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  #1  
Old 06-27-2008, 02:13 AM
JimmyL's Avatar
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W123 difference between Recirculate/Fresh air flap and Main air flap

My reference threads I was looking at are

Main air flap? Why??

and

W123. My experience with replacing all AC vacuum elements without removing the dash.

My '85 wagon will not pull in the main air flap, and it causes the center vents to close after a while. I can push it a little {removed glove box} and as long as I push it left {open} to start out, the vac will pull it over and keep it there and the center vents remain open.
I guess I need to pull it apart and check the diaphram, but I just can't figure out the functions of the two flaps mentioned above.
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Jimmy L.
'05 Acura TL 6MT
2001 ML430 My Spare

Gone:
'95 E300 188K "Batmobile" Texas Unfriendly Black
'85 300TD 235K "The Wagon" Texas Friendly White
'80 240D 154K "China" Scar engine installed
'81 300TD 240K "Smash"
'80 240D 230K "The Squash"
'81 240D 293K"Scar" Rear ended harder than Elton John
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  #2  
Old 06-27-2008, 07:37 AM
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maybe....a clue?

Hey Jimmy.

Maybe my most recent AC center vent & defrost vent issues will give you a clue. About 2 weeks ago, I noticed that when I have AC on......and I just started the car.......and I'm at "low idle"....that the flap\pod that keeps the AC coming out the center vent instead of DEFROST will change to the DEFROST position.

I think it is low vacuum. I don't think I have a vacuum leak in my lock system --- car can stay locked and unlocks after sitting for weeks. However, I think there is sometype of leak in my climate control pod circuit. It may even be in the actual pod. When I replace my dash, I will be giving every vacuum component a double look over.

It will probably take me 30 hours to replace my dash --- AC and radio issues. UGH.
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  #3  
Old 06-27-2008, 10:18 AM
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I have been trying to figure out the exact same thing. Which positions do what?
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My Primary Driver - '85 300CD - 4-speed conversion, 2.47 rear, lowered, euro headlights, rebuilding (not restoring so much)

Wife's - '08 Saab Sportcombi Aero

Riding a '03 Yamaha Warrior
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  #4  
Old 06-27-2008, 11:20 AM
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Jimmy,
IMHO, it could be in the pod, it could be low vacuum, it could be the CCU. In my 83, I think all of my PODs are showing signs of age and I could spend every weekend chasing vacuum leaks. I'm considering some manual overrides:
In another thread, someone advocated disconnecting the center vent pod, tying the flap open with a zip tie, and pluging that vacuum line. That would leave the center vents open all the time and I think I would like that. In normal operation in winter, the center POD is closed and heat only comes out the side vents. I think I would like heat out the center also. The only down side of blocking the center flap open according to Sam Ross is possibly starving the windshield in defrost mode. I can control that on mine as my center outlet nozzles can be closed.

I'm also considering tying my fresh air/recirculate flap in the recirculate mode and pluging that line also. I'm a non smoker and could let in some fresh air as needed with the window. But in Texas summer, recirculate is where the best cooling would occur and that's my priority.
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1983 300D, bought new, 215k+ miles, donated to Purple Hearts veterans charity but I have parts for sale: http://www.peachparts.com/shopforum/mercedes-benz-cars-sale/296386-fs-1-owner-83-mb-300d-turbo-rebuild-parts.html
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  #5  
Old 06-27-2008, 11:34 AM
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Quote:
Originally Posted by Cr from Texas View Post
Jimmy,
IMHO, it could be in the pod, it could be low vacuum, it could be the CCU.
I've put in 2 different CCU's and I know it isn't that. I'm sure it's a vac issue. I had a very high pitched whistle from under the dash prior to this happening. It only whistled at idle and it was extremely loud. That has gone away and this problem has become less erratic and more consistent. I'm sure the whistle was a pin size hole in a diaphragm that has now gotten larger.


