AC not blowing through upper vents

ANYTHING TO DO WITH CHANGING THE AIR TEMP INSIDE YOUR VAN.

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Re: AC not blowing through upper vents

Post by 57BUDDii » Mon Jan 25, 2010 11:35 pm

I tried to upload the pictures of the "old factory" hose, but this is the message I received...

Sorry, the board attachment quota has been reached.

So, I will have to find an online photo hosting site to upload and link it to.
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Re: AC not blowing through upper vents

Post by crash » Sun Dec 12, 2010 12:19 am

the 3yr old post returns again .. LOL

I've not really bothered with the vent issues since it started again in the summer. as long as I had AC it didn't matter what vent it was coming out of :D

now that the cold weather has returned. My finds it hard to breathe it's so hot on her side, meanwhile, I'm freezing while driving.

NOW, pulled the dog house and ended up replacing the entire line from one vac canister in the engine bay to the one that scott posted the pic of below

Image

it was cracked in about 5 places in about an 8" section from the canister thing in the above pic

now that I have floor heat again, I got to noticing that the drivers side there's barely any coming out. while the pass side is blasting. there are 3 slices in the heaterbox that the heat comes out of on the pass side under the dash. for the life of me i couldn't find the driver vent under the dash for the feet. then.. after contorting into a painful U / L shape :rolleyes: .. there it was, one stinkin small outlet about 1" x 1.5" and it's more of a trickle of air than a blast on high, no wonder my feet freeze

i'm going to try to macgyver up some custom ducting to get more warm air on my side and blocked 2 of the 3 outlets on the pass side.

great design GM (not that they care) :yawinkle:
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Re: AC not blowing through upper vents

Post by timelessbeing » Sun Dec 12, 2010 12:54 am

The imbalance in amount of air bugs me too. Keep us posted.

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Re: AC not blowing through upper vents

Post by GnarliSafari » Sun Dec 12, 2010 3:54 pm

my van w was 2 years old when i first purchased it and the drivers side floor heat hardly worked then, my moms was brand new when she got hers and it was no better, as mentioned its a poor design from the start. i dont think the little vacuum line has anything to do with it. ive often contemplated using some duct tape on all the junctions behind the dog house to make the ducts a little more airtight, but then removing them would always be a pain. i used to keep foot warmers in my van for the winter months but oregon winters arent nearly as brutal as wisconsin and i have my van all tore apart at the moment and dont see putting it back together anytime soon so thankfully the heat in my truck works awesome!
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Re: AC not blowing through upper vents

Post by crash » Sun Dec 12, 2010 4:50 pm

great to hear it's not just me .. and I've always had cold feet. LOL

with this poor design it makes it even worse.

after some morning brainstorming, too much coffee and trying to be quiet in the house I've come up with a few things.

obviously, the blower motor/wheel is on the pass side. hence the much better flow/pressure on that side. even blocking off 2 of the 3 outlets on the pass side made a slight difference, it still wasn't enough. blocking off the heat duct that runs down the dog house and under the 2 front seats to give some heat to the rear isn't an option at this point, as it's my only source of getting any heat to the rear-ish section of the van since I either have a bad rear blower motor resistor, or I've disconnected it and don't recall (more possible)

the space under the dash as we all know is very tight, so here's my thought. if I can tap into the heater box on the passenger side and run one 'custom' duct at first to see how much it improves the drivers side. that would be a start. i was contemplating about what to actually run from the box and found myself eying my shop vac hose :-k after a quick search I found the standard price to be around $20 + tax for an standard 8' x 2 1/2"". being as frugal as I am, did a quick kijiji search and found someone selling a craftsman shop vac type accessory kit for $10 with an 11' x 1 7/8" .. a much better diameter for running under the dash and enough hose that I can half it and run 2 lengths if needed :D

going to pick up later today .. i'll keep y'all posted
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Re: AC not blowing through upper vents

Post by doyoulikeithere » Thu Mar 10, 2011 2:22 am

crash wrote: 8-[ i have really learned to miss the electronic/cable controlled 'everything' my dodge had and dislike the vacuum controlled everything these things have. ](*,)
WOW - The never ending thread about the biggest Peeve I have with these vans.

In fact I hate that vacuum system so much that from now on I will ONLY buy AstroSafari's built before 1990, cuz they used Pullcable controls.
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Re: AC not blowing through upper vents

Post by CaptSquid » Sun Jul 10, 2011 6:15 pm

After wading through this entire topic, it becomes apparent that those hard plastic vacuum lines under the dog house on my beastie have decided to break. What's the EASIEST way to find a vacuum leak? I've heard that spraying starting fluid in suspect areas will help. Is this so?
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Re: AC not blowing through upper vents

Post by litl_redhaired_girl » Wed Jul 13, 2011 7:54 am

Yes, you can find a leak that way- not sure if it will work for vents, tho. I just got through fixing all the lines in my '99 Astro. In the 103 degree heat. I am really crabby. It started with a leak in the radiator, and on the way to get coolant a brake line busted... Anyhoo, when we put humpty back together the vents didn't blow. I did replace a hose while the radiator shroud was off, so looked there first. The long (very) story short is I have replaced all but 8 inches of vacuum hose, and I took pictures of what I saw along the way. Here’s a link if it helps.
https://picasaweb.google.com/momlady77/ ... directlink
I took the pics 'cause I sure wish someone else had; I could have used them! In the end I went from NO air to AAHHHH.... \:D/
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Re: AC not blowing through upper vents

Post by timelessbeing » Sun Jul 01, 2012 7:27 am

So we all know that after a while, the vacuum lines decompose and start to leak, causing the notorious no upper vents problem. But another potential source of this problem is the vacuum check-valve.

