Air output goes from dash vents to floor when accelerating

[BT5150]

I did search around on this and I'm guessing its a vacuum leak somewhere but I just thought I'd ask before I start tearing stuff apart because I didn't see anyone else with the exact same problem. The good news is MY AC DOES WORK!!!! WOO HOO!!! I bought the van last Dec from a lady who's brother owned it before he died, so she didn't know if it worked or not. The van has been awesome so far and now that we just got an early warm snap here in WI (almost 80 the last couple days!) I was able to test out the AC and yes, IT WORKS!!!!

Anyway, here's what mine does: When I accelerate any more than moderately, with the vent selector set anywhere from "vent" to either of the AC settings that blow through the dash, the air output will shift and start blowing out of the floor vents, to the point where there's almost no air coming out of the dash vents. Then, as I let off of the gas, the air will start blowing out of the dash vents again. I've seen other posts where people talk about losing most of their air output all together, but I didn't see anyone with this exact problem. I'm guessing its also a vacuum leak somewhere, but thought I'd check here first.

[Jasen]

Theres a plastic vac hose that runs from the rear drivers side to this 3 way The loose rotted line goes down to the vac can which you can access through the right wheel well. The plastic line gets cooked and breaks and it doesn't take much more then looking at it to break it. I was able to leave some plastic hose on the connection fittings and replaced the rest with rubber vac line.

[BT5150]

I was just looking for that 3 way part you mentioned and then I noticed this tube that looks like it should be attached to something somewhere, but its just sitting there-is this a vacuum line?

[Jasen]

I don't know about that one. Looks like the one that goes to the back of the motor, but it's at the wrong end of the motor bay. Did you find the 3 way, it should be in the same area, behind the aluminum A/C thingamajigger there. Can't ever remember what that parts name is
The one your showing might go to the vacuum can. Mine was a rubber line, but that doesn't mean GM or someone else didn't change things.

[Corsemoto]

Here's the breakdown for a 2004, your's may be slightly different but I doubt it.

The vacuum line elbow you found is most likely #12 (vacuum hose passenger side end, the other end attaches further back in the engine bay on the driver's side) and you need to find #11 (control valve heater/ac) to reattach. It's where Jasen said, look to the left and behind the engine oil and transmission dipsticks, you may see it there.

[trapper20]

Jasen, I think it's an accumulator.

[chevymaher]

That hose in question looks like it went to the water control valve for the heater hoses.
You can get a vacuum control valve from the dealer for ungodly amounts of money. It allows vacuum to travel one way and shuts in the opposite direction.
I use a aquarium bubbler check valve for a air pump. Buck eighty at a aquarium place. My first one lasted 10 years. Just replaced it last summer. They the same size as the vacuum line. Just replace defective original one. They have a handy arrow on them. Direction of travel is toward the engine.

[Jasen]

Now that Corsemoto points it out, I went out and looked at mine. That line looks like the vacuum feed line that runs from the back of the motor, it hooks to the 3 way part #11. I'd bend it a bit and see if it breaks, this is the line I first mentioned about getting brittle and breaking. GM routed right over the top of the intake manifold. I re routed mine away from the hot zone when I replaced it with rubber. At the fittings (in your pic) the plastic was ok, so I cut out the bad plastic and just slipped new rubber vac line over them.

[Corsemoto]

I just replaced the one in my van, broke when I moved it out of the way of the thermostat housing. The dealer didn't stock but Advance Auto has it AC Delco #15-30578 for like $8

http://shop.advanceautoparts.com/webapp/wcs/stores/servlet/product_Hose-Heater-and-A-C-ACDelco_18056577-P_1220_R%7CGRPEMISAMS

http://www.amazon.com/ACDelco-15-30578-Source-Hose/dp/B0016IY3QW

[Lumpy]

I hate those hard plastic vacuum lines. I broke one yesterday (that had broken before) while I was removing my battery. Got some generic line and rubber boots today. But I'll replace as much of it as possible with rubber fuel hose. I like fuel hose better than that soft rubber stuff sold as vacuum line. The more sturdy fuel rated, reinforced hose doesn't crack and split and get brittle like the other stuff does. About a dollar per foot is cheap.


Lump

[BT5150]

Ya, that definitely looks like this part in my pics, but I just can't figure out what the heck it should be attached to. It comes out of a bundle of wires, looks like its coming from the driver's side, but I can't figure out what it should plug into and I can't find that 3-way piece people are talking about. There's not a lot of slack in the line, so whatever it would attach to would have to be within several inches of where it sits now. I'm puzzled. I did try sealing it up with some tape, just to stop it from sucking air and that seemed to help the AC problem, but I still don't know where that those should go.

[Jasen]

Maybe this will help. If the one line and the line coming from the firewall came off, the 3way could have fallen down below. You'll probably have to pull the tire and the mud skirt to get in there and look. You'll see the vent canister ball just above the frame towards the front.

[steverod]

hi my name is steve,i have 1998 astro van with the same problem, when i step on the gas i lose my a/c from the vent to the front defrost, ive had the vents probles before and ive channged the small vacumm line,many times,and problem solved but this time its diferent when i let off the gas the vent start blowing again and my trasmission when im cousting it changes diferent, i still think is a vacuum problem but dont know what to do next, if anybody can give any advise it will graetly appreaciated Thanks.

[DonD]

I had the same issue. Replaced the lines from ball to joint and joint to firewall. This line* had also become unplugged from the heater control valve very near the vac ball...tight quarters but I got it plugged back in.

*

[footprintsinconc]

i am sure that end that is not connected should plug into part number 20 in the parts picture above. when i was fixing my intake leak, i found it unplugged too. take your time and get in there to see that, its not easily visible. the elbow fits over a bump on the bottom of the water control valve. the ball does not have that bump, it accepts a normal hose end only, while the water control valve does not accept a normal hose end, only that 90 degree part will fit over it.

the other thing you want to make sure is the hose that is linked in amazon or the advance auto parts site will probably need replacing....its hard plastic that goes back over time and my have cracked some where you will not notice easily...just replace for $10 (part number 12 in the above diagram).

lastly, i would change the hose from part number 11 to the ball and from the firewall to the part number 11....that do deteriote over time and it will only cost you like $0.15 per foot to replace...

this should take care of your vacuum lines that are in the engine compartment and should fix your issue.

i can take some pics tomorrow if you want and post it for you.