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AC blows out the defrost instead of face vents


brmurph

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I have a 98 Concours that the cold AC starts blowing out the defrost vents intermittently even though I have it set for the face vents. This has been happening for a few years but now seems to happen multiple times in a short drive. My first thought of course was a vacuum problem but I have some what ruled this out as the problem never seems to happen when I do a WOT when I think vacuum should be at its lowest and I have had it happen during deceleration when vacuum should be at its highest, also the emergency brake release works fine. Keep in mind the Concours has the sporty dash like the 97 and older Sevilles.

Thanks in advance..

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Check the OBD codes. It seems you have an air mix door sticking, or its vacuum line is off. The codes will tell which one.

CTS-V_LateralGs_6-2018_tiny.jpg
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-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data
-- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC
Yes, I was Jims_97_ETC before I changed cars.

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check for strong 16-20" on vacuum in the engine compartment vacuum feed harness. There is one feed vacuum hose for the inside HVAC system and its located on the right side of the car near the rear valve cover. It has a funny connector on it and feeds into the wiring harness inside the car. Just unplug it and check it with your finger for vacuum.

Edited by barczy01
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I have a few history codes, nothing current. IRC1780, B0856, B1983 . I don't think any of these are related but I could be wrong (had trouble finding code definition on some of these codes).

My vacuum gauge is loaned out so I will have to verify that later but I did pull apart the connection you suggest and I can feel a vacuum (not sure if it is enough or not). I also pulled the same connection about 20 seconds after I turned the car off and there was still vacuum (which suggests to me no real big leaks :-).

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enough to stick to your finger? I just had a car with the same issue and it had slight vacuum at that connection, ended up being a partial plug vacuum port at the throttle body.

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enough to stick to your finger? I just had a car with the same issue and it had slight vacuum at that connection, ended up being a partial plug vacuum port at the throttle body.

Yes it did seem to stick to my finger. I'll get my gauge back and report the results. BTW can you elaborate what kind of vehicle you were working on and if it was a Northstar give me a little more details like where the partially plugged port is ? Is it an easy check ?

Edited by brmurph
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B1780 Theft Lock Enabled
B0856 Battery 2 Out of Range
B1983 Device Power Circuit Low

None of these show a stuck air mix door. I was expecting something like

B0130 Air Temperature/Mode Door Actuator Malfunction

You might check and see if these codes are exactly what is reported on the DIC. The first one says that the radio isn't sure it hasn't been put in another car and the other two show a low or bad battery. A low battery or bad battery cable can cause all sorts of bogus codes. So, I would suggest that you clean your battery cables and check your battery and make sure that it is fully charged, clear the codes, and see what comes back.

It may turn out that all you need is to clean the battery cables or charge the battery, or perhaps a new battery.

CTS-V_LateralGs_6-2018_tiny.jpg
-- Click Here for CaddyInfo page on "How To" Read Your OBD Codes
-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data
-- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC
Yes, I was Jims_97_ETC before I changed cars.

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Yeah those are the codes. I could be wrong but since this is a vacuum actuator and not electric I doubt it will set a code. The battery gets replaced every couple of years and the alternator about every 3 :-). Currently I think the electrical system is working OK.

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  • 2 weeks later...

Here are my results from a vacuum check. BTW I added a tee into the system and put the gauge off that so the climate control is included in the test. At idle I would get about 15-18, it seemed to be a little less with the air conditioner on (15 range) but I think still acceptable. I then took a page from the Guru by taping the gauge to the windshield and driving around for a week waiting for the failure. What I found is with the climate control off and cruising down the road the vacuum was a very solid 20 (by solid I mean it did not fluctuate but just an inch or two either way regardless where the throttle was (uphill, downhill, starting, stopping, etc). With the climate control on and AC on the vacuum did fluctuate a bit more from a low of about 10 to a high of about 18 (it seemed to stay around 14 most of the time). Seems that the climate control system maybe leaking vacuum a little but not enough to cause problems (that's my thought anyway)?

Things to note:

1. At one point going up a hill with the AC on the gauge did get down to just 3-4 just for a second or so but the AC never missed a beat (continued blowing out the face vents). .

2. I had failures occur when the vacuum was at its highest and I had absolutely no problems when the vacuum was at its lowest.

3. After shutting off the car it would take about 30 minutes for the vacuum to drop to 0 with the climate control system set to off. With the climate control on it took maybe 15 minutes to go to 0 after I shut the car off.

Thanks in advance.

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They run along the right framerail and dart out to the rf of the car to a vacuum canister. Check the vacuum source at the throttle body where there is a funny snap in connector. There are little needle passages in the throttle body that get clogged with carbon.

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I guess I should have mentioned it but I have kind of ruled out a vacuum problem based on the data I posted above (unless someone sees something in the data that I don;t). My question now is what else could cause the AC to blow out of the defrost temporarily besides vacuum? Any other thoughts?

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I don't think the vacuum should drop to 15" with the A/C on - to me, that indicates a problem - leak in the circuit.

Kevin
'93 Fleetwood Brougham
'05 Deville
'04 Deville
2013 Silverado Z71

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Agreed and I am sure your right but it doesn't seem to be effecting the vents (in my opinion). I am assuming you would disagree and you may be right, I will take a look at those lines soon. The other thing the above data means to me is if there is a leak it is most likely in the climate control area (which I really don't want to go into if I can help it, or at least not until I have more confidence that is where the problem is :-) since it is only when the climate control is on that the vacuum goes a little low.