Quote:
Originally Posted by Cr from Texas View Post
I'm also considering tying my fresh air/recirculate flap in the recirculate mode and pluging that line also.
So, which direction of the fresh air/recirculate flap is recirculate? The flap all the way to the right closes that opening over the squirrel cage fan, but my pea brain can't tell which is fresh air and which is recirculate.
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Jimmy L.
'05 Acura TL 6MT
2001 ML430 My Spare

Gone:
'95 E300 188K "Batmobile" Texas Unfriendly Black
'85 300TD 235K "The Wagon" Texas Friendly White
'80 240D 154K "China" Scar engine installed
'81 300TD 240K "Smash"
'80 240D 230K "The Squash"
'81 240D 293K"Scar" Rear ended harder than Elton John
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  #6  
Old 06-27-2008, 11:38 AM
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OK, so I am out here messing with the climate control vacuum pods right now in my '85, and saw their opening technique.

Setting Main Air Recirc
Defrost Vac Vac
AC full arrows No Vac No Vac
AC half arrow Vac No Vac (is coldest on my system by 5-7*)
EC Vac Vac

Now, given my car was set up correctly when I bought it, looks like the recirculating valve is normally set to recirculate. Main air seems to be set to not let outside air in.

Just for the record, the main air vac line is hooked up all the way to the right vacuum supply behind the ACC unit. The recirc is hooked up to the second to right. Is this what others have? I figured it would be the other way.

I really don't understand the purpose of the main air valve. Doesn't the recirc valve control if you get outside air in the system?
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My Primary Driver - '85 300CD - 4-speed conversion, 2.47 rear, lowered, euro headlights, rebuilding (not restoring so much)

Wife's - '08 Saab Sportcombi Aero

Riding a '03 Yamaha Warrior

Last edited by lowriderdog37; 06-27-2008 at 11:22 PM.
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  #7  
Old 06-27-2008, 11:55 AM
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I thought the extreme right hand flap was the fesh/recirculate and the default mode (no vacuum) was fresh. I'll send an email to Sam Ross and ask him to join in as he has a air "suitcase" out of the car.
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1983 300D, bought new, 215k+ miles, donated to Purple Hearts veterans charity but I have parts for sale: http://www.peachparts.com/shopforum/showthread.php?t=296386
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  #8  
Old 06-27-2008, 05:27 PM
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I had the same problem when the pod on my main flap had a leak - the center vent wouldn't open.

Since the swithcover valves all have the same vaccuum source, it makes sense. replace the leaky pod, and I bet you'll be fine.
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  #9  
Old 06-27-2008, 05:51 PM
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Quote:
Originally Posted by lowriderdog37 View Post
I really don't understand the purpose of the main air valve. Doesn't the recirc valve control if you get outside air in the system?
You are correct. The fresh/recirc flap controls whether or not fresh air enters the system.

The main flap is open whenever the cc is on ( any of the 4 left buttons ), and closed when it's off. My guess is that it's purpose is to keep the moldy smell of the evaporator core from entering the cabin. When the system is on, the core and cabin have air passing through them, so the smell is dissipated after a few seconds.
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  #10  
Old 06-27-2008, 07:02 PM
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Charles asked me to join this THREAD… !

Quote:
Originally Posted by Cr from Texas View Post
I thought the extreme right hand flap was the fesh/recirculate and the default mode (no vacuum) was fresh. I'll send an email to Sam Ross and ask him to join in as he has a air "suitcase" out of the car.
Quote:
Originally Posted by theo3000 View Post
You are correct. The fresh/recirc flap controls whether or not fresh air enters the system.
The main flap is open whenever the cc is on ( any of the 4 left buttons ), and closed when it's off. My guess is that it's purpose is to keep the moldy smell of the evaporator core from entering the cabin. When the system is on, the core and cabin have air passing through them, so the smell is dissipated after a few seconds.
Yes, you can blame Charles of Texas for what turned out to be a somewhat long-winded POST!

