1998 Tahoe 4DR 4WD LT interior air flow control issue

[jonnycakes]

My 1998 Chevy Tahoe is having problems controlling the direction for the air flow inside the cabin. I can control temp and blower speed with no problem. I am unable to change the air flow from vent, feet, and defrost positions. Once in a while I will hear an air door kick open or closed. I am pretty sure this is a vacuum line problem as I can hear a vacuum sound from behind the dash at slow speeds when I roll out of the throttle. Is there a diagram out there showing the vacuuum lines and where they run? I would like to review a diagram or some type of how to instructions before I start ripping the dash which is a pain. Is there a step by step process someone has made up so I can diagnose and fix the problem? Any help would be greatly appreciated.

 

[SunlitComet]

There is no vacuum line used. The electronic servo motor that controls those functions is located above and to the right of gas pedal. Check the white wire on it for varying voltage as move the control knob. If the signal does not change then the control head is probably at fault. Remove the servo and observe the motor as you move the knob as well to see if the motor reacts. The door opening or closing maybe be the recirc door running on auto because of combination of mode and temp settings. As for the hissing sound that may just be refrigerant or water flow sounds.

 

[MoroneSaxatilis]

There is no vacuum line used. The electronic servo motor that controls those functions is located above and to the right of gas pedal. Check the white wire on it for varying voltage as move the control knob. If the signal does not change then the control head is probably at fault. Remove the servo and observe the motor as you move the knob as well to see if the motor reacts. The door opening or closing maybe be the recirc door running on auto because of combination of mode and temp settings. As for the hissing sound that may just be refrigerant or water flow sounds.

You, sir, are amazing. I've been on here a few weeks and have learned more about my Yukon from your posts alone than from any other source.

 

[jonnycakes]

There is no vacuum line used. The electronic servo motor that controls those functions is located above and to the right of gas pedal. Check the white wire on it for varying voltage as move the control knob. If the signal does not change then the control head is probably at fault. Remove the servo and observe the motor as you move the knob as well to see if the motor reacts. The door opening or closing maybe be the recirc door running on auto because of combination of mode and temp settings. As for the hissing sound that may just be refrigerant or water flow sounds.

I went ahead and replaced the servo motor(blend door actuator) next to the gas pedal. This did not change anything once I replaced the actuator motor. This motor controls the lower duct door for air flow to the feet position. I inspected and removed the duct that directs air flow to my feet and to the back seat position. I can see the air duct door opens and closes when I turn the air flow control knob so I know the servo actuator is working. But what I did notice is what looks like some type of metal air flow door just hanging right above the lower door. The metal air flow door is completely coved in sticky rubber substance. It looks like one side broke but its hard to see. I tried to tear it out but one side is still attached. Now Im not sure but I would think this metal door should be attached somewhere up above the lower duct work. I think this might be my problem and I am wondering what this air flow door is and how to fix it. Will I have to replace the whole air box?

 

[SunlitComet]

IIRC that door works in sync with the first to direct the air up top. Unfortunately I have no actual pictures of interior of the box and that might become hard to come by. Perhaps you can identify the part using the link below. Are you sure the external linkage are in place and not broken?

http://www.genmotorinfo.com/Picture...96+CK,A/C+&+Heater+Module+ASM,(C60)+-+TC09045

 

[jonnycakes]

IIRC that door works in sync with the first to direct the air up top. Unfortunately I have no actual pictures of interior of the box and that might become hard to come by. Perhaps you can identify the part using the link below. Are you sure the external linkage are in place and not broken?

http://www.genmotorinfo.com/Picture...96+CK,A/C+&+Heater+Module+ASM,(C60)+-+TC09045

