W123 AUTO TO MANUAL CLIMATE CONTROL SWAP WIRING HELP - PeachParts Mercedes-Benz Forum

84-300dee · #1 03-25-2015, 10:10 PM

Hi All,

I'm in process of converting my 84 300D Type III Auto climate control to a 81 240d Type I (later style with vertical A/C wheel) manual climate control (only ONE vac line in the system

) Thank you for the writeups/advice I've used on here!

I don't like auto climate control and don't use it even though I have it in my newer vehicles. Tried to fix the Monovalve, but no success, heat always on overpowering A/C... Looking to simplify and increase reliability/remove potential leak points at firewall etc.

I took the entire box and associated parts from the donor and cut it from the big wiring harness to the left of the box.

In the various swap threads, it was mentioned that you should take the manual hvac harness, but I found it is not detachable and part of the whole dash harness so I traced the HVAC wires to this big bundle and cut from there.

Can anyone who has successfully done this swap care to share/help with wiring this into later 300d (or do a write up)? The MB hvac service manual online is unreadable/badly scanned.

Thanks so much!

84-300dee · #2 04-05-2015, 11:31 AM

Sorry for the all caps in the subject line, tried to edit but I couldn't change it... Didn't mean to come across as shouting.

After studying both system schematics (my head still hurts!) I have managed to complete the swap. I am no electrician by any means.

As mentioned previously, when attempting this swap, cut the manual hvac box from the main harness to the left of the unit, as well as the smaller harness to the left and behind the floor ducts. Don't remove any wiring from the manual box itself.

There are only about three wires to splice in the cabin. Grab power from the existing blower (redwire) and ground from the "geblasereglar" (blower regulator) located on the passenger side behind the glovebox. You rejoin the bigger and smaller harness wires back together from the manual box (they match in color)

In a previous write up the "geblasereglar" and "tempereglar" (tempurature regulator) boxes were referred to as a radio amplifier. I believe this is not correct.

The third wire comes from the temp wheel and is for the A/C clutch switch. I located the wiring from the A/C relay and spliced in near there.

In the 240D the A/C Clutch switch and Aux Fan relays are connected (pin 3 to pin 4). On the 84 300d they are not. I cut pin 3 from the A/c clutch relay and spliced into pin 4 wire of the Aux Fan relay. Forgive my electrical ignorance in terminology... I was afraid to cut pin 4 wire as I noticed from the schematic that both relays would not have 12v switch source? -Need help with this... Would any electrical gurus know how to activate each relay with a switch??? I'm not confident in my wiring here. I sheared my pressure port in the A/C line tightening the 134a adapter fitting, so a/c test will have to wait in meantime.

As far as I can tell, you do not need to do anything with the harnesses that plugged into the CC head unit or tempurature regulator.

Another observation is I only have the highest blower setting. 1 and 2 do nothing, bad blower resistors?

Hope this helps

Zacharias · #3 04-05-2015, 01:03 PM

Quote:

Originally Posted by 84-300dee

Another observation is I only have the highest blower setting. 1 and 2 do nothing, bad blower resistors?

Which blower resistor pack did you use, the old "toaster" from the original system or the 'TV antenna" ACCI model (on the 240d I believe it's in the heater box?).

Is it the same blower motor being used in the new system?

84-300dee · #4 04-05-2015, 02:56 PM

I used the resistors from the 240d located at the top of the hvac box inlet accessed from under the center cowl when installed. They do look like toaster elements.

Actually the wiring for that was not touched as when I pulled the box I cut it from the main body harness to the left of the hvac unit. It's a part of the harness with a connector mounted to the box to the left of the evaporator lines on the passenger side of the box.

It works with either blower motor as I swapped them trying to troubleshoot.

I basically tried to graft the 240d system into my 300d wiring. I could not find any guidance to do this particular swap. Only people who have said they have done it, but either don't remember or can't tell me how. Hope this post can help others trying to do this.

My original type 3 auto cc has the weird resisters on the passenger wheel well.

84-300dee · #5 04-05-2015, 03:33 PM

Some pictures:

The original autocc rats nest

Connector where I tapped for power:

Close up (red w/yellow stripe):

The temperature regulator (left) and blower regulator (right) electronic boxes above the hvac box (300D)

Ran my boost gauge through the now vacant interior temp sensor hole.

Interior lighting was easy, cut the Christmas light string from the existing wiring and spliced the 240 lights in.

If I can't wire the ac and aux fan relays correctly, how can one wire a switch to activate them?

84-300dee · #6 04-14-2015, 10:50 AM

Ok, so my blower only works on High, in position I and II there is nothing.

Please, anyone who has done the swap. Did you get your A/C TO WORK??? Thanks

Zacharias · #7 04-14-2015, 11:09 AM

Have you looked at this?

300CD to 240D manual climate control conversion

It's for an earlier car, a '78 with the old ACC system, but it might have some useful info.

84-300dee · #8 04-14-2015, 02:04 PM

Quote:

Originally Posted by Zacharias

Have you looked at this?

300CD to 240D manual climate control conversion

It's for an earlier car, a '78 with the old ACC system, but it might have some useful info.

I did thank you. Both were the early versions of each system. early ACCII to early CCI (rotary A/C temp dial) vs. my late ACCII to late CCI (vertical A/C temp dial). The two schematics were markedly different (especially ACCII)

Or maybe they aren't, unfortunately, Electrical Schematics are very greek to me...

Best I can tell is that I need to splice/cut/add wires to the A/C Clutch and Aux Fan relays located in the black box on top of the drivers wheel well.

I have attached the schematics i'm working with for the electrical gurus.

Thanks for help in advance!

charmalu · #9 04-21-2015, 11:23 PM

Check out this thread, it might help you.

Manual Climate control swap

Charlie

84-300dee · #10 04-21-2015, 11:48 PM

Great link! Thanks

Yes, crazy4diesel was attempting the same swap. There was no final resolution and unfortunately, I've been unable to contact him... I will link this thread to his thread for more exposure.