Alternate title: Ur doing it wrong

I would have posted this while I was in the process of doing it, but I was a bit unsure that it would all work (especially since I was working without a manual). About half way through I started to feel more confident that this procedure was going to work and so, Ive decided to make a writeup of what I did to get to this point.

Why was I unsure that this was going to work? I did this the hard way.

I had read previous posts from “Bruce Kennedy” that he had done this conversion with success. Climate control to manual conversion in this he states that the easiest way to convert the climate control system is to pull the entire heater/evap box and swap them. This is correct. This is the best/smartest way to do this conversion……..but Im not that smart so I did this the really hard way and collected the individual bits and pieces needed to do the conversion.

Again, I urge anyone attempting to do this conversion to swap the heater/evap box wholesale. Less headaches, quicker, less fabrication, etc, etc. But where is the entertainment value in that?

A very thorough guide to removing the heater/evap box can be found here by dmorrison http://www.peachparts.com/Wikka/W123Evaporator . This should guide you through the major steps for the climate control conversion.

Since I did this the stupid-tastic way, it does occur to me that I can point out the areas of contention with both systems and the way I tackled them. So here we go.



The car in question is a 1978 300CD using the oh-so wonderful ACCII system. I think the words “engineered to fail” sum up this system. Hindsight is always 20/20, but how Chrysler thought that coolant, vacuum and electricity would coexist in a little R2-D2 unit is beyond me. At one point there was a severe short that would drain the battery. The short was traced to the servo...solution? Disconnect the servo. This I didn’t like because now the girlfriend was without heat. I replaced the cracked plastic servo with an aluminum bodied servo and got a working auxiliary water pump. For a while there was heat to be had, but only using the defrost function

And then, inexplicably….it stopped blowing heat. Arrrrrgh!

At this point I decided enough is enough. Id had it with the stupid servo and the nightmarish vacuum setup. Winter is on its way again and, while this is California, heat is very useful. It had to go, it was time to take the plunge with the conversion.

The local junkyard tends to have a healthy selection of W123s. At any one time you can probably find 5-7 cars. Sure enough a W123 brown/brown (sorry I don’t know the specific paint/interior color code nomenclature) 240d automatic with a door plaque that said “sept 1977” was there. It was in great shape actually…not really sure why it was there. The interior was intact and it looked like I was one of the first people to touch it. I pulled everything that I could from it….except the heater/evap box.

Naturally the first thing that would help for the conversion is to get a donor car that’s close to the year/generation of the car that you have. Both the donor and the transplant cars were “1978” cars. I imagine wiring diagrams and the like are much closer in the 1978-1980 cars, same for the 1980-85 cars.



here we have the pieces that you would need (if you were as silly as I was and just got the individual parts).

-Bowden cables(four altogether)
-heater valve and hoses
-A/C switch panel
-heater/fan switch panel (not shown)
-240d fresh air/fan vacuum actuator (not shown)
-heater/fan panel fascia
-manual coolant pipe from the engine block
-center vent slide mechanism
-the zip-loc bag has assorted jam nuts, knobs, clips for the Bowden cables, etc
-240d A/C / fan wiring harness (two pieces, not shown)

PS: be very careful when disconnecting the Bowden cables from the plastic levers. Depending on how the plastic has aged it could be brittle. Its very easy to add too much muscle and snap the levers. Take your time, take it easy. It would be a shame to break one of those levers just because you got impatient.



Heres a picture of something important.. these are a couple levers and brackets that NEED to be removed and transferred. No problem right?…Well, heres the thing. The lever to the left can be popped out somewhat easily with a bit of patience but the other lever to the far right is welded onto the shaft. The brackets are riveted on. I have a mini dremmel that I tend to take with me to the yards, but you can see that this is a big pain.

PS: the main heat/fan switch panel on the 240d is riveted to the heater/evap box instead of screwed/bolted on like the auto control switch panel. Mercedes loves rivets. Perhaps you see why I say that its ultimately better to just swap the whole thing…if you still don’t, Ill show you some more fun things.

continued

Gavin