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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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#2 ·
Great post kellowatt , I just did this one the other day myself. Mine was not the tubing to the PCV but there is a vacuum canister under the fan /heater core box. This is where mine was faulty the tubing was restricted from this point. It is a strech to reach this connection I replaced it with 1/4 poly tubing.
 
#4 ·
very well thought out post, though by reviewing the vacuum ball at the base of the vehicle, thats where its actually confusing me, It appears to only have 1 tube going from it, where does the small black vacuum hose run to?

I posted pictures of the tubes, as I may not have it hooked up correctly. The pictures only show one splitter, I have the black splitter, but dont know where it goes, maybe now somebody can help me reconnect this, as the vacuum hoses are brand new from autozone.
 
#11 ·
I don't know if it will work for a 94. The principles are the same, it can't hurt to try.

It's REALLY ironic- I was going to search for this thread tonight. My '06 Express van started doing the same thing this afternoon. I suppose I could tell the fleet manager I'm putting it in the shop, but I'd rather not have the down time.
 
#12 ·
hey olalof,

i have a 1994 and am dealing with the same issues right now also. so far I have replace all the rubber hoses in the vaccum system. I have found that there is a crack in one of the control pieces behind the heater control...i'll have to get a new heater control. You should be able to start tracing these lines from the big black ball that is located under the coolant and windshield washer resevoir. I went from there and started replacing all the lines. I did have the dog house off when I did this...it would be impossible to do without doing it. all tubing and little fitting cost me about $24 at the local napa auto parts.

I should be getting the replacement control unit this coming week and i'll let you know if it fixes the problem. Let me know if you need any other help.

jamie
 
#13 ·
Just did this replacement last night. The part (as you say, #12 in the diagram) was about $10 including tax from local Chevy dealer. For my 2001 Astro, I removed the doghouse and it was pretty easy to feed the hose back from the front to where it connects on the driver side mid-top engine. Also replaced the PCV since it was within a few inches of the vacuum connection. Since the hose had disintegrated within about 1 inch of the fitting in the back, I would never have been able to find where to attach the new hose by looking in from the front of the engine, (nor would two beers have allowed my fat arms to ever fit into that spot from the front) but it was easy to find and access after pulling the doghouse.
 
#14 ·
well i just got in the house after doing all the repair work to the vacuum lines in the engine compartment (last week I replaced all the lines on the driver/passenger side of the firewall).....i now have control over where the air blows out!!!

it was the vacuum lines that go through the fire wall near where the steering column comes through the firewall.

***dead images removed***

It was the two black hoses that are coming out of the firewall that were bad...not just cracked, but looked like battery acid was poured on them. So I cut them about two inches away from the firewall and replaced them about ten inches back into the wire cover goocher.

I also replaced the heater control unit in the dash of the van. The existing control unit had one of the vacuum line connectors broken off and just stuck in the vacuum line doing nothing.

I got it all put back together...a/c was working and the air could blow out and warm my feet or defrost my windshield when the following happenned.

***dead images removed***-new vs. old
***dead images removed***-view from inside

The pieces actually cut a hole in the side of the little area where the blower is spinning (not sure what it's called?). I stuck my camera phone inside it and snapped a picture.

the fan blades that attach to the heater blower motor just exploded....it was loud as hell! i wasn't sure what happenned when it came apart, but it was minutes after I had the doghouse and lines all put back together.

***dead images removed***

this is what the exploded tumbler looked like...imagine the noise that thing was making with all those parts floating around in there.

now i have the new motor/fan assembly installed and it's working great! I can't wait to start it in the morning and have hot air blow on my feet! I hope this helps you olalof, if you have questions, I would be more than happy to help any way I can!
 
#23 ·
Thanks for the writeup. I have a 1996 Astro and have been dealing with heating issues for a while.
I had 2 issues. No vent airflow and fan speed control issues.
I replaced the blower resistor switch last night and resolved that issue, but still had no airflow. I took a chance and searched the forums and found your writeup. I did have a cracked vacuum line. After repairing it, I have air through the vents for the first time since I've owned the van!
Good thing I did it last night as I had a 2.5 hour commute this morning in the first snowfall of the year!
Thanks again!
Ben
 
#25 ·
Something I noticed when I bypasses my heater control valve....My air to defrost only under low engine vacuum went away, I tested the control valve and the diaphragm was the source of the vacuum leak. Just something else for those with this problem to look at. :mrgreen:
 
#26 ·
kellowatt,
Thanks a ton! I just purchased an 04 and it was blowing only out the defrost. I found your post and then went out tonight and found the problem. Line #12 wasn't even connected to the engine and is so brittle it snaps easier then spaghetti! MOst of the other lines are dry rotted so bad thet just crumble.... It'll be a while before I can get in there to replace the lines but at least now I know what the problem is.
Thank You!
Mark
 
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