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1999 Deville
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26 Posts
Discussion Starter #1
Hello I own a 1999 Cadillac Deville and I’m wondering why I only get air through the defroster and not the actual vents. A while back I had air flow blowing through the vents but it stopped. I switched one blend door actuator on the passenger side under the dash but didn’t seem to fix it. Please help I don’t know if there’s another one I need to switch
 

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Registered
2002 Deville and 2009 DTS
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529 Posts
I am not sure about the 1999, but I think there are 3 blend doors.
1 on the passenger side and 2 on the driver side.
 

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Super Moderator
White Diamond '03 DHS (with DTS floor shift)
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87,190 Posts
The pre-2000 Deville's get air from the dash vent ONLY when in the A/C mode.
Heat comes from the floor vents or windshield vents.
Check your owners manual.
 

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1999 Deville
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26 Posts
Discussion Starter #5
The pre-2000 Deville's get air from the dash vent ONLY when in the A/C mode.
Heat comes from the floor vents or windshield vents.
Check your owners manual.
I don’t have the owners manual but I haven’t found anything that it only blows from the defroster or floor vents.
So what your saying is that it’s normal for it to come out from only those or should I look into the second actuator
 

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Registered
2002 Deville and 2009 DTS
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529 Posts
There is at 2nd actuator... look at the pictures I attached previously.
Look at the parts in red circles...# 5 and #25
 

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Master of the Dark Art of Diagnostics
2003 DHS - two-2002 DHS, 2003 SLS, 1995 Sedan DeVille, 1989 Coupe DeVille
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19,857 Posts
your 1999 Deville still has the hybrid system -
electric actuators control the TEMPERATURE -
vacuum motors control MODE - WHERE the air blows from -

also - this is a fully automatic climate control system - except DEFROST -
meaning it was designed for you to simply set the desired cabin temperature
and the system would control the airflow to maintain that set temp -

depending on AMBIENT temperature -
HEAT is discharged from the floor vents -
AMBIENT and COOLED air is discharged through the center vents -

HOWEVER - if there is a vacuum leak -
the MODE will DEFAULT to the DEFROSTER position -

SO - if you select a higher than ambient temperature -
BUT you only get heat from the defroster -
either you have a vacuum leak - OR the vacuum motor controlling MODE is defective -
 

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1999 Deville
Joined
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26 Posts
Discussion Starter #9
your 1999 Deville still has the hybrid system -
electric actuators control the TEMPERATURE -
vacuum motors control MODE - WHERE the air blows from -

also - this is a fully automatic climate control system - except DEFROST -
meaning it was designed for you to simply set the desired cabin temperature
and the system would control the airflow to maintain that set temp -

depending on AMBIENT temperature -
HEAT is discharged from the floor vents -
AMBIENT and COOLED air is discharged through the center vents -

HOWEVER - if there is a vacuum leak -
the MODE will DEFAULT to the DEFROSTER position -

SO - if you select a higher than ambient temperature -
BUT you only get heat from the defroster -
either you have a vacuum leak - OR the vacuum motor controlling MODE is defective -
soo I have replaced a vacuum line above the passenger strut but I still only get AC from my defroster and floor vents.
what’s the vacuum motor that controls the mode? Where is it and would it throw a code? I have none.
 

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Master of the Dark Art of Diagnostics
2003 DHS - two-2002 DHS, 2003 SLS, 1995 Sedan DeVille, 1989 Coupe DeVille
Joined
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19,857 Posts
soo I have replaced a vacuum line above the passenger strut but I still only get AC from my defroster and floor vents.
what’s the vacuum motor that controls the mode? Where is it and would it throw a code? I have none.
=========================
the vacuum motors are NOT monitored - and will NOT set a code if they fail -

there are actually TWO vacuum motors that control the MODE -
GM 1996773 - UPPER -
GM 1996774 - LOWER -
they are located on the "stack" with all the other climate control components -

BUT FIRST - make sure the programmer is getting FULL vacuum -

one very common problem is that the automatic parking brake release diaphragm leaks -
it shares the same vacuum circuit as the climate control system -
 

