450 SL Climate Control - PeachParts Mercedes-Benz Forum

jsjmb450sl · #1 08-09-2010, 12:56 PM

Would like to ask some help & guidance on my Climate Control. I've looked for previous threads but forgive me if this is already covered...and please redirect me.

I'd like to diagnose the system from start to finish. Current symptoms are it always blows hot (not good this time of year). I can move the temp wheel from one end of range to the other, and no change in always hot air. The vent controls (auto hi, lo, def, etc.) seem to work.

So I'd like to start with an overview of the system and some basic troubleshooting - identifying the components, (i.e. controls, sensors, blower (seems OK)) to make sure they are all there, and then some basic electrical checks. If I can get the climate control to run hot when thermostat is turned up, and un-heated when turned down, that would be great, and from there, I'll begin my exploration into the A/C side. But that's a more complicated system that I suspect hasn't been operating for a decade, so we'll hold off on that for now.

Thanks,

Stu

RadioTek · #2 08-10-2010, 12:43 AM

If you have what is known as ACCII (Automatic Climate Control vII) there is a known weakness in the climate control servo. They are known to fail often, one user on another board was going through rebuilt units in 12 to 18 months.

There is a modern replacement for that system that is much more robust: http://unwiredtools.com/accii.asp People have had excellent luck with them. I believe they are a bit more expensive than a rebuilt unit, but they make up for it in reliability. The install is supposed to be a nice Do It Yourself job, but can be 'farmed out' if necessary. The Tech Support for install is reputedly very good.

I can only give 'second hand' info, as mine has the older manual system. And it doesn't work either, but getting it working is going to be a major undertaking.

Good Luck
Scott

jsjmb450sl · #3 08-10-2010, 09:27 AM

Scott,

Thanks for the tip. Just following the link to the OEM replacement has been a big help for me. The part is a bit expensive, but the free installation manual has some great assets for my getting started whatever I decide to use. Pictures of the servo, sensing unit, servo pump, vacuum line configuration, and explanations of same are all a great help as I try to figure out just what this system is comprised of and how it is (or isn't) working.

Wondering at this point if there is some sort of state diagram or state table indicating what signals should be where under what conditions...might be help in diagnosing if the servo controller is in fact shot.

Anyway, I will continue poking around and will keep you posted. And I appreciate the support.

Stu

jsjmb450sl · #4 08-10-2010, 09:35 AM

Quote:

Originally Posted by jsjmb450sl

Scott,

Wondering at this point if there is some sort of state diagram or state table indicating what signals should be where under what conditions...might be help in diagnosing if the servo controller is in fact shot.

Stu

Of course the next link on the UT web page was a state table of the vacuum system. That will be some help, for sure.

S

meltedpanda · #5 08-10-2010, 11:08 AM

ACCII Climate Servo: 102 or 104

read here, great thread

jsjmb450sl · #6 08-10-2010, 12:08 PM

Quote:

Originally Posted by meltedpanda

ACCII Climate Servo: 102 or 104

read here, great thread

Wow. That will be a great help. Thanks very much!

S

jsjmb450sl · #7 08-18-2010, 10:37 PM

Simple stuff, but always nice to start on a good foot. Only had a little time tonight so I borrowed the UT instruction manual (thanks for the free download!) and used the thumbwheel verification instructions to test the resistor chain. Fashioned some simple jumpers of my own for the servo amp connector, and measured 3.6K and 2.29K Ohms at 85 and 65 degree settings, respectively.

Next will be to check out the servo amp to see if it responds appropriately, then the servo controller and vacuum lines themselves, I believe. Finally once I have the heating controls and operation verified I think I can then take on resurrecting the Air Conditioning side of the equation...

Slow progress is expected as my next real block of time will be to install the new Power Steering pump that arrived yesterday (Thanks Phil and Roy!).

More as it develops.

S

PS - Dumb question (maybe I can look it up) but should the resistance values behave the same with the jumpers removed and the servo amp installed as they did with the jumpers installed?