I have a 98 vette and my vent sw has stoped working. I can only get air from the forward vents. I don't have any electronic controls. Any one have any ideas on what is going on .

 

any faults? do you get temp control[hot/cold]?

 

Is this your problem: You cannot control from which vent the HVAC air is discharged? You press the various buttons, but the air flow does not come from a different vent, e.g., floor, face, defrost, etc?

If this is your problem, the vacuum lines which feed the "HVAC distribution manifold" are probably disconnected/damaged. If your battery area shows signs of the dreaded "leaking battery" syndrone, your lines were probably eaten away.

I fixed the problem by replacing the vacuum lines. PM me for what must be done.

HTH

 

Not, to thread jack, but my hvac won't do dual vents, like defrost and floor, or floor and front vents. It will stay on the previous one. My first battery leaked and I replaced it two years ago. I just noticed the problem recently. Is this similar?

 

SJ,

If you cannot control the vent output it is likely because of a vacuum line problem. The HVAC air distribution control system is vacuum operated. And the vacuum lines run directly under the battery and were apparently easily eaten away by the acid leaking from the bad battery side posts. The lines are 1/8" vinyl and get brittle, they do not remain pliable like other rubber tubing. I will post next how to find out if this is your problem,

HTH

 

To do the right thing for this post I have to get some diagrams copied from the Service Manual. So my post will be delayed...plus the sun just went below the yardarm and my wife has hoisted the happy hour pennant...priorities you know

 

If you cannot control the HVAC air flow from the various vents it may be due to several factors. My experience and this post is specifically to repair this problem if it is caused by broken vacuum lines. I had signs of battery leakage and could not control the air flow. I inspected the wiring harness beneath the battery tray and found both vacuum lines were eaten away. It was not easy to find those lines.

Steps to locate and splice the broken vacuum lines:
1. Disconnect and remove battery (negative terminal first).
2. Remove battery tray (figure 3).
3. Inspect the large wire harness bundles for signs of corrosion. If you are lucky you will find two 1/8" vinyl tubes somewhere inside the wire harness. There may be several wire harnesses to inspect.
4. Once you find them, trace them down to the vacuum tank (figure 1).
5. Splice in new 1/8" vinyl tubing. I got the tubing and splicers at Pep Boys. The tube that connects to the bottom of the valve connected to the bottom of the vacuum tank is the one going to the intake manifold and is the source of the vacuum for the system. The other tube coming from the side of that valve connects to the HVAC module solenoid in the instrument panel. You may have to remove the access cover in the passenger wheel well to get access to the vacuum tank.

NOTE: I never found the broken end of the vacuum line going to the intake manifold. That meant I had to splice a new piece of vinyl tubing from the valve under the vacuum tank directly to the fitting at the EXTREME rear of the intake manifold (figure 2). Moving the i/m is not too difficult, I have done it twice now and I can do it under an hour...and I'm not a mechanic.

PM me if I can help

 

Thanks I had the battery leak about two months ago and i cleaned it up and replaced it . I checked on it today and the new one was leaking and it did alot more damage this time. I going to spend a lot more time cleaning this time and I'm pretty sure the lines are damaged some where. What is the deal with this battery thing and what was GM thinking puting the ecm and all that wiring under the battery. I going to put a gel cell in it so this doesn't happen again. Thanks Again for all the help

 

My dash controls do not change from a bar going across it no letters or numbers, nothing. Have checked fuses all good. A/C runs with high fan and will not turn off. Also I have a code 15