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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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#254 ·
vcbobw said:
This worked perfectly on my 2000 Astro. Also needed to replace the other vacuum hoses in the engine compartments. Hoses and actuators other side of the firewall in the passenger compartment were all fine.

Thanks for the help!
Awesome, congrats on getting it fixed!

Yep, with the under-hood vacuum lines once you have to replace one, might as well replace them all.
 
#255 ·
vcbobw said:
This worked perfectly on my 2000 Astro. Also needed to replace the other vacuum hoses in the engine compartments. Hoses and actuators other side of the firewall in the passenger compartment were all fine.
That was the case with my 2001 Safari. The hose through the engine compartment had gotten too close to the exhaust manifold and it had dried and cracked. When I replaced it, I re-routed it so it was well away from heat sources.
 
#258 ·
ok ...first like all the others ...great post and thank you...

found the check valve... all 3 tubes coming off of valve were broken and about 2 inches long... found the ball and found the intake location... i am sure i looked at it several times but where EXACTLY is the tube coming thru the firewall located? is it just one tube? i seem to remember reading that there are 2...again i know how dumb i will feel when i actually find it ...please help me to be dumb...thanks...Matt
 
#259 ·
Here is the rubber boot thing you mention with the 2 hoses, it is located top left of the opening to the engine bay. I did not investigate but it looks like the hose and boot may be 1 part molded together, so you might have to replace the whole thing with one from a junkyard.

IMG_20200330_074314397.jpg


IMG_20200330_074342250.jpg


https://sites.google.com/site/astrosafa ... ac-airflow
2nd-3rdgen-vac-diagram.jpg
 
#260 ·
yeah ...I am dumb....thank you so much ... 2 tubes was the key...in my defense the hose needing replacing was broken right at the nub and it looked like just the one tube coming out ....thanks again ....Matt
 
#261 ·
so amazon sent me 2 of the tube that goes from intake to check valve.... anyone wants one and near fort collins co I will have on on the shelf in the shop....Matt

edit ...a valve just arrived also and i have extra vacuum tube ...guess i have a kit now ...
 
#262 ·
I just did this without removing the air cleaner. I had my doghouse off anyways as I wanted to get a look in there and I'm going to do a tuneup.
The end behind the doghouse is connected by some sort of t-tap on the same line that goes into the PCV valve. Pretty easy to find. In my case it was a broken elbow which made it extremely obvious.
Once I found that, I just kinda folded it and pushed as much as I could of it over the top of the air cleaner duct that goes into the throttle body.
I came around the other side and it pulled right out and connected to it's place on the front of the van.
I prefer this routing because it protects the hose, and I just have to remember it's there whenever I remove my air cleaner for whatever reason (Will do it soon to clean throttle body and possibly do an MPFI upgrade with a $100 spider that I found).

I turned on my blowers and woo! I got air. All of the modes seem to be working properly, (you can hear the system get closed once you put it on max AC), so pretty soon I'll see if I can do some kind of pressure test on the HVAC system, and if there are no leaks, or if the leakdown is extremely minimal, i'll recharge it.

2 minute job if you do it like that.
Just thought I'd throw that in there in case anyone removes their air cleaner as a first step.
 
#263 ·
gman said:
I turned on my blowers and woo! I got air. All of the modes seem to be working properly, (you can hear the system get closed once you put it on max AC), so pretty soon I'll see if I can do some kind of pressure test on the HVAC system, and if there are no leaks, or if the leakdown is extremely minimal, i'll recharge it.
If there is any leak you should fix it properly before you charge it.
 
#264 ·
AstroWill said:
gman said:
I turned on my blowers and woo! I got air. All of the modes seem to be working properly, (you can hear the system get closed once you put it on max AC), so pretty soon I'll see if I can do some kind of pressure test on the HVAC system, and if there are no leaks, or if the leakdown is extremely minimal, i'll recharge it.
If there is any leak you should fix it properly before you charge it.
How do you fix leaks without ripping the entire system apart? Replace the lines or use a pipe clamp?
 
#265 ·
Most of the leaks occur at the compressor belly seal, the compressor to pipe seals or the o-rings in the system.

If it's a line there are various ways, but usually the best is to simply replace the line.
 
#266 ·
AstroWill said:
Most of the leaks occur at the compressor belly seal, the compressor to pipe seals or the o-rings in the system.

If it's a line there are various ways, but usually the best is to simply replace the line.
Thanks. The air actually gets pretty cold fairly quick, but it just seems "weakly cold" rather than just a blowing of air, which is what an A/C'less car feels like.
But, ultimately the pressure test will show. I'll check those areas if it shows any leakdown.
If not, i'll recharge and have cold air (though it's a pretty low priority honestly).
 
#267 ·
So I'm seeing the same issue on my 2002 Astro. Rear AC is blowing ice cold but there's no air coming from the front vents. There is air coming out of the front floor vent, the windshield defroster, and the mirror defrosters but it's not cold. What percentage of the time is the vacuum line noted in this thread the cause of this problem?

I didn't pull the air cleaner off yet but when inspecting the line it appears to be attached and I can't see any visible cracks. If it's not this line, what else could be causing this?
 
#268 ·
Check the line from end to end. The elbow could be split or loose, the line anywhere along the length can be cracked.

If it's intact, time to check all the other vacuum lines and check valve that the suspect line attaches to on the passenger side of the engine bay.
 
#269 ·
Leeann_93 said:
Check the line from end to end. The elbow could be split or loose, the line anywhere along the length can be cracked.

If it's intact, time to check all the other vacuum lines and check valve that the suspect line attaches to on the passenger side of the engine bay.
So I did a more thorough inspection of the line, and still didn't see any visible cracks and it appears to be attached on both ends because I can pull on it and it doesn't move. Should I just buy the part and replace it anyway? How small of a crack or hole can cause the issue?

Is there a diagram/video/post that details how to check everything else you mentioned that may be causing the issue?
 
#271 ·
Leeann_93 said:
Look back a page.
Okay thanks, I hadn't quite finished looking through the whole post yet. So I should check vacuum lines first, then the check valve?

Going back to my last question, how small of a hole can cause issues? Should I just replace the line noted in this post anyway if it's the most common cause of this issue?
 
#275 ·
I looked through this post but no one really seemed to address my question. If the line shown in the original post doesn't appear to be cracked after a visual inspection, should it still be replaced since it appears to be one of the most common causes of no AC out of the front vents? What's the order I should follow when trying to diagnose what's causing my problem?

-where are the other lines located and can they be changed following the same procedure?
-do the other lines have specific GM part numbers or can I just use vacuum tubing from the auto store? It seems like some people have done it this way.
 
#276 ·
Gu3nth said:
I looked through this post but no one really seemed to address my question. If the line shown in the original post doesn't appear to be cracked after a visual inspection, should it still be replaced since it appears to be one of the most common causes of no AC out of the front vents? What's the order I should follow when trying to diagnose what's causing my problem?

-where are the other lines located and can they be changed following the same procedure?
-do the other lines have specific GM part numbers or can I just use vacuum tubing from the auto store? It seems like some people have done it this way.
:banghead:
 
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