Climate control air diverter

Welcome to 2CarPros.

Rich, if it is an aluminum line, that most likely isn't a vacuum line. If you upload a pic of it, I can confirm it for you.

Now, we have a couple different links related to vacuum issues. Is this the one you checked?

https://www.2carpros.com/articles/air-vents-stay-in-the-defrost-position

Now, if there are no leaks, then we have to suspect what is called a Mode Door actuator has failed or isn't receiving vacuum to change air flow direction. I am going to provide the directions for the mode door actuator replacement. Rather than just replacing the part, I recommend checking to see if there is vacuum going to it. At the bottom, I will attach pictures of the component that correlate with the directions. They will indicate where the vacuum supply is located (hose). Simply check if you can feel a vacuum to that hose when trying to change the air flow direction. Note that the engine must be running when you to it.

If there is vacuum, then follow the directions for replacement. If there isn't, then you will need to trace the vacuum hose back to the controller to see if you can find a leak there or you can remove the supply line direct from the engine to see if there is vacuum there.

Now, there could be two different designs used on this vehicle. If you have automatic temperature control, the mode door actuator will be electric. That is the first picture below. If it isn't automatic, then it will be vacuum.

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1998 Jeep Truck Grand Cherokee 4WD L6-4.0L VIN S
Mode Door Actuator Replacement
Vehicle Heating and Air Conditioning Air Door Actuator / Motor Service and Repair Procedures Mode Door Actuator Replacement
MODE DOOR ACTUATOR REPLACEMENT
REMOVAL

WARNING: ON VEHICLES EQUIPPED WITH AIR-BAGS, REFER TO AIRBAGS SYSTEMS BEFORE ATTEMPTING ANY STEERING WHEEL, STEERING COLUMN, OR INSTRUMENT PANEL COMPONENT DIAGNOSIS OR SERVICE. FAILURE TO TAKE THE PROPER PRECAUTIONS COULD RESULT IN ACCIDENTAL AIR-BAG DEPLOYMENT AND POSSIBLE PERSONAL INJURY.

The mode door actuators for vehicles equipped with the standard equipment manual temperature control system are vacuum controlled. The optional Automatic Temperature Control (ATC) system uses electric motors to actuate the mode doors. The temperature/blend-air door for all models is actuated by an electric motor. The service procedures for both types of actuators are covered by the following procedures.

Heat/Defrost - Panel/Defrost Door Motor
This motor is used only on models equipped with the optional Automatic Temperature Control (ATC) system.
1. Disconnect and isolate the battery negative cable.
2. Remove the two bolts that secure the center instrument panel support bracket to the left side of the floor panel transmission tunnel.
3. Remove the two bolts that secure the center instrument panel support bracket to the instrument panel.
4. Remove the center instrument panel support bracket from the vehicle.

Heat/Defrost - Panel/Defrost Door Motor Remove/Install

pic 1

5. Unplug the wire harness connector from the heat/defrost - panel/defrost door motor.
6. Remove the three screws that secure the heat / defrost - panel/defrost door motor to the bottom of the heater-A/C housing.
7. Remove the heat/defrost - panel/defrost door motor from the heater-A/C housing.
8. Reverse the removal procedures to install. Tighten the mounting screws to 2.2 N.m (20 in. lbs.).

Heat/Defrost Door Vacuum Actuator
This actuator is used only on models equipped with the standard manual temperature control system.
1. Remove the heater-A/C housing from the vehicle. See Heater-A/C Housing for the procedures.
2. Turn the heater-A/C housing upside down on a work bench.

Heat/Defrost Door Vacuum Actuator Remove/Install

Pic 2

3. Unplug the vacuum harness connector from the heat/defrost door vacuum actuator.
4. Disengage the heat/defrost door pivot connection from the heat/defrost door pivot pin.
5. Remove the screws that secure the heat/defrost door vacuum actuator to the heater-A/C housing.
6. Remove the heat/defrost door vacuum actuator from the heater-A/C housing.
7. Reverse the removal procedures to install. Tighten the mounting screws to 2.2 N.m (20 in. lbs.).

Panel/Defrost Door Vacuum Actuator
This actuator is used only on models equipped with the standard manual temperature control system.
1. Remove the heater-A/C housing from the vehicle. See Heater-A/C Housing for the procedures.

Panel/Defrost Door Vacuum Actuator Remove/Install

pic 3

2. Unplug the vacuum harness connector from the heat/defrost door vacuum actuator.
3. Disengage the panel/defrost door pivot connection from the panel/defrost door pivot pin.
4. Remove the screws that secure the panel/defrost door vacuum actuator to the heater-A/C housing.
5. Remove the panel/defrost door vacuum actuator from the heater-A/C housing.
6. Reverse the removal procedures to install. Tighten the mounting screws to 2.2 N.m (20 in. lbs.).

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Note in pic 2 I highlighted the component in question and circled the linkage. Make sure the linkage didn't come disconnected.

Let me know if this helps or if you have other questions.

Take care,
Joe

Welcome back:

You are very welcome. Let me know what you find.

Take care,
Joe