geminiman82

Hey everyone,

I am obviously new around here, but I have been lurking for a bit. I have a 98 and recently after having the trans repaired (the battery was disconnected) I had to retrain the Actuators for the A/C due to the vents on the d/s blowing hot while the p/s blew cold. I got this issue taken care of but I am now having another issue.

No matter what I do I cannot get the vent on the top of the dash (the defrost vent) to shut off. Even if I swith the HVAC Controls to floor only, it still comes through the Defrost vent as well.

Any ideas?? Thanks for the help in advance.

lucky131969

Any codes? You may have a broken or chaffed vacuum line under the battery tray. Pull the battery and the tray. There are two vacuum lines that reside underneath that become brittle and chaff on the wire bundle. Physically run your fingers over the lines to inspect for condition. If you find a break or wear spot, you can cut out the affected area, and repair with 5/32 vacuum tubing.

Bill Curlee

All the HVAC damper doors are vacuum controled. Your missing the vacuum signal to that hvac head unit. It starts on the back of the intake manifold goes thru the main wiring harness to the pass fender well under the battery and thru the fire wall to the havac unit.



BC

geminiman82

Thanks guys, I will look into this as soon as I am not at work. And because I forgot to put it in my original post (which I can't believe I forgot)....there were no error codes. In fact this is the first time in a LONG while that I haven't even seen a Historical code come up.

Thanks again.

slyq757

Soooo, have you had a chance to look at it? Im having the same issue! I found/repaired one of the vacuum lines under the battery but that didnt fix the issue. I also didnt find a second line.......

dcj

You will find all of the answers you need in this post:

http://forums.corvetteforum.com/c5-t...nge-vents.html

Trace the vacuum lines from behind the intake manifold, through the harness, under the battery, and to the vacuum canister (located in the passenger side wheel well behind the fender). Also trace the line going in through the firewall underneath the battery.

Don't be surprised if you find SEVERAL vacuum leaks. I fixed one leak in the line from the manifold only to find 2 more coming off the canister going into the firewall. I also discovered a crack in the checkvalve at the cannister.

I've heard some say that most of the vacuum line damage under the battery is from corrosion created by faulty OEM batteries that had a tendency to leak. I did find corrosion under my battery and cleaned, primed, and painted the area. Always best to swap out for a gel based battery (Optima, etc.)

AC is good and cold now with at least an 80% improvement. The air also goes where the 5 position control dictates. The interior vacuum valves that operate the system are large and easily heard when operating properly. No sound = no vacuum...