Has anyone had where their ac would not change from the defrost mode to the dash mode, anyone know how to check out this system on a 1996 LT1

Thank You

 

You either have a bad control head in the dash or the mode door actuator is bad. The actuator will be attached to the evaporator case in the center of the dash and might be a real ***** to get to. Older cars worked on vacuum, 90's models went to an actuator to open and close blend door and mode doors. [8D]

 

hey LB,

Thanks for the info, do you have a site that I might view where these valves are located, i like to see a visual
blowup of the dash and is there a way to test the easier of the 2 solutions.

Thanks for your help, it's driving me crazy

 

I don't know of one, but someone might. Some of the actuators are a major pain to get to. I'll have to research it a little more.

 

These do operate partially off of vacuum. The first thing i would check is the 2 way vacuum check valve under your passenger side fuel rail cover. It has three rubber lines connecting to it, one coming out of the intake, one going to your a/c head unit, and one going to your cruise control. These are very prone to failure due to the intense heat. IF, that proved to be what's wrong, you can pick one up for $5 or less at any decent parts store.

 

I agree there is a vacuum problem. If vacuum doesnt get to the controller, the system stays in defrost by default. I believe its a safety thing. The HVAC Programmer (automatic / type C68 HVAC) is located above the gas petal. You have to take off lower dash trim under steer col and knee bolster under that, for access. Then you have to contort yourself up under the dash with a light to find the 6 colored tubes plugged into the upper right corner of the programmer black box. The black colored tube is vacuum input. If you can pull it out, you can check if vacuum is getting to that point. If it is, then the programmer box is screwed up. Do the LEDs flash in the controls when you turn on the car? If so, this means a HVAC fault. I can tell you how to dump the codes from it and what site to find the codes.

Good luck.
Greg G
96 LT1 yellow

 

Had the same problem with my 95.
Replaced the vacuume valve as Soonerman suggested and I now have AC blowing in my face again.
My cruise control is probably working again too!
Now if I could only get that stupid PKE received module working my baby will be like new..
GOOD ADVISE SOONERMAN!