450SL AC Servo Issue - PeachParts Mercedes-Benz Forum

ArgeMan · #1 01-25-2006, 09:28 PM

Hi all. I've got a little cimate control issue going on in my 1980 450 SL. I purchased a couple of used servos from a salvage yard, luckily with guarantees that they will work or money back, hoping it's an easy fix.

I just finished replacing my cracked servo but see no improvement in the performance of system. The only thing that works is the defrost setting where cold air comes out. No air comes out of middle vents when Auto Hi or Lo or bi-level is selected.

When taking off my old servo, I unscrewed the bottom portion (with the 2 vacuum lines) - then I unscrewed the bottom of the replacement part but broke one of the screws, so only one screw works but I think I got a good seal on the tiny gasket when I screwed one of the two screws back to my old bottom portion of the replacement servo. I also don't have a screw on the vacuum block but think I'm getting good contact between the block and the servo. I hear the gears turning in the servo when I turn the ignition on.

Any idea what my next step should be since there's no change in the performance of the system? I have the feeling someone is going to say I might need a replacement AC amplifier. I know George Murphy sells both new and refurbished amplifiers as well as the rebuilt servos, so that's an option. Beyond that, I don't know what to do. I'm stuck.

Any feedback is greatly appreciated.

Regards.

Max.

jr811 · #2 01-25-2006, 10:44 PM

Try 79 450SL climite control fix under search

hopes this helps Jim

utnj · #3 01-27-2006, 05:55 PM

Phil at FastLane carries our digital replacement kits. Being the manufacturer of the kit and the forum sponsor here, I am certainly a bit biased towards our solution - but thought you might like to know about it.

The big culprit in these systems is often vacuum problems. We have detailed vacuum diagrams on our site - look under the support section/ACCII for links to the vacuum diagrams with and without our kit installed. You may also find our other documentation helpful in better understanding the operation of the ACCII system.

You can learn more about our solution and find the relevant documentation at http://unwiredtools.com. Click on ACCII under the products section.

You can find the kit on FastLane by searching special order parts : Part Number ACC2G04

Frank

UnwiredTools, LLC
fableson@unwiredtools.com
http://unwiredtools.com

Richard Wooldridge · #4 01-29-2006, 03:45 PM

Hi there,
I second utnj's suggestion to go to his site and download his vacuum diagrams, they were very helpful in locating vacuum leaks in my '79 SL's system. One thing he doesn't mention but I found wrong was the one way valve (Blue body, black end) that is under the hood on the driver's side of the car next to the hinge. On my car it was hardly passing any air, so the vacuum level in the entire climate control system was low. Also, I ordered some 3 way and 4 way rubber vacuum connectors from Performance products, and replaced all the ones I could find, as they were getting hard and leaky. If you don't have enough vacuum to your main switch (Sw 19) the fan won't work in Auto lo, Auto Hi or Bi-level positions. It takes around 175 mbar of vacuum to close this switch, and it is in series with the fan motor. In the Defrost position the switch is bypassed by a relay contact on relay 18. That connector on the bottom of the control unit with the two vacuum lines you mentioned in your post is a thermostatic switch that only allows the compressor clutch to operate after the engine temperature has reached at least 40 degrees centigrade, or around 105 degrees F, so if you don't care if your compressor operates at a lower temperature, you could just bypass the thing entirely.

By the way, I purchased and installed one of the Unwired tools kits, and it works just fine after I fixed my vacuum leaks and fixed a crimping error on the +12v line at one of their connectors. They offered to replace the unit, but I had already fixed it. I recommend their kit as a very good fix for a poorly designed original control unit.

Regards,
Richard Wooldridge
'82 300D/4.3L V6/T700R4 engine/tranny swap
'79 450SL
'75 280C

ctaylor738 · #5 01-30-2006, 07:32 AM

Sounds to me like you got another dead servo.

Is the fuse OK? Can you hear it move to "Park" position when you turn the ignition off?

Beyond that, there are some basic tests that you can run to see if your servo is alive. George Murphy (george_murphy@compuserve.com) sells a very good troubleshooting guide for $5.

ArgeMan · #6 01-30-2006, 07:47 AM

Thanks for the feedback. I am awaiting George's troubleshooting guide. The servo is working, as far as I can tell (I hear it running and I get hot air on defrost setting). I have a vacuum leak somewhere.

I'm wondering now where to get patches for the vacuum lines - Performance products or unwired tools? Is there a "repair kit" for this? I figured it would be as easy as splicing out the punctured line and putting in a connector (or additional line) to replace the leak.

Feel free to share you experience with replacing lines (or connectors).

By the way Richard, how do you bypass the thermo. switch? Is this an electrical or vacuum line? I'm guessing you splice the lines together.

Regards.

Max.