Thanks.

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  • 3 weeks later...

Has anyone mentioned about the parking brake release diaphram?

I would pop the vacumn line off of that and test the diaphram. It is located right behind the parking brake pedal.

IIRC it is in the same vacumn lines as the HVAC

GM FAN FOREVER

Nice, clean, luxury= fine automobile

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Has anyone mentioned about the parking brake release diaphram?

I would pop the vacumn line off of that and test the diaphram. It is located right behind the parking brake pedal.

IIRC it is in the same vacumn lines as the HVAC

Not in this thread but I have heard about it in the past. The parking brake works fine so I kind of ruled that out. Also the problem occurred when the vacuum was in the normal range so I have kind of ruled vacuum out as a cause. Thanks though!

I would like to mention again that this is a Concours so the climate control is like the older STS and Eldorado's and not like the standard Deville.

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  • 1 year later...

1998 Concours 

Note: has center console so the hvac is like the 1997 and older sevilles  and 2001 older eldorados

Update to this problem but still fighting it :-(.     I have had to fix a few problems over the last couple of years to really get this car road worthy again and except for this problem (which is big since I live in Texas) the car is running well (with help from this board, thanks for that).   I bought a mightyvac which has been extremely useful and has helped me find a few small leaks.  The vacuum (except for maybe in/under the dash) now seems to be leak free and working well.  The problem has improved noticeably  after fixing the leaks but it still exists and is extremely frustrating when it is 100 degrees outside.   

Currently the emergency brake is out of the circuit (and still have the problem),  I have the mighty vac connected to the output to do some testing.  This testing was all done with the mighty vac as I blocked off any engine vacuum.  What I found is it only takes about 3-4 (I guess HG) to get the vents to go from defrost mode (default) to the face vents.  I can create enough vacuum with the mighty vac (hand pumping)  to get the air to blow out of any vent however the face vents was the toughest (it tended to leak out faster then I could pump with the mighty vac) but that was intermittent, at times it leaked very fast (could barely get the gauge to 5 HG and other times it would hold a little vacuum (could get it up over 20).     To me because it is intermittent seems to point to either the controller or the programmer as I feel if it was a leak in a line or diaphragm it would be consistent.  I am leaning to the programmer as my understanding is that is where all the vacuum connections occur.   My concern is I have never read about anyone replacing either of these for this type of problem so I guess I am a little nervous to replace them, anyone know which is easier to replace :-)?    One more thing to note is with the car off and the mighty vac connected to the line going into the firewall there are no leaks.  

Hope this makes some sense.  Any experience with the controller or programmer would be appreciated.  

Thanks.  

Edited by brmurph
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Please feel free to correct me if I am wrong but I remember the buicks had issues with the programmers (the module that the vacuum line goes to)

because the rubber nipples would dry out and close off the ports. I have not run into this with a cadillac but you are on the right track. 

The part with the nipples I am referring to is square and has several colored lines coming out of it. I have corrected the problem by doing away with the plug and splicing the vacuum lines together. 

On another note  have you checked the line at the firewall to see if it is pinched?

On certain temp days a pinched line may work better  or worse. Usually on cooler days it will work better but hotter it will be soft enough to pinch off.

Thanks for updating this. Glad to hear your concours is doing well.

GM FAN FOREVER

Nice, clean, luxury= fine automobile

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I corrected a lot of problems on the old style programmer but the one in your vehicle is different.

I couldn't find a pic from a Deville but the one I found was from an Eldo / Seville. The programmer should be the same basic design and operation though.

What is source vacuum now?

Sounds like an actuator #8 leak or diaphragm / door sticking.

 

2013-01-07_195455_1.png

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

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Thanks guys.  I had the problem again this morning, no air from the face vents for about 3-4 minutes then it came back and worked fine (vacuum was over 15 the whole time).  

Rockfangd I don't believe the line is pinching as I have a vacuum gauge hooked up on the inside of the car and the problem happens when the vacuum is fine (15-20).  The line looks fine by looking at it but good point about temperature and it possibly collapsing in the heat.  I have seen the vacuum drop down to 10 (very rare) and have never had the problem, it only seems to happen when it is over 15.   

Oldcadtech, thanks so much for that pic, it helps a lot.  I have the factory manuals but have not found anything that descriptive.   You might be right about the # 8 actuator, guess being intermittent and only happening when the vacuum is good is making me think something else.    Currently the vacuum is coming from the intake manifold (like it is suppose to be)  but during testing I had my mighty vac connected to the emergency brake vacuum line, I had to put it in gear to get vacuum through it but seems to work well for testing, this is also where my vacuum gauge is connected while driving down the road (easy access to vacuum :-).  

So here are the possibilities as I see it and in the order of most likely.  

1. AC defroster actuator

2. Programmer

3. Controller

4. vacuum control solenoid based on this thread .   http://www.cadillacforums.com/forums/cadillac-seville-cadillac-eldorado-forum/266345-low-vacuum-mode-doors.html

Any suggestions which one of these are the easiest to test or replace?  I don't really want to take the whole dash apart :-(..  

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On my 96, I solved my problems by removing, cleaning and resetting the vacuum connections at the vacuum actuator valve #2 at the programmer #4

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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23 minutes ago, BodybyFisher said:

On my 96, I solved my problems by removing, cleaning and resetting the vacuum connections at the vacuum actuator valve #2 at the programmer #4

BBF thanks.  How hard was it to get to that?  Just pull out the glove box and you have access?

Thanks.

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