So let me give my $0.02 worth and comment mainly to the above… but first let me tell you a little of the project from which I have gained my knowledge on this subject:

I am in the final stages of a complete SERVO rip-out and AUTO-to-MANUAL conversion of my Son’s 1980 300D’s ACC system. I canNOT tell you how happy I was to rip out that god-awful SERVO and all those vacuum and electrical wires running through the firewall directly under the battery pan where the vacuum line particularly took a beating… and of course I don’t have to tell you the drawbacks in trying to repair and maintain any of the older SERVO-based ACC systems!

Well except for the 5 vacuum “PODs”/elements, he no longer has any automatic ACC components. I started by picking up a 1978 240D model “suitcase” and manual AC/Heater controls. By “suitcase” I am talking about the entire black plastic encasement that fits under the dash/behind the console… and it contains the EVAP and HEATER coils/cores, air dampers/flapper air valves and associated actuator PODs/elements mounted on the exterior [Cost ~$100]! My original main interest in this was to get the manual AC compressor temperature control that cycles the compressor on/off, the blower motor speed control, and the two manual heater controls. When the salvage guy offered the entire package for very little $$, I took it and glad I did… for this allowed me to study the inner workings of the suitcase and for the first time understand how the airflows are controlled by the various dampers.

Hot air from CENTER nozzles – For all practical purposes this is an impossibility for the air flowing out of these nozzles is “scooped” from the airstreams flowing from the EVAP but before it passes through the HEATER core. I have also heard for safety reasons that the German engineers did NOT want the system to be capable ot blowing warm air in the face of the driver. Kind of makes sense!

Now that I have full/separate manual control over all five damper/POD pairs, I did find that IF you position all the controls as follows:
[1] RECIRC damper in the recirculation position [vacuum applied]… this to increase air flow to maximum
[2] DEFROST damper closed [vacuum applied]…
[3] LEGROOM damper closed [vacuum NOT applied]… AND
[4] CENTER nozzles damper open [ vacuum applied ]
I found that the air flow is so great with max Blower speed what happens where the air is normally “scooped” up out of the top of suitcase… well some air still flows through the top of the HEATER core and eddies its way back through the bottom of the core and mixes with the turbulent air heading for these two CENTER nozzles! So at best you can only get “warm” air and only IF you have full manual control as my project allowed me to have. I would not recommend this project for this intended goal alone. My project was embarked upon mainly for: (a) reasons of economy , and (b) simplicity/reliability. I am also replacing the old condenser with a parallel-flow type. I am installing a new compressor and having 4 hoses fabricated that will not leak R134a gas as I’m sure the old hoses did… and this is 2 hose less than the OEM 6 hoses on these systems. Of course I’m replacing the Receiver/Drier, safety switches, and flushing the EVAP. I have even figured out how to somewhat easily clean the exterior of the EVAP coil without having to remove it!

What’s the “ MAIN ” air damper/POD/element for – Here is my explanation. I think this is partially a carryover from the earlier mostly manual systems in Europe where AC was not very common back just a short while before these 70/80(s) models were rolling off the assembly lines. Then as the U.S. market heated up and demand surged, the German engineers got the notion that only an integrated fully automatic AC+HEAT system would exude the “ LUXURY ” they thought appropriate for their name… so they looked around to see how to get something installed ASAP and at first they bought the heart of there god-awful SERVO system from Chrysler ~mid-to-late 1970(s) and I’m sure regretted it within a very short time. I guess their redesign of the automatic ACC systems without the SERVOs began rolling off the lines in 1981!?

