my truck hasa vaccum problem and i think it under the dash? what it is doing, say you have the defroster on and you start climbing a hill or down shifting where you raise the rpm quickly the defroster will shut off and blow on the floor. I know it a vaccum leak but i dont know where to look, i am just gussing that is under the dash.The truck idles great and does everything else right just does that. Even when you have the a/c on blowing at your face it will shut off and go to defrost, it is all screwed up.

if anyone has any advice or has this happen to them help is needed

thanks

 

I would say bad check valves first. If not, then the lines would be next. I'd bank on the valve though. I have a CTD, but you should still have a large check valve at the brake booster if you have vacuum brakes, and then one more check valve along the smaller line that cruises across the top of the firewall. Your vacuum line for the defrost should pass thru the firewall somewhere around the area where the coolant lines pass thru to the heater core.


Both check valves are inexpensive and the first thing to replace.


Good luck with your ride.