First off, I have been searching for a while now about what the reason is that air only comes out of my destroster, regardless of the HVAC setting is. I know that it is most likely a vacuum leak. However, the question is (on a 3.1 v6) where does the main HVAC vac line come through the firewall (driver side? passenger side?) and where does it connect to?

BTW, I pulled out the HVAC controls and the pink line on the left is the only line that has vacuum which isn't all that strong to begin with. All other vac lines on the controls have no vacuum.

 

I experienced the problem you describe in my LG4--and I struggled to find a leak in vac lines and so forth to no avail. Finally, I replaced the the fingered switch (the one the various vac lines slip over) on the back of the HVAC. Problem solved. I "believe" that vac comes in on a single line and is directed/diverted to other lines by the selector switch on the HVAC face. By the way, the defroster is the default route.

JamesC

 

Nice! I hope this is the problem because I really don't feel like putting all this effort into it. Where can I go about getting one of those?

Just for my reference. Is the main HVAC vacuum line come out of a loom that the AIR pump switching valve does?

P.S. When I move the selector there is no hiss sound. Would you still suspect the selector?

 

The part I describe is still available from GM (less than $10 as I recall. That's probably the best solution. I had an extra HVAC around, so I just employed a used part).

Sorry, I'm not sure where the line comes from.

I didn't hear a leak either.

JamesC

 

Thanks alot. I'll try to get my hands on one of those. I'll let you know how it goes.

 

Note the following for 1990-91 cars:

Valve, Sel (W/C41) GM part # 16124558

Valve, Sel (W/C60) GM part # 16032395

GMpartsdirect costs: $13.45 and $8.10. Shipping and handling will probably be prohibitive, so check with your dealership.

JamesC

 

Just making sure, the part that we're talking about is black and connects the five different vacuum lines to the HVAC control?

 

Yep.

JamesC

 

Okay so today I went and picked up the part from GM and installed it. I eagerly switch the setting from off to vent and.......NOTHING! I had my hopes so high and was let down. Figures. But anyway, any other suggestions other than pinched or disconnected vacuum line?

BTW James, thanks for the help.

 

Is there any thing else that it could be?

 

Hum, well, I'm out of suggestions. You've probably already done a search and you've probably already seen this link, but you might follow it and pick up something useful.

https://www.thirdgen.org/techbb2/sho...hreadid=204268

JamesC

 

Actually the selector may have been bad after all. I now get air out of my vents....sometimes. If I leave the setting on vent at first it will only come out of the defroster but then after a while it will switch to vent. Then if I switch the setting from vent to defroster it switches right away and if I switch it back it takes a while again. Is there a reason for this delay? Is it normal?

 

The slowness sounds pretty normal. In my car, the shift from defroster to vent usually takes a moment or two. If there is no shift 'sometimes,' play with the selector lever a bit as it may be off a bit.

JamesC

 

Since my selector now actually works, despite the hesitation in switching modes, is it now safe to say that I don't have an HVAC vacuum leak? I've been driving around with my cd player out and the HVAC controls dangling for a while now. If I don't have a leak I would like to put them back in.

 

From all that you've descibed, I think you're good to go.

JamesC

 

I think I might be too. The vent and bi-level settings seem to be working, however, the heat setting still comes out of the defrosters, even after driving around for a while and the bottom bi-level (on the console) doesnt seem to have any air coming through.

 

Any ideas?

 

Can someone just tell me where the bi-level air and heater air is supposed to come out of? I wanna make sure everythings good before I put it all back together and have to take it apart again.

 

Bi-level comes out at the floor and out from the dash, the heater only comes out at the floor