I believe I'm chasing a vacuum leak, but don't know where exactly to look. While under load, my A/C vents in the dash default back to defroster mode. When I deccelerate, my A/C vents go back to normal (blowing straight out). I've checked the vacuum unit under the dash. It appears to be ok, in that it will hold vacuum. Also, after I've shut of the engine and the truck has set for awhile, the vents will have defaulted back to defrost.
My question is, is there a particular area or vacumm circuit I should focus on. I'm assuming the problem is more than likely under the hood. But, I could be wrong.
What you have is a bad accessory vacuum check valve.. I cannot to save my life recall exactly where it is on yours. They are relatively cheal.. Autozone or one of them may have a diagram with the location.
Look under the hood for a metal can about the size of a Tomato juice can, this is the vacuum reservoir, usually they rust out on the bottom side where the mounting bracket is crimped on. The vacuum reservoir has the check valve built in at the end where the lines attach.
I located and replaced the valve under the hood near the A/C evaporator housing. I'm not sure this fixed the problem as I'm still losing vacuum when I turn the motor off. I'll be driving this vehicle today. This will tell me for sure whether I've fixed the problem or not.
From: snipped-for-privacy@webtv.net Date: Fri, Aug 13, 2004, 7:58pm To: snipped-for-privacy@USA.NET (NES) Subject: Re: Vacuum leak? Hello I've been reading about your vacuum problem. The vacuum motor that controls the direction of air flow to the defrost/floor register is a
2-stage vacuum motor. No vacuum to _that_ motor or to the the whole control system, puts the system into 'default' mode, meaning only the defrost registers receive air-flow. It has 2 vacuum hoses attached and they come from your function control unit. The dash vents are controlled by another vacuum motor. When you select 'vent'/AC that motor closes a door-flap in the plenum system and channels air-flow thru the dash vents. So.....what is happening with your system is; upon deceleration that vent motor is loosing vacuum and since your function control is set to the vent/AC, neither is the 2-stage motor. I'd check that hose from the function control to the vent(panel door) vacuum motor. If Ford has kept the same color scheme for the vacuum hoses, the 2-stage motor has a Yellow and a Blue hose (or maybe a black hose with Yellow or Blue stripe) and the Panel door vacuum motor has a Red hose/Red striped black hose. Check the hose for a partial kink/bad connection/crack or some type of deterioration. A very handy tool to have is a small vacuum tester. A little tool called a Mighty-Vac has a lot of uses, isn't too expensive ($25 +/-). It's great for chasing vacuum leaks among other things. Most places that sell Automotive stuff is likely to carry it. It has a gauge on it and once the tester is hooked up and has pulled a vacuum, the gauge immediately tells you if the parts is bad or isn't holding a vacuum. The check-valve you replaced functions thusly; upon deceration, it closes off vaccum from the engine supply and then the vacuum system to your various vacuum controlled components relies solely on the vacuum reservoir 'can' in the engine compartment. The vacuum tester can check any of the vacuum components....handy thing to have. I think your problem is somewhere between the reservoir and the function control.....bad hose/connection most likely or a hole in the reservoir. Hope this is of some use to you......
(Since your email addy is invalid, I had to respond in this fashion)
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