Need Explanation Of How Air Vents Work

[PaulRV6]

I am trying to figure out why the vents sometimes work and sometimes don't. Same with the A/C coming out of the vents.

If I put a vac source on the plastic line along the firewall that goes into dash is it suppose to hold vac? I figure this must control the door openings/closing correct?
I checked the vac accumulator and it holds vac. I thought if I could put a source of vac on that line I could see if the doors would open to the vent.

Not sure how this all works? Please help.

paul

 

[BuickBrick]

I just went through this with my 87.
Yes that line to dash should hold vacuum.
With controls turned off there should be no leak.
If it holds vacuum then try each setting to track down the leak.
On mine the vacuum select valve was bad. It is located on the back of the controls. It has about 9 different colored vacuum lines
going to it. Also there is a second vacuunm select valve for heat.
To remove - pull front bezel -- remove the 4 screws --
then unplug 2 wiring harness -- then remove jam-on nut to cable on bottom -- then remove 2 jam-on nuts on vacuum port and pull off. Once out you can easily test vacuum port. If I remember right the Purple line is the main feed.

 

[PaulRV6]

Buickbrick, so what if it does not hold vac with switches in off position?
Are you saying the way to get to the controls is thru the front and not the back? I was going to pull off the under panel to get to the back but if not I will work thru the front, is that correct?

paul

 

[BuickBrick]

I had my stereo out at the time.
You can try to reach up from the bottom but it is probably
easier in the long run to just pull the control assy from the front.
It only has 4 screws + what is attached. 10 -15 minutes.
Once out you will see where the 9 vacuum lines connected to a
vacuum control valve. The vavle consists of two halves sandwiching a rubber gasket held together by a white "button" (not sure of the proper name). The white button gets old and breaks its tabs. You can replace the control or do what I did and drill a hole and put a screw through the middle of the white piece.
Note : the white piece does not move.
Here is a link to the part #.
http://www.turbobuick.com/forums/showthread.php?s=&threadid=89465

 

[salvageV6]

Paul, the service manual has all the vaccum diagrams in it for each lever position and how the doors move and work.

Worth the $75 from Helm Inc.

Anyway do a search on vents or air conditioning and I have described the lever postions and which hoses should have vacuum on them for a few postions.

If you need more just ask.

I'd check the hoses for leaks first and the mode doors for sticking.

 

[PaulRV6]

PROBLEM SOLVED!!

Well BuickBrick you were right on. It was the white button. Once I got the controls pulled out far enough I could see the white button loose and not holding the round black piece tight against the white piece (very technical).
You mentioned a rubber gasket between the white/black halves, mine did not have one, only plastic against plastic. It works know after I squeezed the the white button in tight but I could see the hook broken off.
If anyone else has a problem with vents not working, check white button on vac manifold in back of temp settings controller.

I will either try your trick of putting in a screw or go buy a new one. What did the screw go into since there is a hole thru the white piece?

This board is and the help is awesome. Thanks again!!!!

paul

 

[BuickBrick]

Let me clarify about the rubber gasket.
It is between the two halves of the valve. It has little valleys engraved in it for the different settings. The white piece has a spring washer on it for tension. I broke the -- tips (hooks) of the tabs off so they no longer protrude out past the control to hold it together. I then drilled a hole through the center of the white piece and threaded a screw with washer to hold it all together. I used a fine thread screw (probably metric) and tightened till the spring washer deflected and the control was not too tight to turn.
Hope that makes sense
The valve is only about $18 but I did mine this way because the dealer parts house was closed.