Thanks a bunch for the link. When looking at the diagram the part labeled number 26 is the door I see hanging right above the lower door. I checked into these doors and Dorman products actually has door kits so I can replace all the door inside the air box. When I mentioned that this door was covered in a black tar like substance I figured out that the manufacture places foam around the edge on both sides of the door which I think is to help seal the door better. Well over time heat melted the foam along with the adhesive to make a sticky mess. This probably caused the door to get stuck in one position and when I tried to adjust the air flow the door would not move and probably broke one of the linkages. Looking again at the diagram I see two linkages numbers 29 and 28. These linkages connect to another box number 30. I assume this box is what forces air out the windows defrost vents. This makes total sense since 90% of the air always flow out the window defrost vents. So I guess the next course of action is to figure out how to remove the air box so I can get inside. Wish me luck and if you have any ideas I'll take em. Thanks again!!!!!

 

[SunlitComet]

this procedure should cover everything to get the housing out:


Evaporator Core Replacement REMOVAL PROCEDURE

CAUTION: Refer to Battery Disconnect Caution in Cautions and Notices.

1. Disconnect the negative battery cable.
2. Drain the engine coolant. Refer to Draining and Filling Cooling System
3. Recover the refrigerant. Refer to Refrigerant Recovery and Recharging
4. Remove the instrument panel.
5. Disconnect the electrical connectors, as necessary.
6. Remove the floor air outlet.
7. On diesel engines only, remove the powertrain control module.
8. Remove the hinge pillar trim panels.
9. Remove the blower motor cover.
10. Remove the blower motor (5).
11. Remove the steering column.
12. Tilt back the instrument panel assembly. Refer to Mode Actuator Replacement .
13. Remove the coolant recovery reservoir.
14. Disconnect the heater hoses.
15. Disconnect the evaporator tube.
16. Remove the accumulator.

1. Remove the screws (1,4).
2. Remove the nut (2).

1. Remove the screw (2).
2. Remove the module assembly (2). Ask an assistant for help in removing the module assembly, if necessary.
3. Remove the seven screws in order to remove the cover plate (8) on the bottom of the evaporator case from the module assembly.
4. Remove the heater core and the seal from the module assembly.
5. Remove the tour screws in order to remove the case cover (6) of the evaporator from the module assembly.
6. Remove the evaporator core.

INSTALLATION PROCEDURE

1. Install the evaporator core. If the evaporator core is being replaced, add oil. Refrigerant Recovery and Recharging
2. Install the four screws that hold the case cover (6) of the evaporator to the module assembly.
3. Install the heater core and the seal into the module assembly.
4. Install the seven screws that hold the cover plate (8) on the bottom of the evaporator case to the module assembly.
5. Install the module assembly (2). Ask an assistant for help in installing the module assembly, if necessary.
6. Install the screw (1).

1. Install the nut (2).
2. Install the screws (1, 4). NOTE : Refer to Fastener Notice in Cautions and Notices.
3. Tighten the following fasteners: Tighten

• • Tighten the module mounting screw to 11 N.m (97 lb in) .
  • Tighten the nut (2) to 2.8 N.m (25 lb in) .
  • Tighten the screws (1,4) to 1.9 N.m (17 lb in) .

1. Install the accumulator.
2. Connect the evaporator tube.
3. Connect the heater hoses.
4. Install the coolant recovery reservoir.
5. Install the instrument panel.
6. Install the steering column.

1. Install the blower motor (5).
2. Install the blower motor cover.
3. Install the hinge pillar trim panels.
4. Install the powertrain control module and the mounting tray.
5. Install the floor air outlet.
6. Connect the electrical connectors, as necessary.
7. Add the engine coolant.
8. Connect the negative battery cable.
9. Charge the system. See: Refrigerant\Service and Repair
10. Inspect the system for leaks. See: Testing and Inspection\Component Tests and General Diagnostics

---------- Post added at 02:28 PM ---------- Previous post was at 02:26 PM ----------

Also the link below is for mine but the parts should be identical if you need stuff from dealer.

http://www.gmpartsgiant.com/Page_Pr...icture=False&ddlSm=4WD&minorIndexID=TC0904501