Back to the subject… MAIN air dampers. IMHO in the previous MCC manual systems [before AC] this damper was mainly needed to shut off the ice cold FRESH air that would filter into the suitcase and ventilation system during the winter when it was NOT really cold enough for the HEATer… And then later as AC was added, they realized that too much fresh air was not good for cooling in the SUMMER. But one basic design concept was to keep at least 20% FRESH air flowing into passenger compartment [summer and winter]… this to insure the driver was not subjected to too little oxygen… a SAFETY issue. So what we have in the ~1978 to current models is a MAIN FRESH air damper and the RECIRC air damper that both work to minimize cold air infiltration when the MCC or ACC us “OFF” and when the Blower fan is working in any mode there is at least 20% FRESH air being introduced for the [passengers. To the best of my knowledge of this whole range of models/years of these MCC & ACC systems, they work such that you either have 20% FRESH [synonymous with 80% RECIRC] OR 100% FRESH air.

And finally my future 100% RECIRC Mode! – Yes I have also figured out how to make both Manual systems [ MCC ] and automatic [ ACC ] have a full recirculation [ “ Max AC ” ] mode… by modifying the surface of either the “ MAIN ” or “ RECIRC ”damper flapper valve… but my final comments/advice on this will have to wait until I finish this project in a month or so. I think this feature would be of most interest to those of you who have to deal with stiffling humidity along with HOT summers!

I hope this was of interest… and maybe even helps some of you out there !
Sorry but NO, I did NOT study the automatic controls enough to answer questions about those "buttons" and what is suppose to happen when. I concentrated on learing the suitcase and how to give the driver as much manual capability as is " practicable " !
Best regards,

Last edited by Samuel M. Ross; 06-27-2008 at 07:04 PM. Reason: minor edit "tweak" !
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  #11  
Old 06-27-2008, 08:49 PM
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Sam,
Thanks for jumping in. That was the detail I hoped you would add for those of us that want to maximize the seasonal output of the system. Let us know your final conclusions next month.
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1983 300D, bought new, 215k+ miles, donated to Purple Hearts veterans charity but I have parts for sale: http://www.peachparts.com/shopforum/showthread.php?t=296386
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  #12  
Old 06-27-2008, 10:31 PM
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Can't wait for the finished product, but the information has already been very helpful!!!!!
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Jimmy L.
'05 Acura TL 6MT
2001 ML430 My Spare

Gone:
'95 E300 188K "Batmobile" Texas Unfriendly Black
'85 300TD 235K "The Wagon" Texas Friendly White
'80 240D 154K "China" Scar engine installed
'81 300TD 240K "Smash"
'80 240D 230K "The Squash"
'81 240D 293K"Scar" Rear ended harder than Elton John
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  #13  
Old 06-27-2008, 11:36 PM
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Thanks for all that good info!

It looks like my vacuum pods are hooked up wrong. I am going to go out there tomorrow and make a spreadsheet and figure out how to correct them. I just noticed that my pretty little graph from earlier didn't save the spacing...sorry about that.

One more question for you Sam. With the main valve, which setting (vac or no vac) controls weather it's 20% fresh, or 100% fresh? I am guessing vac gives 20% fresh because my system has it (see ugly graph from earlier) and it's colder.
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Wife's - '08 Saab Sportcombi Aero

Riding a '03 Yamaha Warrior
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  #14  
Old 06-28-2008, 08:11 PM
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OK, well I've spent the better half of a day working on my climate control, and I think I've figured it out (at least for my '85 300CD). I went through all the functions of the ACC, along with all of the vacuum elements and how they control each other. I have the spreadsheet made out, I can't really post it here so you could read it, so if you need it, pm me.

I found that the defrost vents are normally open, feet and fronts are normally closed. The recirculation is normally set to recirculate, and the fresh air is normally set to 20% fresh.

In the end, I decided to disconnect the second line to the defrost element (connected to the front vents). Then connected the front vents vacuum line to the foot element.

Like I said before, I don't know if mine was hooked up correctly when I bought it, but I am pretty happy with the setup I have now.
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Wife's - '08 Saab Sportcombi Aero

Riding a '03 Yamaha Warrior
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  #15  
Old 06-29-2008, 12:31 AM
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I'd like to see the spread sheet. PM sent.
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