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How to fix No Air from Vent / Vacuum / Intermittent AC Issue

147K views 292 replies 149 participants last post by  AstroWill 
#1 · (Edited by Moderator)
I have been having the "defrost only" or "No air flow through my vents" / "Intermittent AC" problem and have been researching all over for a solution. A lot of posts have pointed to the problem and alluded to the solution but the question which like most persons I have been asking is how do I fix it. So I just fixed the issue on my 2000 Safari and I thought I would document the solution.


Tools Needed:

- stubby (2 inch) flat head screw driver or socket/ratchet handle

- a friend with a small hand

- bright enough work light

- 2 beers if you are alone, and 2 for each friend who decides to help. (You will need these).


Parts Needed

GM Part Number - 15967970

I bought the part for CDN $10.90 in Edmonton, Alberta

Here is a picture of the part


Here is the GM Tear down for this part. The one you are interested in is #12 .


Step 1 - Identify that this is your problem part.

Find the vacuum and trace it. If its not obviously broken, trace it to the end and look for cracks on it. It runs from behind the the silver AC tank and on the right of the heater core on the passenger side under the hood. Mine looked fine at first, but as I traced my hand over, about half way down it just disintegrated. Click on any of the following thumbnails for a more detailed pic.





Step 2 - Remove essential parts in the path

If you have determined that this part is bad, removed the air cleaner box and the hose going to the intake manifold. There is a metal piece to which the intake rubber hose connects, you can move it too. It will give you about 1 additional inch of work room (every inch counts! trust me). I didnt move this metal but in retrospect it prolly would have saved me 20 minutes or so.




Step 3 - Remove the old connection from the back of the engine

This part can be tough, and if you have long skinny arms, or if you have a friend with this tenet, then you are in luck! This end is on a little valve on the back of the engine about even with the gas pedal on the driver's side. In case your existing vacuum line broke off and you are not sure where to look, just take a good look at what the end should look like as per the first pic in this post, then look at the pic below for the routing. In a dark skinny hole (hence the need for the bright worklight) on the back of the engine you will see two valves.. one points up and just above that is another which points frontwards and slightly left . The latter is the one you want. You will probably only be able use your index and middle finger. Pull hard on the connector and it will come off. When you get it off, have a beer on me!



Step 4 - Putting it back together again

Be strongly advised... Start by connecting one end of the new vacuum hose to the connector described in step 3 . You want the upper side free because if you have arms like mine, then you wont be able to see in the dungeon properly as your hand will be in the way. So place one end of the vacuum hose between your index and middle fingers on the right hand, take a good look at where the connecting valve in, then lean forward and try to reconnect it. This is the hardest part.. but dont give up. You may even be tempted to go pull the doghouse.. this will not help! When it snaps on, force it on, remove your hand and verify. If its not on completely, go ahead and force it on. When its all done, have the second beer on me. So when this end is properly connected, I suggest routing the other end above the radiator hose, and above the intake manifold, and then to the T-connector at the top. Then reassemble your intake manifold and air cleaner box.


Without taking off the doghouse cover, project should take about 30 - 45 minutes.


Now, go enjoy the whiff of air from your vents as if your truck was still new.
 
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#178 ·
This thread has been an amazing resource.

After changing the serpentine belt yesterday, I suddenly had no air blowing through the dash vent. After quickly finding this thread, I saw that I had indeed snapped the hose-probably when I removed the air handler.

This morning I picked up part #15967970 at the dealer for $10.58, and the dash vents blow perfectly now. It was a tight fit for my hands. My wife's were definitely better suited for the task. Lifting the air intake was a help. And most importantly for me, no need to go through the doghouse.

Thanks, everyone!
 
#179 ·
PROBLEM SOLVED (Where after I replaced hoses above, now compressor didn't come on at all):
In short, the connector to the High Pressure Switch (plugs into the back of the compressor) must've been on last legs; I guess I pulled it out a bit when swapping hoses.

After trying 97Cargocrawler's good hints & others, checking everything in the front I could think of with no luck, I unbolted the doghouse & pulled it back a foot or so, didn't fully remove the doghouse. I then looked at the High Pressure Cutoff switch connector, which plugs into the back of the compressor. The connector was nearly apart & fell to pieces as I tried to shove it back on. (NOTE: To pull off the connector, first pull the little blue sliding tab toward back of van and DON'T LOSE IT; it likes to hold on, then fly).

I put a paper clip across the pins, compressor worked. Replacement connector was $35 from dealer, and didn't include the blue sliding tab. Snip, strip wires, use the crimp wire connectors, and plug it in, you're done (except for putting doghouse back on).

THANKS EVERYONE, this thread & others on the site helped get the Astro chilling in time for summer.
 
