Pics?

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I'm not a doctor, but I'll have a look.

'85 300SD 245k
'87 300SDL 251k
'90 300SEL 326k

Six others from BMW, GM, and Ford.

Liberty will not descend to a people; a people must raise themselves to liberty.[/IMG]

I have a 1980 300sd too and had the same problem. It was the trunk light switch. I took out the bulb and no more problems. Will replace the switch someday.

My 1977 240d had the same problem and same cure.

Checked the trunk light switch just for good measure, DCM, and it seems to be working correctly. I let her sit the whole weekend with the servo unplugged and the battery was still at full charge. What is odd is that I started the car and the AC came on. Got out and checked and the servo was definitely unplugged (see attached). Are there more that two plugs? Does it matter what position the system is in when you unplug it, because when I unplugged the first time, I had no AC?? Somebody tell me what I'm missing! I don't want to spend major $$$ on the wrong part....

Attached Thumbnails

 

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TClanton
1980 450SL 90K
1980 300SD 112K

I didn't unplug the upper thing that looks like a plug because the wires look like the are soldered in.....should that one be unplugged, too? Is my test crapped because I didn't? Man....

Thanks!
TC

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TClanton
1980 450SL 90K
1980 300SD 112K

The servo fuse is the inline fuse inside the fuse box, it is not on the regular fuse panel. I had this problem as well. (mine is a 6.9, I assume your car is the same).

If you test each fuse with the ampmeter as per previous suggestions, you will see the drain. For a battery to drain overnight, it must be big, almost like a headlight. Since it is not a headlight, it might be a short to ground which could be hell to track down.

When buying the parts, avoid the guy in San Diego (Can't remember his name). On Ebay he went by BigBabboo for a while. There are some threads here about him and what a nut case he is. I would get one from George Murphy.

I can't find the link now but a company makes an electronic replacement for the ACC system.

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MB-less

Emmerich- It usually takes 2 days or so (shortest time I've experienced anyway) before it is dead. At least it was 2 days before I tried to start the car and found it dead. At any rate, my indy indicated I should just unplug at the servo. The manual shows the upper plug as something to do with vacuum and the lower two as electrical. I just unplugged the lower 2. Guess I was hoping for an easy, even if expensive answer, without digging into electrical too much. It's too hot in AL to spend much time under the hood!

So you did have a similar prob with the servo on your 6.9?

Thanks!
Terry

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TClanton
1980 450SL 90K
1980 300SD 112K

OK. Looks like we're down to the servo. Had some private message help that was great...thanks again! One last mystery....should the AC continue to work even with the servo unplugged?? Does it just stay "parked" in the position it was in when unplugged and continue to provide air from that position until it gets juice again?

Thanks
TC

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TClanton
1980 450SL 90K
1980 300SD 112K

bingo!

I am guessing you couldn't switch over to heat today, not that you'd want to, but your servo is stopped in a position that allows AC to happen.

You probably won't be able to change anything from the push button unit, but if you have AC you are probably happy. You might be able to get to DEF since that runs independent of the servo. I wouldn't experiment, though. If you selected DEF and then tried to get back, the flap that diverts air to the windshield in DEF wouldn't close to direct air to center vents now because you have the servo unplugged.

Until heat is needed, you are probably all right.

I have a metal servo now and we'll see how well it holds up this winter. My two earlier plastic bodied servos cracked in about the same place. A mechanic told me they usually fail in winter when the fluid expansion around a freeze causes the bodies to break.

There is a lot going on in servoland and I have looked for help from experts who are sometimes baffled by the system.

hope this gets through. i couldn't post yesterday

one more thing.

i think it attaches to the servo mount.
it is the aux. water pump.

black and silver cylindrical thing. to the left in your posted picture

you can unplug it until you are certain it is working right. when (not if) it fails, it will take out the underdash CC amplifier which is the easiest thing you will ever replace on this car, but it is not cheap at around $100.

the aux water pumps can be rebuilt and they cost over 100 new.

the aux water pump works to circulate coolant to the heater core when the main water pump is not circulating much fluid like when the car is idling.

mine is unplugged right now. when heat season comes back I will have to figure out whether it must be plugged in for heat to come on. I don't think it has to, but the system is complicated and there are lots of things that are interrelated. one link out of the chain and the whole thing acts up.

right now I have my tire gauge stuck in the central vent flap to allow air through. it's a vacuum issue that will be easier to track down when the weather gets cooler here in Houston.

you don't need it (aux. water pump) connected right now in AC weather anyhow.

Thanks, Oxy! You should have heard a huge sigh of relief....a new servo wasn't in the budget this month, so knowing I can have AC for 10-12 weeks is great...

So you think I should go ahead and unplug the aux water pump until I get the new servo? Is there a plug directly to it, or an inline fuse? I'll look when I get home..

Thanks again for the major relief!

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TClanton
1980 450SL 90K
1980 300SD 112K

I don't think getting a new servo is the contigency for unplugging the pump. I would do it as a precaution until you can be assured the pump is working right and not frying your CC amp.

If you look around, there's a 2 prong plug connector harness going to the aux. pump.

if you put 12 volts to it and it turns, you are closer to where you want to be.

there is some spec for how many amps it should pull and that's where you have to be sure a working pump isn't going to fry the CC amp. i can't recall the spec but it has been mentioned on this board before.

maybe when it gets cold you can plug the servo back in, set your temp wheel to warm, get it just right and then unplug it again to disable in heat mode.

That won't give you the "A" in "ACC" but maybe you can get through a season or two before getting it all squared away.

it should cool off in Houston



in November

OK. I'll check it out and see. Thanks again for the help! Oh, and for the manual link. I'm going to print it and study a little more.....not that I will really understand it....

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TClanton
1980 450SL 90K
1980 300SD 112K