Vacuum Leak?

I posted this question some time back but lost the replies. Please forgive the duplicate request.

I have a '93 full-size Bronco. I have a problem with the dash vents. While accelerating and therefore depleting my vacuum reserve, my A/C defaults to blowing through the defrost vents. When I decelerate, the vacuum recovers and my A/C goes back to blowing as it should, through the dash vents.

Anyone have any advise as to where to look first for the leak. I've already replaced a small vacuum valve/device under the hood to no avail.

Thank you NES

Reply to
NES
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Having had the same problem with a couple of older vehicles, I'd check the vacuum canister first- one of mine had separated where the bracket was attached. Also check any of the plastic/nylon tee fittings- they have a tendency to get brittle and crack easily when they get older. You can also use a spray can of ether (starting fluid) or WD40 and spray sparingly along the suspected areas while the Bronco is running- your idle will increase when you hit a leak. Good luck! SC Tom

Reply to
SC Tom

You may not have a leak, but rather a bad one way valve. The valve is there to keep the low engine vacuum from pulling the vaccuum from the HVAC system. It's usually a small disk in-line, half white and half black (but not always that color).

Reply to
JimV

Thanks for the input. I was hoping it wouldn't come to that. LOL

NES

Reply to
NES

I've already replaced that device. But, thanks for the input.

NES

Reply to
NES

I'm not sure this will apply to you, but...

Have you checked the selector switch itself? If it's like I think it is, it'll be a vacuum switch that directs the vacuum to different vacuum motors. The switch is actually a valve I guess. It rotates as you push the selector across.

The reason I mention this is that I had the vacuum switch fail in a fan of mine a few years ago. IIRC, it's actually two plates of plastic that rotate against each other with a seal between. What happened to mine is that one of the plates cracked and the two plates separated slightly, releasing the vacuum pressure. When I went to the boneyard, I noticed that many of these had been removed already or that they were broken in the same place as mine. I ended up getting one from the dealer.

I know there are other vacuum leaks that are more likely the source of the problem, but don't overlook this possibility if you've ruled out others.

CJB

Reply to
CJB

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