Vacuum comes from the upper intake manifold, where air gets sucked into the engine to be combusted. Depending on engine load, and throttle position, the vacuum, or manifold absolute pressure (MAP), fluctuates. Consider these three situations:
  • At idle in park, the engine is drawing just enough air to stay running, but because your foot isn't on the gas, the closed throttle creates a restriction and you create low pressure (a vacuum).
  • When you're coasting down a hill in low gear, the engine is turning very fast and trying to guzzle a lot of air, but again the throttle is closed so you get very low pressure.
  • When you accelerate up a hill, the throttle is wide open (WOT), air can enter the engine as fast as is can burn it, and pressure is equalized. The intake manifold will be very close to atmospheric pressure.
So how can you operate your A/C when the engine is working hard, manifold pressure rises, and your vent controls are starved of vacuum? There are two things on the van to help with this. The first thing on the vacuum line from the engine is a check-valve, shaped like a 'T'. When manifold pressure rises enough, the valve shuts, thus maintaining a vacuum within the A/C system (one branch of the T) for you to use. This small amount of vacuum in the lines can be used up quickly, so there is an extra vacuum reservoir (the other branch of the T) for extended periods of WOT. You might have seen this black sphere mounted just inside the passenger side wheel well. This is why your vents will continue to work even after you've turn the ignition off.

So, to make a short story long, the check-valve can wear out too. When it does, it won't be able to hold a vacuum, and you'll notice your vents slowly stop blowing when you climb a hill or accelerate hard. The engine side of the valve is marked 'VAC', and air should only be able to flow towards it. That is how you can tell if it works. If you softly blow into the VAC side, you should feel resistance, but if any air gets through then it's no longer sealing.

Mine failed so I picked up another at the junkyard. Here they are side-by-side. From the outside, you can't even tell which one is broken. (left)
checkvalves.JPG
I decided to open it up to see how they work, how they fail, and hopefully prevent it from happening again. I was a expecting a spring loaded ball or mandrel against an orifice, but it was just a simple rubber flap. It wasn't very obvious how this one failed. I think the rubber simply fatigued and deformed (you can see the dimple in it). Nothing you can do about that. The buildup of black oxidized vacuum hose material probably doesn't help either.
checkvalveapart.JPG
Happy motoring. :cheers:

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Re: AC not blowing through upper vents

Post by bigjim » Sat May 25, 2013 11:32 pm

Searching for a clue about my divereter for the vents. I found this thread, looks like its been reserected several times and thanks to all who posted info for this fix... I found a really good you tube clip on the issue and thought i would share for future reference.... http://www.youtube.com/watch?v=muxXaQ_2 ... 2&index=18

I will get out soon and attempt this fix. Had a mechanic tell me it was the switch but I will try the vacuum lines first since the switch is just shy of 200 bucks.

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Re: AC not blowing through upper vents

Post by Herbie » Sun Mar 17, 2019 8:40 pm

I had had this issue for a little while, and I finally got around to fixing it this weekend. I'd been "building up to it" by making sure I had the main vacuum line (Part #15967970) and a spare check-valve/tee on-hand so that I could fix everything up in one pass. Turns out, I needn't have bothered, this round. After I finally got to really inspecting things, it was plain that the vacuum supply line from the manifold was still in good shape, but the short vacuum lines from the ball-reservoir and from the check valve to the nipple at the firewall were the ones that had failed. (Completely - they were crumbling as I touched them.)

Sadly, the plain 3/16" vacuum hose turned out to be hardest thing to find. I had to go to three local stores before I found anybody who had plain vacuum line in stock in any "close" size. (The Napa 20 minutes away finally had 5/32" hose, which I was able to make work.)

Image

So the moral of the story is this: If this issue is bothering you, give everything a close inspection first. You might find, as I did, that $2 worth of vacuum line is all you need to fix this. Took longer to jack and remove the passenger-side wheel (for easy access to the vacuum reservoir) than to do the rest of the repair.

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Re: AC not blowing through upper vents

Post by Bret Schmerker » Sat Sep 07, 2019 6:16 pm

:bounce: For those of you who need to re-plumb the HVAC controls side, I had the same problem my 1997 M11006 with those too-thin plastic lines - and upgraded the whole controls system to 3/16" fuel hose! Precaution against crankcase vapors, and I found reinforced rubber to hold up better in the long term than that plastic. Still makes one wish for steel tubing consistent with 1960's/1970's emissions rigging....
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Acquired Jul 2018 / Outfit in progress as of Nov 2018

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