Author Topic: Center Vent / ACCII Vacuum Issues  (Read 1710 times)

SuitGuy

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Center Vent / ACCII Vacuum Issues
« on: 05 July 2021, 04:01 PM »
So I may not be the most informed on the mystical wonders of ACCII, but I almost bet that my center vents should function! I'm able to get a thin screwdriver and gently pry up the main port and get ventilation to the center vents, but the vent will gently return to closed in a few seconds. I noticed that no blending occurs whenever I switch from DEF to Bi-level or any other option except maybe OFF (I.E, I never have center vents, always have defrosters and side vents). I'm not sure if this is normal, but I would really love some center vents. Anybody know if this is a control panel issue, or possibly a mismatched vacuum setup on my control panel?
Beige 1980 300SD

UTn_boy

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Re: Center Vent / ACCII Vacuum Issues
« Reply #1 on: 06 July 2021, 10:49 AM »
Likely neither.  You probably have a bad/ruptured vacuum actuator that opens the center vent.  In addition, several of the other actuators are probably with ruptured diaphragms on the insides of them. 

The dash and/or the center console will have to be removed to get to most of the actuators.  And no, the aftermarket replacement for the ACCII won't fix the problem, either. 
1966 250se coupe`, black/dark green leather
1970 600 midnight blue/parchment leather
1971 300sel 6.3, papyrus white/dark red leather
1971 280sel Black/black leather
1973 300sel 4.5, silver blue metallic/blue leather
1976 280s astral silver/blue MB Tex

daantjie

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Re: Center Vent / ACCII Vacuum Issues
« Reply #2 on: 06 July 2021, 11:05 AM »
Indeed as Aaron has stated likely you have vacuum leaks all over the show.  Best to invest in a Mityvac or similar style vacuum hand pump and get busy pulling vacuum to at least see where you have leaks.  The large actuator which controls the fresh air flap (blue in colour from memory) is a big culprit for leaks.  You will need to remove the knee roll and panels in the passenger side footwell to get access to it. This is a "fun" game of whack - a - mole unfortunately, no short cuts :-\
Daniel
1977 450 SEL 6.9 - Astralsilber

Engineerd3d

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Re: Center Vent / ACCII Vacuum Issues
« Reply #3 on: 07 July 2021, 01:54 PM »
I bypassed the front actuator door. I simply snuck a copper wire from behind the bled door and wired the center dash opened. Ac works much better this way. I had to remove the vents in the front to help me actuate it opened and wired it open. You can still close the center vent with the knob. Not sure why Mercedes chose to go this complex but this is the deal.

SuitGuy

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Re: Center Vent / ACCII Vacuum Issues
« Reply #4 on: 07 July 2021, 04:47 PM »
Thank you all. Sounds like I'm going to have a fun weekend pulling a vacuum system apart.
Beige 1980 300SD

UTn_boy

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Re: Center Vent / ACCII Vacuum Issues
« Reply #5 on: 08 July 2021, 11:58 AM »
I bypassed the front actuator door. I simply snuck a copper wire from behind the bled door and wired the center dash opened. Ac works much better this way. I had to remove the vents in the front to help me actuate it opened and wired it open. You can still close the center vent with the knob. Not sure why Mercedes chose to go this complex but this is the deal.

Pre 1978 cars with ACC did not have the knob to close the center vents.
1966 250se coupe`, black/dark green leather
1970 600 midnight blue/parchment leather
1971 300sel 6.3, papyrus white/dark red leather
1971 280sel Black/black leather
1973 300sel 4.5, silver blue metallic/blue leather
1976 280s astral silver/blue MB Tex

SuitGuy

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Re: Center Vent / ACCII Vacuum Issues
« Reply #6 on: 12 November 2021, 02:29 PM »
Hello All! I figured I would update everyone on the mysterious nature of 40 yr/old rubber and vacuum systems. I am driving down the road with the fan on BI-LEVEL and my center vent opened randomly and has mostly worked since. I had replaced my blower motor shortly before, so mayhaps some internal pressure from a working blower motor was all that was needed. Thank you all to who have replied, you have been a great help!
Godspeed,
SuitGuy
Beige 1980 300SD

daantjie

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Re: Center Vent / ACCII Vacuum Issues
« Reply #7 on: 12 November 2021, 04:20 PM »
I guess the ACC Voodoo gods are on your side ;D  Did you ever do any vacuum tests?  This is usually the main culprit for the system acting up, if you have any vacuum leaks along the tons of vacuum lines the system will never be 100% right.  As I mentioned the big vacuum pod below the blower motor housing needs a good check over.  If you cannot pull and hold a strong vacuum into this pod then it's toast and needs to be replaced.  I ordered one from Benz not too long ago and they were still available, likely as it is shared with other models using the ACC system like the 123 and 107 models.  Benz has 0% love for the 116 so if you have dedicated parts usually that means you are up the creek :o
Daniel
1977 450 SEL 6.9 - Astralsilber

SuitGuy

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Re: Center Vent / ACCII Vacuum Issues
« Reply #8 on: 12 November 2021, 09:03 PM »
Alas, I have no vacuum tester, but changing that pod can only help, right? Do you happen to have a parts number on that pod? Or is it the standard blue/black check valve?
Beige 1980 300SD

daantjie

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Re: Center Vent / ACCII Vacuum Issues
« Reply #9 on: 12 November 2021, 11:41 PM »
000 800 07 75
Daniel
1977 450 SEL 6.9 - Astralsilber