#180 ·
Cool beans. I have the same issue on my new '00; the shop who did the LIM for the guy broke the connector. No pieces remained. I have to steal the locking tab off my '99 (thanks for the tip on removal) but I already had the new replacement piece here.
 
#181 ·
Hey Guys,
Could use a little help here.

OK based on the GM diagram supplied on the first page. I bought item #11 the Vacuum valve, #12 the vacuum line from the valve to the back of the motor, and the hose lines #34.
I replaced the vacuum valve first, about two weeks ago. Didn't do the trick. Ordered the vacuum line, got it, installed it AND replaced the 5/32 hoses at the same time. The vacuum line that I ordered seemed to look in good shape, but could it be defective? I wouldn't think so simply because it's a very simple item.

The system would work a little, when doing a soft acceleration, but now it doesn't blow from the front dash vents at all! Else is there to the same issue?

Thanks for any help guys,
~Junior
 
#183 ·
Another A/S site success---I almost took out the resevoirs to get to the vacuum ball, found out here about going thru the wheel well. So easy, i didn't even bother taking the wheel off, just turned it as far as it would go and had plenty of room-finally great A/C just in time for 90 degree weather! replaced 2 lines, one was broken off and the other was rotten-Thanks A/Sdot com!
 
#184 ·
I had to replace three sections of vacuum hose/tubing to get mine working.

1) The semi-hard plastic tubing that runs from the intake manifold to a tee fitting mounted on the black plastic AC box. I had to remove to dog house to get to the intake manifold end. The other end is easy to see and get to just by opening the hood. This requires maybe 36" of tubing.

2) The 5/32" vacuum hose running from the tee fitting to another hose that goes through the firewall into the AC unit on the inside of the van. (that is where it goes, but you do all the work in the engine compartment under the hood) this requires only about 10" of new hose.

3) The 5/32" vacuum hose going from the tee to the vacuum reservoir ball. About 24" of new hose used.

The "tee" I refer to is more than just a tee. It looks like it is a one way check valve.
 
#186 ·
IMG_4090.JPG
IMG_4088.JPG
I am new to this forum, but wanted to provide some ideas about this notoriously troublesome vacuum line. My shade tree mechanic had "fixed" this issue by simply taking the broken hard vacuum line, and "repairing"it by attaching flexible/rubber vacuum line between the broken ends. This worked fine for a while, but the real issue is that the old hard plastic vacuum line is still brittle, and due to all the engine heat, will eventually break again. So below is my recent method to permanantly fixt this with a new vacuum line, that is "reinforced" with1/4" split loom plastic tubing, wrapped in reflective HVAC tape-- to deflect some of the engine heat. Here are some pictures.

IMG_4089.JPG


IMG_4094.JPG


IMG_4095.JPG
 
#188 ·
I had rodent problem with my donor van as I am taking out sub frame assembly I noticed vacuum line chewed through. probably tree rat. teeth marks on remainder of hose. the damage was done at vacuum reservoir bulb I can see the difficulty with all the stuff crammed in the front. easiest is with engine out of van. My arms are small but still looks like a job for little armed people. (or let some one else do the job)
 
#189 ·
I've had two problems with this on a 2001 Safari cargo van.

The first problem was where the vacuum hose comes over the block near the exhaust ports. You can only access it by removing the dog house. The hose had melted clean through from the heat. I kept the right-angled ends, cut them with plenty to spare, and spliced in a piece of line from Lordco using rubber cement. The replacement piece was just big enough to fit over the stock hose snugly.

Some of the old hose had become brittle from the heat but there was enough in good condition to make a good splice.

I made sure the new line was routed away from heat by strapping it with tie wraps to hoses that felt cool.

The second problem struck while I was on a trip and I had to suffer no AC control till I got home. Quite by accident, I pulled on an AC hose under the hood where the hoses come together and it came free. It had been hanging down in the vicinity of the passenger side suspension.

I crawled under the van after running the front passenger side tire up on the sidewalk and found where the hose attaches. It's hard to explain, and I have no idea what it does. Anyway, there was a nipple that was apparently for a small hose and I pushed the vacuum hose onto it.

Problem solved.
 
#190 ·
The vacuum hoses under the hood are the only ones exposed to high heat, outdoor weather conditions and dirt. So they are the ones most likely to fail. What they do is pretty simple. They supply vacuum to the interior A/C systems, which is used to actuate air flow control flaps. There are three hoses involved under the hood. The first hose, which is small semi-rigid hard plastic, goes between the intake manifold and a check valve. This hose is the "source" of the vacuum. On the other side of the check valve are two softer flexible neoprene hoses. One goes through the firewall to the A/C system where the vacuum is used, and the other goes to a spherical vacuum reservoir. The reservoir stores vacuum, to keep the flaps in position when vacuum at the intake manifold is low. The check valve keeps air from the intake manifold from back flowing into the vacuum reservoir and A/C system when the manifold pressure is positive (low or negative vacuum) compared to the reservoir pressure. If your A/C performance seems to change depending on engine RPM, that is a sign that the vacuum reservoir hose is leaking or disconnected.
 
