A/C compressor. Refer to Air Conditioning Compressor Replacement . Is the noise still present?	--	Go to the VDOT System Performance table	System OK
12	Turn the ignition to the OFF position. Disconnect the clutch wires at the compressor. Connect a jumper wire from 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 13	Go to Step 14
13	Repair the electrical circuit to the compressor clutch. Run the engine at idle speed. Set the A/C control to 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
14	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 the VDOT System Performance table
2	Close all the vehicle windows and doors. Set the A/C control to NORM A/C mode. Set the blower motor speed to high. Set the temperature control to full cold. Let the engine run at idle speed for 5 minutes. Feel the liquid line on both sides of the expansion (orifice) tube. Is the temperature the same on both sides of the expansion (orifice) tube?	--	Go to Step 3	Go to Step 8
3	Recover the refrigerant. Refer to Refrigerant Recovery and Recharging . Inspect for a missing expansion (orifice) tube or O-ring. Is the expansion (orifice) tube or the O-ring missing?	--	Go to Step 4	Go to Step 5
4	Replace the missing expansion (orifice) tube or the O-ring. Is the repair complete?	--	Go to Step 6	--
5	Inspect for a restriction in the highside line. Is there a restriction?	--	Go to Step 7	--
6	Recover and recharge the A/C system. Refer to Refrigerant Recovery and Recharging . Leak test the system. Check the discharge temperature. Is the discharge temperature within specifications?	--	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 right side of the chart?	--	Go to the High Side Pressure	Go to the Low Side Pressure

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 the VDOT System Performance
2	Start the engine. Close all the vehicle doors and windows. Set the A/C control to 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 the VDOT System Performance
5	Repair or replace the cooling fan(s) as necessary. Refer to Engine Cooling Fan Replacement . 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.	--	Go to Step 8	Go to step 9
8	Recover and recharge the A/C system. Refer to Refrigerant Recovery and Recharging . Is the repair complete?	--	System OK	Go to the VDOT System Performance
9	Check for air in the A/C system. Is there air in the A/C system?	--	Go to Step 10	--
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 the VDOT System Performance
11	Recover the refrigerant. Refer to Refrigerant Recovery and Recharging . Repair the leak in the A/C system. Recharge the A/C system. Refer to Refrigerant Recovery and Recharging . 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 the VDOT System Performance

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

Are the high and low side pressures equal to the specified value?

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 equal to the specified value?

207 kPa (30 psi)

Go to Step 4

Inspect for the following conditions:

•	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. Refer to Air Conditioning Compressor Replacement .

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

Inspect the low side pressure.

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

2000-2800 rpm

Go to the Control Valve

Go to Step 5

Inspect the low side pressure.

Is the low side pressure within the specified values?

172-241 kPa (27-38 psi)

Go to Step 9

Go to the Control Valve

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

Is the liquid cold?

Go to Step 10

Go to Step 12

Inspect 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 the System Performance

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

Is the repair complete?

System OK

Go to the System Performance

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

Is the repair complete?

System OK

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

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

Is the repair complete?

System OK

Go to the System Performance

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 the System Performance
2	Connect high and low side pressure gages. Close all the vehicle doors and windows. Run the engine at 2000 rpm for 5 minutes. Set the A/C control to the MAX A/C mode. Set the temperature control to full cold. Set the blower motor speed on low. Is the low side pressure within the value(s) shown.	172-241 kPa (25-35 psi)	Go to the System Performance	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	Recharge the A/C system. Refer to Refrigerant Recovery and Recharging . Is the repair complete?	--	System OK	Go to the System Performance