Replacing the ACC? - PeachParts Mercedes-Benz Forum

arew264 · #1 08-09-2007, 11:52 PM

This is an idea I've had percolating for quite some time.
It's not diesel specific, but this is the only forum I've been in, really.

Anyway, my thought is that you could replace the original ACC controller (from the 123, 124, 126, and any other cars with a similar system) with a small (low power) computer.
You might have to get some sort of display and input panel custom made, but if you found a company that sold minicomputers for applications like this that could operate or contained 12v relays (for both the switchover valves and the A/C), it could be used.
I'm not sure how you would get it to read from the temperature sensor, but something custom could be rigged there, if need be.
The fan would be more of a challenge. I'm not exactly sure how that controller works.
Any programming involved would be fairly trivial, you just get a set temperature, display it constantly (possibly along with the temperature from the cabin sensor), and calculate the difference. You could then use set thresholds to determine how to react.
For input, you need temperature up and down buttons, a mode button and fan speed buttons (to override the automatic control if need be), and an A/C switch to choose whether to signal the klima or not.

All this seems possible to me, (although a lot seems possible to me that is unrealistic). The problem would be finding a company in the business of making such things, because if you find one, chances are they are going to be dealing with situations much like this.

The best lead I have had so far for such a thing is Phidgets, a company that makes USB based input and output systems. They have quite a bit of this sort of thing, but USB doesn't appeal to me for this situation (although it would work), and you still have the problem of rigging some sort of computer at the core. It would make the programming much simpler though.

pawoSD · #2 08-10-2007, 06:32 AM

I also have thought of this, but it seems like it'd be a fair amount of work. My plan involved replacing the dash area with an LCD + computer in the car that could do: Satellite Radio, GPS, Climate Control Functions...rear interior lights, etc...etc....it'd be pretty awesome.

But I have no money or time for a project like that. I faintly recall a long time ago someone modded their entire switch/climate panel to be a touchscreen, but don't remember what they did with the climate and other controls....

pmckechnie · #3 08-10-2007, 07:25 AM

I also have been thinking about doing something like this using a Basic Stamp.
This is a microcontroler programed in the Basic language. I was thinking about using the original control panel but replacing the electronics. It would have to be a hobby type thing because it would require a lot of work and time. I just like doing things like this but the time is the hard part to find. Do a Google search on Basic Stamp and you will find that it is capable to doing such things and is not that expensive. I think it would be a good platform since it can be reprogrammed many time to work out the bugs as they come up. Let me know what you think and maybe we can get something started along these lines.

#4 08-10-2007, 09:06 AM

I'm sure it can be done, but I doubt it would be affordable. The correct ACCs are available for less than $300 rebuilt, and many folks still try to fix the old ones. You would have to sell these for about that price to have a market, and I don't know how big the actual market is. It would take a considerable amount of work to develop a working prototype, and a very considerable amount of money to develop a production model, I don't think the market is large enough to justify the time/cost.

rrgrassi · #5 08-10-2007, 10:12 AM

Good idea, but...it's another point of failure introduced. An Allen Bradley PLC runs about $700. Then you have to buy the software to configure it, and it does require a mini computer to run the PLC.

arew264 · #6 08-10-2007, 01:07 PM

Yea, there's the issue of cost. The electronics to run the relays and switchovers would cost like $200 without any sort of controller.

How does the fan speed controller work, anyway?
For everything else, you're putting 12v through the switchover valves, a 12v signal to the klima, but how do you regulate the blower? I know you have blower relays, but the speed?
Is there any other components I missed?

rrgrassi · #7 08-10-2007, 01:50 PM

Blower resistors.

#8 08-10-2007, 02:09 PM

Quote:

Originally Posted by arew264

Yea, there's the issue of cost. The electronics to run the relays and switchovers would cost like $200 without any sort of controller.

Actually, I was thinking of the $50K+ of development and tooling costs that would be required to bring a product like this to market. It only works if you are going to be able to sell several 1000 units with a $100 profit.

It might be practical to build a one-off unit for your car, but turning that into something that can be produced in volume requires a serious investment.

arew264 · #9 08-10-2007, 06:30 PM

I was never planning to try to mass produce something like this, there just aren't enough people to sell it to.
If I do end up doing this, I will post a fill how-to.
Anyway, the most cost effective solution seems to be pmckechnie's basic stamp. Here's what I'm guestimating would be needed:
(I should probably mention that I'm a high school student, so I have a miniscule budget for something like this)
Basic Stamp 2 (http://www.parallax.com/detail.asp?product_id=BS2-IC)
Programming Module (http://www.parallax.com/detail.asp?product_id=28150)
Thermocouple (http://www.parallax.com/detail.asp?product_id=800-00027)
Screen with buttons (http://www.parallax.com/detail.asp?product_id=29121)

