Vacuum Controller: Testing and Inspection

Fig.26 Adjust Vacuum Test Bleed Valve - Typical:

Heater A/C Vacuum System Diagnosis:

VACUUM CONTROL SYSTEM
Use an adjustable vacuum test set (Special Tool C-3707-B) and a suitable vacuum pump to test the heater-A/C vacuum control system. With a finger placed over the end of the vacuum test hose probe, adjust the bleed valve on the test set gauge to obtain a vacuum of exactly 27 kPa (8 in. Hg.). Release and block the end of the probe several times to verify that the vacuum reading returns to the exact 27 kPa (8 in. Hg.) setting. Otherwise, a false reading will be obtained during testing.

One-way Check Valve
1. Disconnect the heater-A/C vacuum supply (Black) tube in the engine compartment. This tube passes through an opening in the dash panel.
2. Remove the one-way vacuum check valve. The valve is located on the (Black) vacuum supply hose at the brake power booster.
3. Connect the test set vacuum Supply hose to the heater side of the valve. When connected to this side of the check valve, no vacuum should pass and the test set gauge should return to the 27 kPa (8 in. Hg.) setting. If OK, go to step Step4. If not OK, replace the faulty valve.
4. Connect the test set vacuum supply hose to the engine vacuum side of the valve. When connected to this side of the check valve, vacuum should flow through the valve without restriction. If not OK, replace the faulty valve.

Heater-A/C Controls
The operation of the recirculation air door can be viewed by removing the blower motor and looking up into the heater-A/C unit housing inlet. Refer to Blower Motor for the proper service procedures.
1. Connect the test set vacuum probe to the heater-A/C vacuum supply (Black) hose in the engine compartment. Position the test set gauge so that it can be viewed from the passenger compartment.
2. Start with the Mode control in the Panel position and the Airflow control in the Outside position.
3. Move the Airflow control to the Recirculation position (the recirculation air door should move to the inside-air position). After a short pause move the Mode control to the Defrost position (the recirculation air door should move to the outside-air position). The test gauge should return to the calibrated setting of 27 kPa (8 in. Hg.) after each selection is made. If the gauge cannot achieve the calibrated setting, the vacuum circuit or a component has a leak.
4. If the gauge achieves the calibrated setting but the recirculation air door does not move, there is either a pinched vacuum line or a failed actuator.

Locating Vacuum Leaks
1. Connect the test vacuum probe to the vehicles (Black) supply hose. Position the vacuum test gauge so it can be viewed from the passenger compartment.
2. Place the Mode control in the Panel position and the Airflow control in the Recirculation position.
3. Remove the instrument panel center bezel.
4. Remove the center air outlet duct.
5. Remove and block the supply (Black) vacuum line at the heater-A/C control. The test gauge should return to the calibrated setting of 27 kPa (8 in. Hg). If not, there is a leak in the supply line.
6. If there is no leak in the supply line, reconnect it to the heater-A/C control and remove the actuator feed (Red) line from the heater-A/C control. Block the vacuum connection on the heater-A/C control from where the line was removed. The test gauge should return to the calibrated setting of 27 kPa (8 in. Hg.). If not, there is a leak in the heater-A/C control.
7. If there is no leak in the supply line or the heater-A/C control, reconnect the actuator feed (Red) line to the heater-A/C control. Remove and block the actuator feed (Red) line at the actuator. The actuator vacuum port is accessible behind and above the glove box. The test gauge should return to the calibrate a setting of 27 kPa (8 in. Hg.). If not there is a leak in the actuator feed line.
8. If there is no leak in the supply line, the heater-A/C control, or the actuator feed line, the leak must be in the actuator itself. Connect the vacuum hose from the Vacuum Test Gauge directly to the actuator to verify the leak.

Locating Pinched Vacuum Lines
The operation of the recirculation air door can be viewed by removing the blower motor and looking up into the heater-A/C unit housing inlet. Refer to Blower Motor for service procedures.
1. Connect the test vacuum probe to the heater-A/C vacuum supply (Black) line. Position the vacuum test gauge so it can be viewed from the passenger compartment.
2. Place the Mode control in the Panel position and the Airflow control in the Recirculation position.
3. Remove the instrument panel center bezel.
4. Remove the center air outlet duct.
5. Remove the vacuum supply (Black) line at the heater-A/C control. The test gauge should drop indicating free flow through the supply line. If not, there is a blockage in the supply line.
6. If there is no blockage in the supply line, reconnect it to the heater-A/C control. Remove the actuator feed (Red) line from the heater-A/C control. The test gauge should drop indicating free flow through the supply line and heater-A/C control. If not the vacuum switches in the heater-A/C control are not functioning.
7. If there is no blockage in the supply line or the heater-A/C control, reconnect the actuator feed (Red) line to the heater-A/C control. Remove the actuator feed (Red) line at the actuator. The actuator vacuum port is accessible behind and above the glove box. The test gauge should drop indicating free flow through the supply line, heater-A/C control, and the actuator feed line. If not, there is a blockage in the actuator feed line.
8. If there is no blockage in the supply line, heater-A/C control, or the actuator feed line, the actuator must have failed. Connect the vacuum hose from the Vacuum Test Gauge directly to the actuator to verify whether the actuator has failed.