Richard Wooldridge · #7 01-30-2006, 09:26 AM

Hi there,
It is a vacuum line, just take a piece of plastic line and plug the two rubber hoses into it. This will allow vacuum to reach switches 20 and 19 whenever the climate control is set to anything other than the off position.
I had to do quite a bit of rework to revive the heating in my 450SL. I bought the car on Ebay from a dealer in Fort Lauderdale, FL, and apparently the heater had not been working for several years or more - the control unit was all corroded, the gears and drive to the valve were completely corroded away! (I found that the heater didn't work when I was driving the car home to Washington State from Florida, when I got to Eastland, Texas it was 23 degrees, and NO heat! The AC worked great, though!) Also, the vacuum plug that plugs to the top of the control unit had hardened up and the lines were very leaky where they plugged onto the control unit. When I installed the digital servo replacement I ended up removing all that, just have 4 vacuum lines coming through the firewall now that connect to some new vacuum solenoid valves that are operated by the digital servo control unit. What I did was find another donor car in a yard and I stripped out all the vacuum lines I could, ended up replacing much of the vacuum system. The digital servo upgrade simplifies the vacuum setup, and I redid the vacuum lines wherever I could because the Y and cross rubber connectors were all hard and leaky where the hard plastic lines plugged into them. I also replaced the pushbutton switch and the group of lines that plug into it with the one from the donor car as it was in much better shape. I think my car was parked in a hot place a lot to make those lines go bad.
I ended up using a mity-vac to check all the vacuum elemnets and switches for leaks, and found many. It only takes one leak to kill the heater operation! All the vacuum to the climate control unit goes through tiny holes in the push button vacuum switch (around .030!) so it doesn't take much of a leak to cause the system to fail. I borrowed a factory manual and used it in conjunction with the Unwired tools downloaded vacuum charts, which I found much easier to read. The ACII climate control is amazingly complicated and hard to service since it uses vacuum to control both vacuum and electrical switches AND a differential amplifier to run a motor that operates both the heater valve AND a vacuum switch AND electrical switches that control the fan speed. It took me a lot of evenings reading the factory manual's ACII section before I really understood the function of most of the pieces of the system. (Still don't understand the function of Relay 13 - something to do with the AC system.)

Regards,
Richard Wooldridge
'82 300D/4.3L V6/T700R4 conversion
'79 450SL
'75 280C

Richard Wooldridge · #8 01-30-2006, 11:27 AM

Hi again,
If the temperature adjust knob will control your heat in the defrost mode, your servo and amplifier are working ok. You just have a vacuum leak that is preventing switch 19 from operating. On the 107, switch 19 is the one at the far right side above the passenger footwell. It has a green coded vacuum line to it. You should be able to make the blower come on in auto lo, auto hi, or bi-level by applying a vacuum source, such as sucking on a hose, to switch 19. If the blower comes on, find the leak. NOTE that your control unit's vacuum control switch could be the source. On my car both the defrost actuator and the footwell actuator were leaking, along with the big plug at the control unit. You can temporarily plug the lines to a leaking actuator to get the rest of the system working.

Regards,
Richard Wooldridge
'82 300D/4.3L V6/T700R4 conversion
'79 450SL
'75 280C

ArgeMan · #9 01-30-2006, 05:04 PM

Richard - great advise - Your drive from FL to WA must have been an awesome one - I hope you had the chance to take the top off and enjoy the fresh air from time to time...

I'm going to do what you recommend. Study the system, look at Unwired Tools' diagrams and find my vacuum leaks...

Thanks Again.

Max.

ArgeMan · #10 01-31-2006, 06:13 PM

Update on ACII status:
1) Dowloaded ACII diagram from unwired tools - these are very user friendly once you study it and figure out what symbols mean
2) bypassed thermo switch by connecting yellow and black lines together - this is recommend for those of us living in areas were we want the AC to turn on immediately - drawback, heat comes on immediately (blowing cold air in winter unless you run car for a while)
3) tested positive switch 14 (19 in other cars and unwired tool's diagram) - ac blower comes on when i create vacuum at switch
3) have begun testing lines for vacuum leak - start at vacuum source and test my way down each line to single out leak
4) I am awaiting replacement from performance products for broken blue/black check valve by engine on driver's side - I may have broken it myself when checking connection here

I have to thank Richard for lending me his precious time and the incredible guys at unwired tools. Both have taugh me loads so far.

Richard Wooldridge · #11 02-07-2006, 02:30 PM

Hi there,
I'm interested to know how you are doing with your climate control system! Can you give us another update? I know you have made more progress since the last communication...

Regards,
Richard Wooldridge
'82 300D/4.3L V6/T700R4 conversion
'79 450SL
'75 280C

ArgeMan · #12 02-07-2006, 05:50 PM

I am happy to report that I tracked down the vacuum leak to the passenger's side main air flap actuator (double element # 44). My local dealer had the part for $110 while George Murphy sells them for approx. $45 - can't beat this deal.

Only in the end did I realize I was going about it backwards. I started tracking the vacuum leak at the lines, something that took me hours to do, when instead I should have started at the weaker diaphragms of the actuators, these I could have tested in minutes and ruled out first.

All in all, I had a great time working on my car and take pride in doing the work myself. My mentors Richard W. and George M. were so nice to answer my questions, I just hope I can help someone out and give back to the MB karmic account

Regards.

Max.