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1999 Deville
Joined
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26 Posts
Discussion Starter #12
=========================
the vacuum motors are NOT monitored - and will NOT set a code if they fail -

there are actually TWO vacuum motors that control the MODE -
GM 1996773 - UPPER -
GM 1996774 - LOWER -
they are located on the "stack" with all the other climate control components -

BUT FIRST - make sure the programmer is getting FULL vacuum -

one very common problem is that the automatic parking brake release diaphragm leaks -
it shares the same vacuum circuit as the climate control system -
Ohh wow okay so I think I have a problem with the parking break, I manually release it. Is there a common leaking point? Thank you so much btw
 

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Master of the Dark Art of Diagnostics
2003 DHS - two-2002 DHS, 2003 SLS, 1995 Sedan DeVille, 1989 Coupe DeVille
Joined
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19,857 Posts
Ohh wow okay so I think I have a problem with the parking break, I manually release it. Is there a common leaking point? Thank you so much btw
========================
YES - as I stated - the climate control and parking brake release share the same vacuum circuit -
the must common vacuum leak source is parking brake release diaphragm -

one quick and easy test is to remove the vacuum line at the brake release -
plug the hose -
then try the climate control -
 

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1999 Deville
Joined
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26 Posts
Discussion Starter #14
========================
YES - as I stated - the climate control and parking brake release share the same vacuum circuit -
the must common vacuum leak source is parking brake release diaphragm -

one quick and easy test is to remove the vacuum line at the brake release -
plug the hose -
then try the climate control -
Thanks! I’ll try that tomorrow morning
 

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1999 Deville
Joined
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26 Posts
Discussion Starter #15
=========================
the vacuum motors are NOT monitored - and will NOT set a code if they fail -

there are actually TWO vacuum motors that control the MODE -
GM 1996773 - UPPER -
GM 1996774 - LOWER -
they are located on the "stack" with all the other climate control components -

BUT FIRST - make sure the programmer is getting FULL vacuum -

one very common problem is that the automatic parking brake release diaphragm leaks -
it shares the same vacuum circuit as the climate control system -
Hello sorry I’ve been really busy, I have replaced the brake release diaphragm and still nothing. How can I check if the programmer is getting full vacuum? And if I were to pull of a line that leads to any actuator and plug with my finger will I feel it suck my skin in? Need to figure it out soon texas heat is killing me in these black leather seats
 

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Super Moderator
White Diamond '03 DHS (with DTS floor shift)
Joined
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87,190 Posts
How can I check if the programmer is getting full vacuum?
Pull the vacuum line where it enters the firewall on the passengers side and check for vacuum there. That is the supply line. If no vacuum there, follow the line back to the vacuum reservoir and check for leaks in the line or at the reservoir.
 

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1999 Deville
Joined
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26 Posts
Discussion Starter #18
I had this problem for years until I figured out it was the Vacuum controller. Mine is the Concours but I think the base Deville is the same. I did a wright up on this at 99 Deville annoying vacuum problem Post number 20.

Good luck.
Okay so I’ve checked all the vacuum lines under the hood. Confirmed the reservoir has vacuum. The lines up front have vacuum. Also found a shitty electrical tape fix on a solenoid line, worked I guess no engine lights. In the picture with all the colored vacuum lines, is that the vacuum controller? If so i can hear the hiss of air leaking under there. What is it called and can you post a link for me to buy the replacement part. Thanks to everyone that replied.
583381
583380
 

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Registered
98 Concours, 2004 Deville DTS
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193 Posts

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1999 Deville
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26 Posts
Discussion Starter #20
Yes that is it, vacuum control valve/vacuum controller. I know it looks like a mess but I just remember it being easy to replace (all vacuum lines come off together as I recall). I believe this is the part you need https://www.oreillyauto.com/detail/b/acdelco-2729/air-conditioning-16770/climate-control-vacuum-valve-14904/59448b259d5e/acdelco-hvac-control-vacuum-control-valve/1572182/5745386/1999/cadillac/deville
(ac delco 1572182 ).
Thank you ma guy! I’ll order it soon when the pockets get a little heavier
 
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