My HVAC is defaulting to defrost under acceleration. It makes no difference if it is on heat or A/C. I did a search and it seems the issue is most likely a vacuum leak. So I'm wondering is there a common place where leaks occur or a line that is prone to going bad?

Thanks for any input. Oh and its a 97 4.6 xlt

 

Yes, check the little plastic hard lines behind the battery.

 

Thanks i will give that a try, I was under the impression the only ones back there were for the 4x4. Learn something new everyday. Ill check it out and see what i can find

 

Well, after a little poking, this is what i found,





The line deteriorated, probably from acid from the last battery. After i pulled the end out of the rubber connector i put a dab of super glue on the male end of the left over tube (so it would stay in since the barbed piece is now gone) and after a test drive no more cutting out heat or air!

Thanks a lot!