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AC blows out the defrost instead of face vents


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Its not bad, drop the kick panel and it will be up to the far right, facing the driver.  Remove the vacuum hose block, clean everything with alcohol or windex and swabs, assemble it while still damp and push to seat all the hoses really good.  Not sure if this is your problem but since I have seen leaks there creating problems, its something to check off the list of potential causes.  

I can not remember if removing the glove compartment helps.

My air delivery would stop on hard acceleration or uphill grades.  Cleaning and reseating that block cleared that up.

Put seat back and tilt the front edge down to give better room.  Its kind of a back breaking position as I get older :D

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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I'll bet it has the same if not close system to the buicks and oldsmobiles. I had pictures and a writeup on another forum on how to repair them but it has been awhile. I would have to try to find it.

GM FAN FOREVER

Nice, clean, luxury= fine automobile

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Your vacuum seems low, I would expect more around 17, and there should be a check valve to prevent loss of vacuum at WOT. Check vacuum directly at the T-body, if it is 15 clean the T-body passages and T-plate.

I would pull the hush panel down on the drivers side and hook a vacuum line from the M-vac to the actuator and cycle it through a couple of times and see how it reacts. You can do it with the vehicle running but plug the line from the programmer and reconnect the P-brake release first. 

As BBF stated the connector/vacuum manifolds sometimes need cleaning and reseating. I have had to "shave" a little off the older style ones because they would actually warp.

THERE IS ALWAYS ENOUGH TIME TO DO THE JOB RIGHT - THERE IS NEVER ENOUGH TIME TO DO THE JOB AGAIN !!!

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I found this old thread on my parking brake and ACM, I tested vacuum and got  20 psi, which seems to confirm OCTs feeling about the vacuum.  

My name back then was Scotty

Brmurph note that you popped in to this thread back then

 

 

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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OK guess Its time to rip into it a little more and see if I can do some more testing.  I have had the hush panels off before and don't remember seeing any vacuum lines (except for the emergency brake), I'll take a closer look,  If all I have to do is drop those panels to test that would be nice.    

BBF nice find on that old post and I certainly remember when you were going by Scotty but I had forgotten about that thread.    I know I have been fighting this problem for a while and when I first opened that old post I thought I had been fighting it for over 10 years (you know how time flys), glad to find that is not the case as back then it was the dealers problem and per the post they got it fixed.. 

Thanks again.  

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We all have been together a long time, its like family!

You will get this done, let us know if we can help

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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  • 3 weeks later...

 I can connect my Mityvac directly to the front dash actuator (I believe #8 on the diagram) and it does leak a little but takes a good 20-30 seconds to leak down so I don't believe this is causing the issue.  That being said it should be replaced and I will eventually do that if it is accessible, as for troubleshooting the search continues.   I then hooked my vacuum gauge in series with the vacuum line that goes to the same actuator and drove around to test/troubleshoot.   When the problem  occurs (AC going to defrost) the vacuum at the actuator quickly goes to 0 and stays there for about 2-3 minutes (meanwhile vacuum at the firewall is still in the 15-20 range) then it comes back to 15-20 and works just fine  until the next time it happens.  I don't think this would be a leak in the line or connection as I think that would be more consistent.  This leaves the controller or vacuum harness actuary valve (leaning to this) which is the valve that all the interior vacuum lines connect to and get distributed.  Anyone have any input on replacing these?  Can't tell if I need to remove the glove box or not, if not it doesn't look fun to replace either of these.

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Very good diagnosis work, very telling.  I think removing the vacuum tubing block from the actuator and cleaning, inspecting and resetting the block first may help, it helped the problem I was having on my 96.  I just cleaned mine, I dont recall if it was possible to redress the ends of the vacuum hoses, I didn't, but it may be clear to you when you get the block off.

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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  • 2 weeks later...

OK I am calling this problem fixed (been a week with no issues).   It was the Vacuum controller (also called vacuum control valve/manifold) mentioned in an earlier post by I believe rockfangd and also BBF (Thanks for that).   My vacuum has gone from a very erratic 10-20hg to a steady 23 hg.  Its interesting at startup and idle it is only about 13-15 hg other then that it is a pretty solid 22-23 hg (at stop lights and what not).  This tells me the vacuum canister must be doing its job.  

Here is a link to rockauto of the part I replaced http://www.rockauto.com/en/parts/acd...rol+valve,7036 . Once you do your basic troubleshooting to verify Vacuum lines are OK and if you are still having a problem I would strongly suggest replacing this valve as it seems to be somewhat common problem, doesn't cost too much and is very easy to replace. To replace it all you have to do is take the passenger hush panel down, reach up and unlatch the valve, remove the vacuum line assembly (unplug it), reverse for the install (had no idea it was so simple until I did it as it sounded like a horrible job to replace :-). I did remove the glove box (also easy) and would probably suggest you do that just so you can see better, I also borrowed the wife's hand mirror (with a base and swivel) so I didn't have to stand on my head to see under the dash. The hardest part was getting the little spring clips off that holds the vacuum block on to the valve (still no big deal). 

If you do have this problem and you want to troubleshoot I would strongly suggest you get a mighty vac, they run under 50 bucks and it can double as a vacuum gauge. I put my mighty vac in line with the vacuum actuator that controls the flow between the face vents and defroster (also easy to do, the line is under the driver side hush panel) and ran it that way for a few weeks, every time I had the problem the vacuum would drop to 0, then after a few minutes it would bounce back until the next time it failed. If you decide to use a mighty vac this way be sure it is not in direct sun as I laid mine on the dash (in July heat in Austin TX) and I think it blew a gasket as it kind of jammed up, I did get it warranted though. 

I can't believe I have been living with this problem so long with such an easy fix.   Anyone else like me and rely way too much on these forums for answers :-) .   Before the net I use to just go after problems until they were fixed, now it seems I have to find the problem on the net first and get answers before I tackle them.  I guess I figure if I can't find the answer in the forums it must more work then I want to complete.  LOL       The interesting thing is I found a lot of post with this problem but very few that provided definite answers and hardly any that pointed to this vacuum valve.  Hope this helps others.     

Thanks again!

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:yupi3ti:

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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