The first thing that I would check is the function of the cabin air temperature sensor located in sunroof/dome light switch. LarryBible suggests holding a small piece of paper (.25" square maybe) up to it to see if it will hold the paper (ie, air being sucked into it)

A non- or malfunctioning cabin air temp sensor would cause your CC unit to do wacky things like blow too much or all the time.

First off I must say that the Mercedes Auto AC is a complicated system that being said it is equally expensive and time consuming to repair. Who really needs "Auto Air" . I WANT AC THAT RESPONDS TO MY NEEDS and not a $500 - $2000.00 repair bill every 2 - 5 years and I’m sure many others don't want that either. I repaired the AC in my benz doing the work myself and spent over $300.00 for parts and hours studing schematics and components. I repaired my BMW AC for less than $100.00 It needed twice as much work due to previous owners neglect but was much easier to repair.

The solution if well thought out can be quite simple. Most AC controls for most vehicles simply turn on a compressor and let you control the blower speed and air mixture.

I typically do not do things "HALF ASS". I have solved many applications for factories and companies all over the world for the past 10 years in factory automation, web control and automated packaging to name a few and have designed and built several machines worth over $500,000.00. I have redesigned many systems for CNC machines that were too complex and too expensive to repair. For example; a failed power supply. 750.00 to replace OE I did it for 29.95 and works just as good if not better with added surge suppression that I incorporated.

I know what I am doing and I always try to think of the best solution for the investment return as well as long term safety and reliability.

I do appreciate your input no matter how negative it might be. I have taken apart my Climate Controller, AC relay used a scope and voltmeter to diagnose my problems and have even reversed engineered the AC relay. I have spent many hours studying the MB Auto AC system and find it too complex for the simple operation it does. It's a "cool" (no pun intended) system and for the MB diehards that want all OE maybe its not for them. But for the others out there that just want their AC to Work, like myself, I think I can come up with a solution.


If I can come up with a simple safe inexpensive solution I believe MB owners will beat a path to my door. It sounds like a challenge to me and I love challenges.

Again thank you again Craig, duxthe1 and skiier3_9 for your posts!

Anthony Bridges

Something like this:

http://catalog.peachparts.com/item.wws?catpk=&sku=227550999

my auto mode works. I can hear and feels fan speed when it reaches desired temp. BUT if I want to keep fan in medium setting, thats what I want and its not for my climate control to choose it. MB auto climate control is very well designed but I never used it. I just want to have medium fan setting. If you can provide some details how to modify climate control unit please let us know. Hope this moment will happen soon. Keep up great work.
Thnak you
Victor

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1999 ML430 Silver 135k ml
Smoked LED taillights, Alpine in-dash DVD player, 12" sub, Pioneer components, 2 amps, 4200k HIDs, ML55 headlights, 20" rims, mirror LED blinkers

SOLD. 1996 E320 145k ml. Burgundy

SOLD but miss it everyday 1992 500sel Black
Chime buzzer mod,Alpine CD/MP3 player with stock amp,Euro headlights,S600 grill,20" rims, BEST CAR EVER!

SOLD. 1990 300E White
187k ml,smoked tails,Euro headlights,17rims,Intake,12" sub in first aid kit,alarm/autostart,buzzer mod

The easiest way would be to sacrifice the low speed switch, change the blower resistor for that speed to a smaller value and then the fan would run faster when you select that speed. You;d have to experiment with different resistor values to get the one you want, or just put a wirewound pot in place of the resistor, and when you get the speed you like, measure the resistance of the pot and then replace the old resistor with that value.

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Theo

1985 300D turbo 235K miles, Delvac 1, mostly B20 BioDiesel

klakka klakka klakka klakka...Arf arf arf arf...
How does that dog always know when Theo's home??!

It is going to take mw a better part of a week to finish this project.

I have 2 modification ideas.

W124 climate control blower motor modification.

1. Using the fader control position to install a variable resistor for infinite speed control. Both mods will only work on climate control systems that are working. This will not make your fan work if it is not currently working nor will it correct improper vent or heating/cooling operations.

2. Sacrificing the Auto button for a medium speed or include a small switch that will allow both that can be installed in glove box or under dash..

I would expect a cost of around $20.00 - $30.00 for a full color instruction manual or CD with lots of pictures along with all the components needed to do this modification.

What do you think ?tgantos , Victor300E

I don't know about using the auto position. It's a different circuit, and very complicated/convoluted from my first glance at the schematic. I would not want to have a solution requiring a complete redesign of the present pre-cmos logic. So I still think using the low speed position is probably your best option, but like I said I just glanced at the schematic. Now if you want to redesign the whole system and build a new controller for everything, using modern electronics, then you may have a market if you can get the price down around $300.

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Theo

1985 300D turbo 235K miles, Delvac 1, mostly B20 BioDiesel

klakka klakka klakka klakka...Arf arf arf arf...
How does that dog always know when Theo's home??!

Have you a solution Anthony with the anemic low fan speed on the 124??
The other issue on this terrible MB climate system is the one heat setting fits all on defrost. I have to continuously switch on and off to regulate the temperature in the cabin when defrost is switchted on.
Thanks - Tom

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'96 C220 138,000mi, '95 E300D 239,000 mi., '87 300TD 214,000mi '88 6.2 Turbo Diesel Chevy Conversion Van 253,000 mi.