#191 ·
Thanks to the original poster and for all the comments in this thread. I had the same problem on my 2000 GMC Safari, replaced the small diameter supply vacuum hose, and the problem was fixed. On mine, it was broken right at the intake manifold. I opened up the doghouse and it was very easy to change out the hose from there. I didn't need to disconnect the airbox at all, and passed the other end of the hose over the air intake pipe by taping the other end to a stick.

I could only find this hose at the dealership, autoparts suppliers do not carry the part here in Canada. While at the dealership, I also bought the check valve that forms the "T" junction that hangs next to the A/C compressor. Wondering if I should replace this too, although I'm worried I'll break the other hoses while doing so...

I got the job done just in time before a deep freeze and big dump of snow!
 
#193 ·
I'm working on a '92 van, and found that my part #12 is in tact.

My question is if I apply vacuum (with a hand pump) to any of these lines, are any of them supposed to hold vacuum? I can pump really fast on part #12 and get the lever on the vacuum module to come up some, but not stay up.

I'm not exactly sure how this system works, as it's my first time working on AC.

There may be a possibility that something's disconnected/broken on the controls itself, but I'm not sure how to remove it to check.
 
#194 ·
WoodButcher said:
Odds are good other bits will be brittle too. Buy 10 feet of rubber vac line from your local auto parts before you bother with the check valve. Replace all the lines you can get to.
x4centillion :handgestures-thumbupleft:
 
#195 ·
Dimitri13 said:
I'm working on a '92 van, and found that my part #12 is in tact.

My question is if I apply vacuum (with a hand pump) to any of these lines, are any of them supposed to hold vacuum? I can pump really fast on part #12 and get the lever on the vacuum module to come up some, but not stay up.

I'm not exactly sure how this system works, as it's my first time working on AC.

There may be a possibility that something's disconnected/broken on the controls itself, but I'm not sure how to remove it to check.
Here's a potentially dumb question.

The engine needs to be running to operate the vents, correct?
 
#198 ·
I just finished fixing 6 Astro van vacuum issues and learned a lot of tricks.
FIRST: DOT use the Dorman adapters nor the standard tiny tubing. Get tubing that fits over the AC one way valve by the fan, buy 2 mechanical "Old school" clamps. ALL the dorman and GM parts use the same plastiser in manufacture. The products harden and crack, first with a loss of manifold vacuum then AC issues.
I do this to make my job MUCH easier: (simplified)
1. remove the right front passenger seat. It makes the rest a piece of cake. 18 mm deep well. Remove the carpet center cover in front of the console.
2. Remove the two 13mm nuts holding the center console.
3. Remove the two other screws on the sides of the console. Remove the center air vent to the rear area,
4. Use a 13 mm socket and remove the two bolts in the front of the engine cover.
5. Use a 15 mm socket with a long extension and remove the top two bolts holding the engine cover.
6. Unhook the ground wire on the driver side.
7. You can now very easy remove the engine cover.
8. On the driver side, the PVC valve sits in a plastic socket. Check both the socket and the top fitting for splits, For $6 replace the PVC valve.
The top of the PVC valve has a vacuum fitting that goes across the engine to the passenger side one way air valve. Go buy high temp hoses and tiny screw down fittings.
9. route the hose behind the air intake over to the passenger side with tie wraps.
10. Replace the tubing the air bottle and water control valve. You can reach both through the right front wheel splash cover.
DO NOT PINCH pennies ain't worth it. Replace all 3. I rarely see the air bottle and water valve fail again as they are not so subject to engine heat.
11. Last one took me 43 minutes.
 
#199 ·
I just read all 10 pages of this thread and now I'm confused.
It seems that for a lot of folk the loss of vacuum means that the controls get stuck on defrost.

On my 94 Astro van however, I used to have great defrost but now it barely works anymore.

I've checked all the vacuum hoses and fixed a few leaks.
The vacuum operated vent flap which switches the airflow from vents to heater outlets works great.
But I get hardly any air blowing up at the windshield on the defrost setting.

Is there another vacuum operated flap just for the defrost setting?
Does anyone know what I may be missing here?
 
#200 ·
The nub that the actuator connects to on the blend door may have broken off... That's what happened to my van. It's in the middle of the dash and you can see it if you pull the console off and peer into that area with a flashlight.
 
#201 ·
Is the fan running? are you getting air movement somewhere?
While you might hear the fan motor running the impeller may have deserted the ship. I had one break off the motor shaft and as soon as all the excess plastic ground away the motor ran great, never sounded so smooth and quiet.
Just wasn't blowing any air....
 
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