auto to manual climate control 1984 W126
 

I have not been able to find anything on converting an automatic climate control to a manual system. My 1984 300SD is starting to do funny things that probably necessitate at least a resolder, but I would rather operate the climate control manually.

How many parts make up the automatic system? Or is it just the control that is behind the center console and I can just find a manual CCU from a salvage yard and swap it out? Or are there other considerations?

Thanks ahead of time. :)
Jeff

You haven't found it because it would be an MF'er of a job!! I think somebody is currently doing a conversion, but you have to have another complete manual system, and that is just the starting point.
Fix yours, and have a nice day.......:)

We can only do this in our dreams. As far as I know we are stuck with this.... system.

You could do this only if you get hold of an euro donor car and get the all the wiring and vacuum diagrams to see where everything goes.

Forum member Bruce Kennedy did this successfully using the manual HVAC parts from an '80 240D. You might try searching the DD for posts by him.

Thanks!
 

Thanks all for the quick responses. Yeah, I'll probably just go down the fix-it road for now.

:cool:

It really is a nice operating system and on the 126 it is a little easier to access most of the pods.

What kind of "funny" things is it doing.

(BTW, manual conversion would be a much bigger nightmare!)

funny CCU issues
 

Sam: Thanks!

I just purchased this 24 yr old beauty, so please understand my ignorance.

First, this is all with the 'Auto' feature on, so neither of the fan buttons are engaged. I have pressed the 'auto' button on the far right in order to disengage the manual fan settings.

I am primarily discussing what happens with the 2 buttons that are #3 and #4 from the left. After reading the user manual, it is my understanding that #4 is the 'Economy' mode where the A/C compressor is NOT engaged and you effectively get fresh air from outside that you can heat by turning up the temperature dial. And I believe this air is supposed to be blown in through the dash vents, not the defrost or feet level vents. Then #3 is the A/C button that is supposed to engage the A/C compressor when the temperature dial is set below the cabin temperature. And again, the air should be blown in through the dash vents.

The 'funny' thing that is happening is that the air will usually start out blowing through the dash vents, but then after a few minutes the vent doors will change and blow up through the defrost vents. Then after another few minutes, the vent doors will change and blow through the dash vents. This cycling between the dash and defrost vents will continue when all I want is for cold air to blow out of the dash vents.

Or is this normal operation? :confused:

Sounds like a solder joint issue in the pushbutton controller. This is not as severe or complicated as it may seem at first. If you do a search for "pushbutton controller", "resolering pics" you can probably get some photos of what I'm talking about. Once you open the controller, you will see that the circuit boards are arranged in an "H" pattern. Over time and flexing causes the solder joints to crack where the circuit boards meet. Clean and resolder the joints and it should work like a champ. If you don't feel handy with a soldering iron, find a friend who is and bribe him. It shouldn't take more than about 20 minutes to resolder as there are just a few connections.

Oracle is right. I did the same conversion, but on a W123 a few years ago. When you remove your CC, the wiring harness will come out with the unit, so you probably won't need a schematic. All the vacuum hoses connect to one major line, so just remove all the CC lines. The doner manual unit will be straight forward; no vacuum schematic needed here either. You may have to replace your heater box; I did with mine. This is a bit of a chore, but it's well worth it.

x2

I resoldered the ACC circuit board in Coda and my AC while not COLD is 59F at 45mph. I need to fix the Aux Fan circuit in my AC loop.

another common problem with these systems is the water valve, known as the Mono Valve. It's located inbetween the sub and fire walls near the psgr side. You can get the rebuild kit for about 25.00. Also, there is another two modules in the system. One says something to the effect of temperatureregulator, and is silver... the second which is a relay box is black. I've had the relays go bad and have intermittant operation of parts of the system, soo you may need to clean the contacts. The control box is easy enough to take apart and solder the connections. When you are in the control boxes, if the solder joints are not bright silver, ,and look green or tanish.. get yourself some xylene or acetone and remove the protective covering over the solder joints. You will see the connections have "ring" cracks if they are bad.

Thank you all
 

I am so grateful that you are so very helpful.

Thank you so very much.
Jeff
:D

going to the next step with the climate control
 

Well, I resoldered the CCU (there were some cracked solder joints), but the actuator seems to be stuck on defrost.

I would like to check the relay box. Can you tell me where this is located?

And the silver regulator, what should I look for with it?

Thanks again.

There isn't a relay box on your system. Your system consists of a Pushbutton Controller, Temperature Controller, Blower Speed Control & a set of Switchover Valves. The Pushbutton Controller is the "master" of the system and controls the set of Switchover Valves(vacuum) to direct the air.

Double check F10 & F11 as they provide power for all of this. The switchover valves are electrically controlled by the Pushbutton Controller and use vacuum to drive the pods which are connected to the actuator flaps. Besides the solder joints in the Controller, the next troublesome area is vacuum leaks in the pods, caused by ruptured diapragms. You can access a test point for each of these pods at the switchover valves, located on the passenger side of the console. (Place the passenger seat to the rear, remove the knee panels and carpet, and the screw holding the console side-panel is toward the front. Then the side-panel will slide forward and can be removed.)

When you look at the switchover valves, you will see vacuum lines set up in a "manifold" coming in and then lines which go to each of the actuator pods. Each of the lines going to the pods should hold vacuum. Once you find which ones have failed, you can then determine which pods will need repair/replacement.

On the W126, the dash doesn't need removal but the center pod is the roughest one to access and repair. The others can mostly be accessed behind the glove box and the center console. If you want to go the quickest route and your budget provides room, then pod replacement is the route to go. (Fastlane-search for "vacuum elements") However, several of the pods can be repaired by replacement rubber diaphragms.