Were you sent here from Symptoms?

Go to Step 2

Go to Symptoms

1. Start the engine.
2. Select the high blower speed.
3. Select the coldest temperature setting.
4. Select Bi Level mode.
5. Verify that the A/C switch is in the OFF position.
6. Select the recirculation mode.

Does the air flow from the selected HVAC ducts?

Go to Step 3

Go to Air Distribution System Description

Did the customer concern that the air temperature is normal at first, then changes during higher engine RPM?

Go to Step 7

Go to Step 4

With the engine running, take a vacuum reading at the manifold vacuum port.

Does engine vacuum exist?

Go to Step 6

Go to Step 5

Repair the no-vacuum condition.

Is the repair complete?

Go to Step 27

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Take a vacuum reading of the supply line at the vacuum control solenoids.

Is the vacuum reading the same as the engine vacuum?

Go to Step 11

Go to Step 8

1. Disconnect the vacuum supply line from the vacuum control solenoids.
2. With the vacuum gage connected to the vacuum supply line, start the engine, then turn the engine OFF.

Does the system lose vacuum after turning OFF the engine?

Go to Step 8

Go to Step 4

1. Inspect for leaking or collapsed vacuum lines between the engine manifold vacuum port and the vacuum reservoir tank.
2. Inspect for leaking or collapsed vacuum lines between the vacuum reservoir tank and the vacuum control solenoids.

Do the vacuum lines leak?

Go to Step 9

Go to Step 10

Repair or replace the collapsed or the leaking vacuum line.

Is the repair complete?

Go to Step 27

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Inspect the vacuum reservoir tank for leaks.

Does the vacuum reservoir leak?

Go to Step 23

Go to Step 11

1. Disconnect the vacuum line from the vacuum solenoid at the hot water bypass valve.
2. Apply an external vacuum source to the vacuum line.

Does the system hold a vacuum?

Go to Step 18

Go to Step 16

1. Disconnect the vacuum line from the recirculation actuator control solenoid.
2. Apply an external vacuum source to the vacuum line.

Does the system hold a vacuum?

Go to Step 18

Go to Step 17

Inspect for leaking or collapsed vacuum lines between the recirculation actuator and the recirculation actuator control solenoid.

Do the vacuum lines leak?

Go to Step 15

Go to Step 18

Inspect for leaking or collapsed vacuum lines between the heater water valve and the vacuum control solenoid.

Do the vacuum lines leak?

Go to Step 15

Go to Step 12

Repair or replace the collapsed or leaking vacuum line.

Is the repair complete?

Go to Step 27

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1. Disconnect the vacuum line from the heater water valve.
2. Apply an external vacuum source to the heater water valve.

Does the valve hold a vacuum?

Go to Step 14

Go to Step 26

1. Disconnect the vacuum line from the recirculation actuator.
2. Apply an external vacuum source to the recirculation actuator.

Does the actuator hold a vacuum?

Go to Step 13

Go to Step 22

1. Remove the passenger compartment air filter. Refer to Passenger Compartment Air Filter Replacement .
2. Inspect the recirculation door operation.

Does the recirculation door bind?

Go to Step 19

Go to Step 20

Repair the binding door.

Is the repair complete?

Go to Step 27

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Test the operation of the vacuum control solenoid to the recirculation actuator. Refer to DTC 28 Air Circ. Valve Voltage Low or Open CKT or DTC 29 Air Circulation Valve Voltage High .

Is the vacuum control assembly operating properly?

Go to Step 21

Go to Step 24

Test the operation of the hot water bypass control solenoid.

Is the control solenoid operating properly?

Go to Step 27

Go to Step 25

Replace the recirculation actuator. Refer to Air Inlet Actuator Replacement .

Is the replacement complete?

Go to Step 27

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Replace the vacuum reservoir tank. Refer to Vacuum Tank Replacement .

Is the replacement complete?

Go to Step 27

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Replace the recirculation vacuum control solenoid.

Is the replacement complete?

Go to Step 27

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Replace the hot water bypass control solenoid.

Is the replacement complete?

Go to Step 27

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Replace the hot water valve. Refer to Heater Water Valve Replacement .

Is the replacement complete?

Go to Step 27

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Cycle the HVAC controls in order to verify proper operation.

Did you correct the condition?

System OK

Go to Step 2