97 JGC Heat/Air goes to defrost w/o moving switch

[lewispb00]

I have a 97 JGC that no matter what direction you have your heat going, when you push the gas it goes to defrost. When you let off the gas the air goes back to the floor or whever you have it set. My 92 Chevy Lumina does the same thing. Is this a vacuum problem? Whatever it is, is it relatively easy to fix or something I would have to take to a mechanic?

[Bob D.]

It's usually a vacuum problem. Check the under hood vacuum lines for leaks.

[taxman9]

Try searching this forum for 'vaccuum' you can usually find a previous post on the topic you're looking for. Sounds like a leak or you need to install the check valve that needed to be added to most GC's.

Take a much harder look at your vaccuum hoses all over. I dealt with this during the heat this summer and found where a line going in through my firewall had been rubbing and finally developed a leak. The minute I had it patched the vents were working again. I patched it quick by using the crevice tool from WD/40 or PB Blaster inside to bridge the line but later a small piece of fuel line for a RC engine did a perfect patch over the break. Too dark now to get a pic maybe I can get one tomorrow.

And you're not gonna believe the check valve, I mean checking your oil is probably harder than putting in a new one.

http://www.twocanines.biz/images/vacuum_line_repair.jpg

http://www.twocanines.biz/images/check_valve.jpg
Tough to photograph, orient the valve so that vacuum is allowed into the engine block.

[legalfee]

There's a TSB out on this here: http://home.sc.rr.com/janet/TSB/24-01-96A.htm

On Jeeps always check for a TSB first. SJ