I know that hvac issues have been discussed a gazillion times, and still comes up, as blend door and vacuum issues seem to be endless.

I have been battling issues with my 96 hvac system for several months, and think i have some partial success, notably the blend door. I managed to reshape, grind and reconfigure a Dorman Actuator, and get it to fit, and the blend door will move from hot to cold, as demanded by the C68 automatic climate control.

I removed the Programmer, trimmed the rubber nipples, and eliminated the connector by installing 5 pcs. of rubber vacuum line to each colored hard plastic vacuum line. This worked fine for a few days, then reverted to intermittently blowing out the defrost, then deteriorated until it will only blow out the defrost and floor.

The two hard plastic vacuum lines from the valve at the intake manifold and then disappear into the wiring harness, I understand go to the cruise control and the HVAC Programmer.....Correct? Which is which?? I attach a piece of rubber vacuum line to each one, and can blow or suck on one, but the other is solid.

Tried a vacuum hand pump on the tan and blue lines going to vacuum actuators and neither will hold vacuum ?? I think the tan one goes to the defrost actuator, and is in the default position, allowing air to blow out the defrost vent and floor.

I believe that the orange line goes to the recirc and outside air actuator.

Does anyone have a diagram of the HVAC vacuum lines that they could share with me ?? Think I saw one somewhere, and the black plastic line (source) and orange line intersect on HVAC housing ??

I no longer seem to have source vacuum to the programmer, could it have anything to do with the orange and black lines together ?? Any input will be greatly appreciated. These things ain't easy to work on

 

Appears you have a leak some where from the vacuum check valve to the HVAC Programmer.

With the HVAC Control head off and engine running there should be no vacuum to any of the actuators.

 

ok, thanks. Believe I figgered it out. Ran a vacuum line directly to the programmer from the intake, and everything seems to work, and switch instantly. Also, seems to idle better. So gotta bypass something, "McGyver" something from the intake to the programmer, may "t" into the cruise line and just run one from the 2-way valve at the intake ??

 

I'm having similar trouble with my HVAC, I been meaning to dig out this programmer everyone keeps talking about. IIRC it's located above the gas pedal on the drivers side?

Might you have any photos to share of the location? What the controller looks like and or the portions that were visually damaged?

 

The original poster has a problem which is specific to a 96 Corvette.

Here's an excellent thread describing the problem and fix.

https://www.corvetteforum.com/forums...l-problem.html

Here's a video describing the C68 system.


If you don't have a 96 and the air flow is coming from the wrong vents the problem is usually the vacuum check valve or the vacuum hose going to the check valve is bad. The check valve is located under the plastic passenger side fuel rail cover.

The check valve looks like this.


The 96 HVAC Programmer used soft plastic where the vacuum hoses connected. The hose nipples would collapse when vacuum was applied.

The Programmer is a black plastic box.

Looks like this.


Here's a picture from the service manual of its location which is above and to the right of the gas pedal mounted to the fire wall by one bolt.

The Programmer has one electrical connector.
The Black vacuum hose is the vacuum source.
The other vacuum hoses are color coded as shown in the picture below and go to the vacuum operated actuators.

 

Oh that was just a super juicy post! Thanks! Gobbled that input up like Johnny 5!

 

Have had similar problems on my previous z31 nissan 300zx cars. Purchased a 90 c4 Auto with 44k miles. Same problem as mentioned thruout the thread... I'm 68 and 6 ' 2" , guess I'll have to learn the corvette yoga also... Loving

my new first vette though...