Those would get the temperature and user input, I'm not sure how to deal with the blower (although I think I know how that works: see below) and switchover valves/klima signal (would you use a DC motor controller?).
As for the fan, when you say fan resistors, I'm assuming that that works because you can put 12v through one of 5 paths, four through resistors that provide varying resistance in order to get different speeds, and one path straight to the blower for full speed. Is this correct?

arew264 · #10 08-11-2007, 10:35 PM

-Bump-

Jeremy5848 · #11 08-11-2007, 10:57 PM

This is a clever idea. I agree that the "brains of the outfit" could be replaced with a BASIC Stamp and some driver transistors. You would have to develop a complete understanding of how the ACC works, reverse-engineer the electronics and create schematics, then design a Stamp program that would replicate the functions.

The factory's design actually works very well if all of the subassemblies are in good shape. There is far more intelligence in the system than we realize, complete with National Semiconductor COP microcontrollers (which I helped to build in the 1980s). It would be nice to find, perhaps in an old German technical magazine, an article from the early 1980s describing the development of the system and how it works.

We read many ACC tales of woe on this forum that are primarily due to bad PC boards, fried traces, malfunctioning Klima relays or monovalves, etc. Once all of these things are working properly, the system works well. (I will allow those who prefer a completely manual system to utter a single "Harrumpf!" at this point.)

Jeremy

arew264 · #12 08-11-2007, 11:05 PM

Yes, when it all works, it is quite nice, however, when the car starts getting this old, most of the time it doesn't, and when you want to manually override it (which I rarely do), this system does not lend itself.
I do admire that they had a system this complex and well thought out, but the fact is that it is now getting old and problematic (after trying to resolder some connections, I can no longer get it to turn off or to defrost), and a system that gave more information would be quite welcome to me. (it would be nice if we could get the set temp in Fahrenheit, the current temp as read, and the current blower speed in a more modern system)

veg_svc · #13 08-11-2007, 11:43 PM

A few years ago I started working on a digital dash assembly for an old '63 truck. I know, I know dakota digital. Plain and uninspired blue guages are not really appealing to me.

There is no reason that your Idea won't work, actually it is probably not all that difficult to achieve.

Draw a block diagram of what you want. Forget the design if the original controller. All you really need to know is what is being controlled and design a system to work the way you want it to.

You have some inputs "user temp" and "Temp Probe" and some outputs "compressor", Fan Speeds (5 total) etc.

There is no reason that the temp probe could not be changed to a more up to date unit and do away with the old one entirely. The basic stamp probably already has freeware that will provide the functionality you desire, also there are thousands of folks out there on the net that write routines all the time and are happy to share code.

I use 8051 with asm and also pascal but do have some basic programming knowledge. A basic stamp, a few transistors, some bias resistors, maybe a ADC for the temp probe and a display driver and you are in business.

Maybe start your project at the simplest place. Button input 1: Turn on compressor, Fan on (High) = Button input 2: Turn off compressor, fan off.

Once you have that other pieces can be built in as you have time.

a2t · #14 08-12-2007, 12:01 AM

I'd try to simplify the logic as much as possible. 3 fan speeds via blower motor resistor, manual temp settings. Ditch the feedback loops, who cares if ACC knows how fast your going, or if it suddenly changes from defrost to floor. Seems like a couple buttons would be enough for manual control of the thing. Its overly complicated as is.

My ACC seems to run AC 100% of time (which is fine by me, being that its 120F on the road in Atlanta during summer).

Ive fancied repl with a 3 way switch that reads : HOT, COLD, Off. Toggle as necessary. Maybe add 3 pot fan speed controller. Air comes out all vents when on.

Can you tell Im a mechanical engineer, with no respect for EE's

?

#15 08-12-2007, 12:17 AM

Quote:

Originally Posted by a2t

I'd try to simplify the logic as much as possible. 3 fan speeds via blower motor resistor, manual temp settings. Ditch the feedback loops, who cares if ACC knows how fast your going, or if it suddenly changes from defrost to floor. Seems like a couple buttons would be enough for manual control of the thing. Its overly complicated as is.

My ACC seems to run AC 100% of time (which is fine by me, being that its 120F on the road in Atlanta during summer).

Ive fancied repl with a 3 way switch that reads : HOT, COLD, Off. Toggle as necessary. Maybe add 3 pot fan speed controller. Air comes out all vents when on.

Can you tell Im a mechanical engineer, with no respect for EE's

?

What you've described is essential identical to the manual system in my 240D and it does work well. Personally, I prefer the ACC in my 300D because I don't have to keep playing with the silly thing, just set it and forget it. I almost never touch the settings on the ACC, it just works.

BTW, the AC is supposed to be on all the time for dehumidification (except for the economy setting).