Hey guys! I have a 97 Buick LeSabre, 3800 engine, with Climate Control problems. It seems to have a mind of it'* own! It will just randomly switch from A/C, vent, etc, to defroster. I have replaced the Climate Control dash box 3 times and it'* still doing it. What should I check next?

Let me guess: Never does it going downhill, but long gradual grade or steep grade and it will switch to defrost. Then, as things level out it gets back to the dash vents.

Right?

If so, vacuum leak somewhere.

Doesn't have to be in an incline. Nor do hard bumps seem to be the problem . Just switches whenever it feels like it.

Still likely a vacuum leak. Does it ever do it going downhill?

It doesn't matter road conditions. Uphill, downhill, straight, level, braking, accelerating. Just does it whenever it wants. No rhyme or reason.

Like Cathedral said, it has all the indications of a vac leak.....

The control head sends signals to the programmer, which in turn, activates solenoids to direct vacuum to the individual vacuum actuators...

What I would do, is drop the hush panel on the passenger side and the glove box(I believe there are two tabs at the top that release it and it folds right down).......you will see a vacuum manifold at the programmer....it has a violet colored line going into it(this is your vac source from the vac tank).....out of the manifold are 4 different colored lines, blue, white, green and orange, that go to the vac actuators.......with the car running, slightly move the lines out of the manifold listening for a hissing sound.......then grab that violet line and follow it back to the black line to make sure it'* not leaking at the joint....then check all the joints where the colored lines attach to the actuators, my moving them and listening for a hiss....

I have rarely seen problems with the programmer(the electrical part of it)......I have seen problems with vac into the programmer.....a black line comes from the vac tank and then it joins the violet line......you want to check your source.....disconnect the violet line from the black line and attach a vac gauge to the black line.....start car.....vac should build up to 18" right away......now shut car off....vac should hold on the gauge....if it immediately drops, you have a leak in a line, vac tank, or the check valve is not working(this is a usual problem when you open the throttle and then the vac is lost).......if vac holds, or very slowly drops, that is ok.....

The next culprit is the programmer itself....where the manifold attaches to the programmer.....the flexible manifold fits over plastic "nipples".....I have see these nipples break, and cause vac leaks.......sometimes they break, when a tech is testing the system with a manual vac pump.....he removes that 7-8mm nut, and then pulls on the manifold, which should just come off......but over time, one or more of the nipples stick to the inside of the manifold and break off when you pull.....so you techs out there, be wary of when you pull on the manifold, if it doesn't come off easy, beware.....those programmers are hard to find and expensive....

The other possibility, is an actuator that is leaking, and under the right circumstances, can cause havoc with the programmer.....

Thanks for the help and the link guys! I may have gotten it fixed yesterday but not really sure how. Followed the directions in the link, didn't find any obvious leaks, but the darn thing has been working correctly since I got my hands in there and checked the connections. Did something right but don't know what, lol! Again, thanks!

Now you know what to do next time it acts up, thanks for letting us know how it came out!

My 97 Olds 88 had a similar problem. It was slow to change from the default of defrost to the vents. When I started having problems with my fuel trims being out of whack(identified with a scanner) I looked into a vacuum leak. I found my vacuum line going to my HVAC unit had crumbled into a worthless piece of garbage. I replaced the piece of hose with a vacuum line purchased from AutoZone. As these cars age rubber gets more brittle. A foot long piece of vacuum hose from a parts store is cheap insurance. The size that I used was referred to as windshield washer hose.

Careful using windshield washer hose for vacuum hose, sometimes vacuum will cause the hose to collapse or kink in corners where it looks fine with the engine off. If it'* the stuff with the thick walls then it'* usually fine though.