New to the forum...wondering if you guys could help me out.

I have a 93 6-speed with the automatic HVAC. My A/C will only blow out of the defroster and floor vents no matter what position the controls are set in (The green lights above the buttons turn on when the buttons are pushed). Every few days it will start to blow out of the dash vents for awhile, but it always goes back. Still blows cold though. Texas daily driver, 100k miles.

I'm thinking it is a vacuum issue. The check valve at the passenger side intake manifold works like it is supposed to, and I when i pulled it off i heard hissing, so the supply line to the HVAC vent controller isn't leaking. Just to check, I also hooked up a vacuum tester to this line, and it held vacuum.

I took off the cover under the steering column and contorted myself under there to take a look at the controller box where the vacuum lines go into it. I can't see anything wrong, but I think I need to take this thing out and inspect it; maybe the solenoids are not working, although i could hear clicking from the box each time I would change the A/C vent setting.

How do I get that stupid push-on nut off the vacuum line manifold so I can take the box out, or just to check for vacuum at the manifold?

Any other ideas? I really don't want to take the dash apart again (been there for heater core - what a pain)

Thanks,
Josh

 

Welcome.

Not sure if it's applicable to your '93, but I used the following to solve the same type of problem on my '96;
Link1
Link2

Good luck.

 

you will need a small screwdriver (1/8 inch blade) about 6 inches long and patience. you will have to work it off one side at a time. leave the box in place.

 

What RLG said. Even if you damage the push nut, it's no big deal, just replace it. Check the programmer circuit board for bad resistors or bad solders or any leaking vacuum hoses.

 

check your vacuum hose going to your vacuum ball. that was a problem on a car i had years ago. no matter what you had the fan settings on, it would blow top and bottom. not sure if your car is past relying on vacuum to open/close vent paths.

 

Thanks guys.

I finally got that controller box out of there and guess what... it had those rubber nipples that were collapsed (I thought only 96's had this problem...) I cut off the collapsed thin part and re-assembled and everything works perfectly.

 

great!!

I used the original hard plastic nipples out of my failed one (90) and put it in the replacement (96) that had the rubber nipples and it worked great.

 

Glad you got it fixed. Maybe a previous owner replaced the controller box with a new one post '96.

 

Not sure what I would have done without the info shown here. Mine had been driving me crazy for 2 years.

I ended up using the solution from "bvsmith" shown in "link 1". I recommend this over cutting down the connectors because those holes are still awfully small and may choke down the vacuum pressure too much. With new vacuum line you don't have to worry about that funky connector making a vacuum leak either. Plus I busted mine trying to get it apart because of the "push on nut" holding the 2 connectors together.

With the stupid connectors from GM now gone and reconnected with new vacuum line, it now works in about 1 second when switching from floor to vent or to defrost. Highly recommended mod for anyone with this problem. Took me about 5 or so hours total, but well worth it.

 

I had the same problem being unable to switch the ventilation control to the dash vents, but my problem was a little different. I bought my 92 and it already had this problem when I got it. It seems in the past a mouse took up residence in the car and chewed on the manifold for lack of the correct term where the three vacuum lines attach at the source of the engine vacuum line. That created enough of a vacuum leak to prevent switching of the ventilation to the dash. A bit of epoxy applied to this rodent created vacuum leak solved the problem. So lesson seems to be that you need to keep an open mind as to where the source of the vacuum leak might be at. Fortunately my ventilation system is now working as it should.