SouthernSon

I suppose I need to access the bottom of the dash above the accelerator pedal to find vacuum line. Anyone know of an easy way to do this? Remove seat? :confused:

ham

I've been told that this happens when the system has a problem. I have the same issue and haven't found my problem yet. Sure is a bummer in the summer when the sun goes down, it fogs up the outside of the lower part of the windshield and I can't see where I'm going unless I use the wipers.

SouthernSon

Ham, I noticed on this last trip that if I do the following, it sometimes works: shut off air a couple of minutes before killiing motor, wait a couple of minutes after start up before engaging air and then let the engine idle for a couple of minutes. The vents will then distribute as desired. I suppose the vacuum is strongest at idle. Also, sometimes you can hear the flap close with a good slap! But, if you jump in, hit the air and drive off, you only have top and bottom. I just came back from Cape Kennedy and the moisture in Fl. was all over the windshield. I used the wipers when I could not get the vents right. :mad I'll update when cure is complete.

Blue260

There is a "T" fitting under the passenger side fuel rail covers. This controls the vacuum operation of the vents. Since it lays on the intake manifold it is prone to melting. It looks like a little tiny fuel filter- only black and plastic. This may be your problem before you start ripping apart your dash.
Hope this helps,
chris

KMO

Blue260 is right on. I had this problem with my 95. This valve was totally melted leaving the vacuum lines floating. I couldn't find any reference to it in the service manual and the parts counter guy was clueless. Luckily I asked the vette mechanic at the dealer and he went and got it from stock for me. It's called a valve P/N 14056648. I kept the paperwork cause I'm sure this is gonna happen again. Hope this solves your problem.

White 1995 Coupe

ZR_Don

I had the same problem with my T fitting as KMO and Blue260. Another forum member suggested to check this out. Cost was $5.95 from GM.
Stay Cool!

Dualnic

This is the part...the other members are talking about it is located under the right fuel injector cover...check this first....all around.

04Z16

I have the same problem but the tee fitting is not burnt or cracked. I pulled the lines off put a vacum pump on them and the one that comes out to the side held 30". The one straight out the back I had to pump it up about 50 times before it would get above 20". When I reconnected the lines and pulled the vacum on the front of the check valve I was able to pump it to about 25" and then it bled off to about 5" and stayed there. My question is:
Where does the vacum line come into the passenger compartment at? I have the electronic A/C controls and before I tear apart the dash I wanted to chase the vacum end down and maybe see if it is the cannister or actuator under the dash. Any help would be :cool:
Leo

Corvette ED

Dualnic,

The GM part number for that valve is 14056648 and every dealer stocks them. They must also fit other GM products.

GiDvEtTe84

I had this problem. After much headache trying to find vaccum leaks, i bought a new heater/AC control unit. Solved my problem.

Lst-rd-c4

I had this problem with my 96. Does your cruise control work? If it does it is not vacuum related. On mine, the accuator door stuck inside the plenum. The dash had to be removed to get the plenum out to fix. The dealer charged 8 hrs. labor to do this :eek:

Geoff13IOM6GS

I'm interested to see if there are any more ideas. Mine isn't stuck but it takes about 15 seconds for the air to come out the correct vents........

SunCr

The 15 second delay is normal and is considered the purge mode. The idea is to direct the air to the heater outlets to prevent fogging. It can be overridden by switching from auto to manual control.

CG77VETTE

Does anyone know if there is a similar tee-connection on an early '86 and if so is it located in the same place?

SunCr

Check between the distributor and the rear of the plenum on the driver's side or follow cruise vacuum to tee fitting, then follow line towards distributor and rear of plenum.

SouthernSon

I appreciate all of the replies, and especially the picture, Dualnic, but alas, after replacing the little vacuum part and new hose parts I still have the problem. I suppose the next stop will be under the dash to see if hose has a kink in it. :confused:

Corvette ED

Southern Son,

The 96 Shop Manual has a good diagnosis on this problem. It shows you what to do if the cruise works and the vents don't. It goes through a step by step check and you should be able to solve your problem.

JTsTOY

My 96 was also doing this when I bought it. I replaced the GM T with a regular vacuum T- problem solved. (Thanks MR DAVE!) Also when I done the throttle body bypass I had to move another air valve? that ties into the vacuum T that I replaced, wound up putting the hoses on wrong and presto- problem returned. Swapped the hoses around, working fine now.

FrankLT4

As a direct reply to your question: the 96 service manual says to remove the
LH trim cover (which I believe means the carpeted piece and the steel panel that your knees contact in a crash. Both come off easily.) My 96 has the same problem. I found a vacuum line that comes thru the firewall close to where the clutch pedal contacts the floor while depressed. My vacuum line shows damage from the clutch pedal contacting it. I'm not sure that that is the problem since I quit at that time last night. It may not even be the right vacuum line, but I sure hope it is and I sure hope it leaks. You don't have to remove the driver's seat to do the above, but I am considering doing so so I can lay on my back and look up at the layout rather than continuing to bend my body in an unnatural way to work under the IP.
As a more detailed response to you and other posts the 96 service manual is fairly detailed, see especially pages: 1C-3 for info on doing the diagnostics on the HVAC control head (you use the up and down fan buttons), 1B-15 for HVAC Systems Diagnostics flow chart, and 8A-68-3 for the Tech 1 diagnostics (must be a dealer tool, uses the body systems cartridge and must be programmed for 1990 rather than 1996 !!)
One of the early checks is to check for manifold vacuum at the vacuum tank. Then check for vacuum at the black line at the HVAC control head. Later checks involve removing the IP so vacuum can be checked at the vacuum actuators, and the Tech 1 check which involves jumping a wire from #4 HVAC control head to # 14 on the DLC. I am writing this from memory, so read the service manual before doing the work. I am not able to write every step and my memory and understanding is far from perfect.
From what I have learned so far many 1996s had this problem. See Hutch's Wild Thing site for Grand Sports. Most of the time the problem seems to be a bad HVAC controller. Sometimes it is wet insulation in the duct work that blocks the valve that diverts the air. And sometimes it is a vacuum line problem at the right side of the intake manifold. From what I read in the service manual I disagree with the post that said if the cruise works that it is not a vacuum problem. I believe that even if your cruise works you still need to do vacuum checks before proceeding to electrical checks.
With so many 96s having this problem does anyone know if there is a service bulletin, free fix from GM, or help from Bowling Green Action Center???
Whoever finds the cause of this problem on their car please post the response so the rest of us might save some time and money. Thanks FranKLT4

FrankLT4

An update to my last post: The black line you are looking for is about 8 to 10 inches above the accelerator pedal. The other line I found the day before by the clutch pedal has nothing to do with the HVAC system. Once you remove both the carpeted trim and the metal stamping under the gage cluster you will easily see the black (vacuum source) plastic tube connecting to the HVAC programmer along with the blue, pink, tan, and orange plastic tubes that run to the various ducts. It is very difficult to work with these tubes especially if you have big hands. I was able to test on of my lines and found it had manifold vacuum present. Also I connected a hand held vacuum pump to the nipple that the pink (center vent) tube connects to. I put 25 in. of vacuum on this connection and did not hear my vent open. Also with the engine running and AC on and vacuum applied by the hand held pump the vent did not blow cold air. So I am beginning to become convinced that my vent valve may be stuck. (MY carpeting was also wet.) Now the problem is how to get at the valve?? Tear out the IP?? or just the radio? Anyone know. (This is sure not a job for a typical home mechanic such as myself.)