Rerouting vacuum lines to have recirculated a/c at all times? - PeachParts Mercedes-Benz Forum

H-townbenzoboy · #1 03-06-2006, 01:36 AM

There was a site that covered this procedure, but it's no longer up. The procedure involved removing the ACC pushbutton panel and getting access to the 5 electric switchover valves that control the center nozzle flap, legroom flap, defroster nozzle flap, main air flap, and fresh air recirculating flap. There was some disabling of valves I think, but definately rerouting and replumbing of these lines to allow recirculated a/c at all times, which cools the car better in Texas summers. Anyone know how to do this?

Thanks

-Joe

my123ca · #2 03-06-2006, 07:18 PM

I think this is what you're looking for:

RE: '83 300D turbo AC issues
James Yuhn (jcyuhn@nortelnetworks.com)
Thu, 15 Apr 1999 09:08:31 -0500

least from this one
OK, fair enough. But first, a disclaimer. This information applies to123 chassis cars with the type III climate control. That'sthe one with five horizontal buttons, fan buttons on the right, and temperaturee dial on the left. This same system appears to have been used on other Chassis (126, 124, 201), but I'm not certain those systems are identical. The MB heating/AC manual I used to devise this change applies only to the 123 chassis.

According to my service manual, in recirculate mode, the system uses 80% recirculated air and 20% fresh air. Now this may be fine in Northern Europe, but here in Texas, it just doesn't cut it. So I set off to improve what I could. Credit must be given to previous list members who first identified the 100% recirc option.

Now, a little background. There are two doors of interest in the HVAC system, the main air door and the fresh/recirc door. These doors are opened and closed to permit or block airflow through specific parts of the HVAC system.

The main air door is located directly behind the glovebox, on the left hand side. It's function is to open or close air flow from the cowl air intakes at the base of the windshield. As released by MB, the main air door is open whenever the HVAC system is on - that is, the engine is running and the HVAC system is in any mode other than off.

The main air door is closed via spring action. Applying vacuum to its vacuum motor causes the door to open, admitting outside air.

The fresh/recirc door is also located behind the glovebox, but on the right hand side. When closed, it prevents air from being drawn into the HVAC system from the cabin of the car. When open, air is drawn from the passenger footwell.

The fresh/recirc door is opened via spring action. Applying vacuum to its vacuum motor closes the door, resulting in fresh air only operation.

If you scan the list archives, you'll find that some posters have disconnected the main air door for the summer and/or cut a small hole in the back of the glovebox to permit manual manipulation of the main air door. I was looking for a somewhat more elegant, automatic, and less invasive solution.

Here's how to re-engineer the system. Supplies you'll need are a few inches of vacuum tubing and a matching vacuum tee - available at your local auto parts emporium for the grand sum of about a dollar.

Remove the wood trim panel which covers the climate control pushbutton unit - it just pops out. Remove the climate control panel via the two phillips head screws in the upper left and right corners. Pull the climate unit out. It's still connected via two electrical cables. Remove these, and put the unit aside.

Located somewhat above and behind the climate unit are the five vacuum valves which activate the various vacuum motors, which in turn direct air flow in your car. Each valve has a rubber vacuum hose connection and an electrical connection as well.

door, fresh/recirc door, and main air door.

Here's how the change works. The main air door is open only when vacuum is applied. The fresh/recirc door is open only when vacuum is *not* applied - they're opposites. Connecting both to the same vacuum source will cause one or the other - but not both - to be open at any time. The result is either 100% fresh air or 100% recirculated air. The vacuum valve intended for the fresh/recirc operation supplies an appropriate source.

Remove the rubber vacuum hoses for both the main air door and the fresh/recirc door from their respective vacuum valves. Push a short length of your new rubber vacuum hose onto the valve for the fresh/recirc function - second from right. Add the tee fitting to the end of this hose. Plug both the hoses for the main air door and fresh/recirc door into the tee. Then disconnect the electrical connector for the main air door from its vacuum valve, which is no longer used.

Reassembly is, as they say, the reverse of removal.

That's it, you're done. There is one change you may notice after this conversion. The main air door immediately flops open or closed when vacuum is applied or released, respectively. The fresh/recirc door, on the other hand, is heavily damped - it requires a few seconds to move from one extreme to the other. Hence when changing from fresh air to recirculated air, there is a short period of time when essentially no air flow is permitted. During this time, you can hear the blower fan change pitch, with perhaps a bit of a whistle as the recirc door begins to open. Such a change takes place when you switch from EC mode (which is always fresh air) to AC mode. Consider it one method through which to verify your work.

- Jim

Jim Yuhn Nortel Wireless Networks Richardson, Texas 972-684-1122 FAX: 972-684-3034

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H-townbenzoboy · #3 03-06-2006, 08:07 PM

Yes! That's it! Thanks very much.

dannym · #4 03-07-2006, 09:03 AM

I read that before too. The problem is I would not want to disable the EC button from working.

Maybe taking this:

Quote:

Then disconnect the electrical connector for the main air door from its vacuum valve, which is no longer used

.
And adding a toggle switch to activate it manually?

DAnny

jcyuhn · #5 03-07-2006, 09:53 AM

I personally think the Internet is our best opportunity for immortality.

