Air From Vents Drops Off
 

I couldn't find anything matching my problem in a search, so hopefully someone has heard of this.

1996 E-350 7.5l. When the AC is running, it works fine for a while but the air from the vents trickles to almost nothing after a while. Happens on regular and recirc mode, also from any vent position I select. The fan blows the same, but the air just stops coming out. When I put my hand to the vent I can feel only a tiny flow of air and it is cold.I can shut the system off for a while and it will repeat. Anyone have this happen before?

See if this is what you are having happen.

https://www.ford-trucks.com/forums/1...efrosters.html

Lucas

Let me edit this response to say that while the behavior of my system seems to differ from the behavior mentioned in that link, it is a VERY nice bit of information and I am going to go into the inner fender anyway, because after 23 years there's a good chance my vacuum line is deteriorated and will need attention anyway. Thanks very much for that useful link indeed.

But the air does not seem to divert, rather is just stops. I can't feel it coming out anywhere although I can hear the blower motor as normal. I'm wondering if the AC system is freezing up and ice is blocking flow?

You don't need to hack up any sheet metal to achieve a work around for the failed vacuum reservoir. I'm not overly familiar with the E-Series before 1997 but if the '96's are similar you simply need to relocate the reservoir inside the cabin---I tucked mine up under the passenger side dash, close to the bottom of where the air bag should/might be. Adding the factory check valve as per the schematic completes this operation and you've saved your sheet metal.

You just need to find the vacuum source line from the intake where its joined to another line leading to the vacuum reservoir which is located UNDER the evaporator case---I show the exact location in a thread here entitled "Finally Found It!" or something to that effect. By routing the vacuum from the intake to the inside the cabin you eliminate an unnecessary source of aggravation. I've done this on two of my own E-Series so its not that difficult.

Given a bit of time I could post Ford part numbers which total under $30 and a few photos of my own installation. If you're in a bigger hurry proceed as you will---I understand.

HTH

Thanks JWA. I'm not in a major hurry, no. A few recent threads reminded me that I've been meaning to try to figure this out but it's not a 911 deal at the moment. I appreciate your reply.

I'm not really convinced that linked thread is my issue; it just looked like a good idea to do the work to eliminate that eventual possibility. What do you think about what I describe as the issue I'm seeing?

Warren I'm not sure what your condition or observation might be---I'd have to be there when this happens to get a better handle on it. I would think if the blower motor output suddenly became restricted there would be a noticeable difference in its sound. You're saying it doesn't seem to change which suggests air is still being moved but not through the ducts.

I'd remove the access cover top center of the dash and watch the vacuum motors move as you change the Function Control knob between Heat, Vent, A/C, Max A/C etc etc. You might see something there.

I'd also feel around the lower dash board to see if the air flow isn't somehow directed away from the ducts.

Sorry I can't be more helpful than this. :(

Thanks. I took a drive in it this morning (it's hot today too) hoping to really get a good feel for the exact operation, since this vacuum thought will not leave my head. Unfortunately, and of course, it did not divert/fade in the time I was out. That figures.

If that vacuum tree in the dash is the culprit, is it going to be something clear to see, like a disconnected or split line, or are there diagnostic steps to follow?

Ive had this happen before.

I had very similar symptoms to what you describe, AC barely moving through the vents, what I didn't realize at the time was that it was coming out of the defrost with a little more flow than the vents were producing. Fairly quick easy and painless to disconnect the vacuum line under the hood that serves the heat/AC system. if you buy 15' of vacuum hose you can reach from there to the 'vacuum hub' under the access panel on top of the dash. If memory serves you disconnect the black line and connect your hose to that port on the 'hub', I routed it out of the corner of the hood and through the passenger's window to do this test. If that brings your air flow back out of the vents you can narrow things down a bit more and if you have to do the workaround you have enough hose to do it.

Always the way it is huh? :)

Okay so I owe you a few photos anyway so I'll get to that this morning--promise. I'll show the various vacuum servos in their proper orientation when the Function Control is calling for different conditions. That should be more helpful.

Back later-----stay tuned! :)

https://cimg2.ibsrv.net/gimg/www.for...e642ce55dc.jpg
If memory serves (always questionable! hehe) I edited this diagram to match the colors of hose I found under that access panel on top of the dash (up where it's really hot on a sunny day!) maybe this helps...

Thanks! And thanks to everyone so far for your inputs. Appreciate it!

Your edited color-added schematic is good---thanks for taking that time! :-X22 (Reps sent.)

Warren I have a number of photos showing the proper orientation of the vacuum servos relative to the dash-mounted Function Control switch (Heat, Vent, A/C, Defrost etc); also have the recirculating door shown both open and closed, also relative to the Function Control switch. Which or what can I post that'll be most helpful to you?

Well, I've never been one to say "Hey, that's just too much helpful info, please stop!!" So feel free to post up anything you wish. Thank you sir.

:) Yeah "too much information" is a bit of a misstatement right? :)

I'll put something together in a "how to" of sorts about the entire vacuum controlled air flow directional changing system. If I were a better photographer this would have already been done so I'm still sorting, editing and adding captions to what I have already.

If something specific comes to mind you're welcome to PM me or post here---I'll subscribe to this thread.