Slight correction to the original poster's understanding. This change does not cause recirculated air all the time. Rather, it causes the climate system to use either 100% fresh air or 100% recirculated air. With this change, in EC mode you will always get fresh air. In a/c mode, you will get either fresh or recirc, depending on the temperatures inside and outside the car.

As MB delivered the 123 from the factory it never used 100% recirculated air during a/c operation - 80/20 I think was the split. In a very hot climate (e.g. Texas) introducing 20% humid, 105F air renders the a/c inadequate. So this is a nice fix if you live somewhere seriously hot.

- JimY

soothappens · #6 05-19-2010, 06:42 PM

Just found this thread. Does the 126 model allow 100% recirculated air or is it the 80 / 20 split same as the 123 ?

I think I'm having door issues sometimes ice cold other times cool. This thread will help with the troubleshooting .

jimandsuzy · #7 05-19-2010, 09:46 PM

126 is 80/20 also.

soothappens · #8 05-20-2010, 12:15 AM

Quote:

Originally Posted by jimandsuzy

126 is 80/20 also.

Thanks !

I pulled the glove box out of the 126 and watched the door. A/C in the off position fresh air door pulled closed. Turn on the ac and the door opens about an inch to outside air. You can adjust the amount it opens but it will not fully close . The door rod pivot is threaded.

I guess it works in Germany but not the best in south Texas.

Will the above fix work on the 126 system ? Unlike the 123 the 126 springs open to fresh air if the Vacuum is removed and is held closed by vacuum. Found this out by pulling the vacuum lines loose.

jubjub · #9 06-08-2011, 09:03 AM

A bump for this thread because i'm having an issue with this mod. After a few minutes of driving, the ACC will turn the recirculate vacuum valve on thereby opening the main air flap. I have a tee on the second from the right valve and disconnected the electronic connection for the last to the right valve.

Anyone know why the Air Conditioner would want to close off the recirculate door after 5 minutes of operation?

compu_85 · #10 06-08-2011, 09:46 AM

So that you get fresh outside air into the cabin to keep the driver alert.

-J

compress ignite · #11 06-09-2011, 12:51 AM

NOTHING keeps a driver Awake Like Cold Air to the Forehead!

sjh · #12 06-09-2011, 01:49 AM

In the 124's the recirc pod is 2-stage.

I think that's true of your car as well.

It's fairly straight-forward to "T" together the vac line to the 80% and the vac line to the 20%.

It's also easy to either tie into a permanent vac source or use a vacuum relay and you can have 100% recirc whenever you'd like.

I did it for a bit but reverted back to the standard operation.

Hit Man X · #13 06-09-2011, 06:52 AM

Well 100% recirculated for too long the atmosphere in the car becomes stale. The split works fine for me with R12.

Been over it before, main problems with the early cars are the condenser size and lack of tint... and of course if you are using some other refrigerant.

jubjub · #14 06-09-2011, 07:34 AM

So then the people that are doing this mod aren't really doing much? I had a vac leak in the T I put in, so I could hear when it tried to switch over. Like I said, it started pulling vac after 5 mins. The rest of the 25 minute drive was pulling vacuum. So the people that did the mod are now pulling 100% outside air instead of 100% recirculated air like they hoped?

I just disconnected the electrical connector for the recirc flap, so now I have true 100% recirc all the time. If it gets stuffy, i'll crack a window.

Something else to note was that I though most people said the 85's have the upgraded parallel flow condenser. Mine still has the old tube and fin design. Has mine been replaced?

Hit Man X · #15 06-09-2011, 08:10 AM

Quote:

Originally Posted by jubjub

So then the people that are doing this mod aren't really doing much? I had a vac leak in the T I put in, so I could hear when it tried to switch over. Like I said, it started pulling vac after 5 mins. The rest of the 25 minute drive was pulling vacuum. So the people that did the mod are now pulling 100% outside air instead of 100% recirculated air like they hoped?

I just disconnected the electrical connector for the recirc flap, so now I have true 100% recirc all the time. If it gets stuffy, i'll crack a window.

Something else to note was that I though most people said the 85's have the upgraded parallel flow condenser. Mine still has the old tube and fin design. Has mine been replaced?

It is not a parallel flow in your '85, just a tube and fin with much more efficiency. The tubes are very small in there compared to the early cars... more surface area to dissipate heat. Just search up some pictures online and you will see what I mean.

I will reiterate, most problems are from wrong refrigerant, inefficient condenser, and lack of tint (my '98 V90's A/C was marginal in the summer due to lack of tint as it was like driving a microwave around). Would I love a Sanden/Seltec conversion for my SD? Hell yes... granted the R4 is not the best compressor around, but it is okay when everything else is correct.

Also MB went to different pulleys around '84/5 that spin the main fan faster (motor runs cooler AND A/C is better due to more air volume) plus the aux fan became much larger too. I think the early SD's had a larger metal fan then MB went back to a plastic fan. Not sure why, maybe the metal could not take the higher speeds of the smaller pulley? I know the metal ones I have seen should pull a lot more air just due to blade size.

I just do not see jacking with your vac system as the proper way to go about better cooling. Seems like a 'Band-Aid' when you need stitches.