So I've owned this beautiful signal red 300SD for several years, and have not had the time and or money to give it the proper attention it deserves, but enough is enough and I'm finally able to get some projects going.

The first project is a wonky, slightly bypassed climate control system that gets heat and only heat. Each fan speed works as it should, not just defrost, so it seems the servo is at least partially functional. When I say its bypassed I'm talking about the fact that the coolant lines do not enter the servo, or the auxiliary water pump. I can also never hear the auxiliary pump running, though its still connected electrically. The servo also never makes any opening or closing sounds when turning the key on or off. I tested both directly off the battery and they both activate. The servo seems to open all the way and close all the way, at least from the sound of it, but only directly off the battery.

So why were these bypassed? Doesn't the fact that all the buttons function, from auto low to def mean the servo is somewhat functioning? The fact that is doesn't open or close when connected to its wire harness makes me think there's a problem with the amplifier. But if the amp wasn't working, wouldn't the functions that do work cease? Also does the amp control the aux water pump? If nothing else, I'd like the tie the aux pump back into the coolant system, as it does cool down a bit at idle.

I know this evil servo is a super common topic, but in all the reading I've done over the years, I've never found anyone with a bypassed servo that still had functional auto low auto hi and bi-level, as well as defrost.

I will say I only get heat, no temp control, or course that is probably because the servo is no longer tied into the coolant system, and can't regulate the flow. Before I had my current level of understanding of the system I thought the temp dial was broken.

Also does anyone know what controls the opening of the fresh air flap to the blower fan. I've wire tied mine open since thats the only way I get heat, and it barely opens when I turn the fan on any speed. Is is controlled via vacuum line from the servo?

Anyway I know this topic has really been beaten into the ground but as I said, I've read a lot about the servo and have never heard of my exact symptoms.

ok well I'll just go ahead and reply myself...

I've done some further testing of the electrical connections at the servo and the amp. Figured out that the servo is indeed the culprit for my battery drainage I've been meaning to diagnose for awhile now. Removing the 2.5amp glass fuse does make my test light go out. I then installed the fuse, as tested the plugs at the servo to figure out which one was pulling.

Now as most people have stated, the servo is known to cause power drains when its stuck and unable to close after turning the car off, and will simply keep trying to close until your battery dies. however, the pins responsible are the 4th and 5th, or green and black wires. Those wires however are not turning my test light on. The 3rd, or center purple wire which is supposedly a ground is lighting my test light.






I don't have a wiring diagram for the climate control so I'm unsure whether these are related directly, though I'd assume they are, the 4th (purple) wire from the right on the amplifier connector is also pulling power, and when connected to the amp, the 5th pin from the right also light my test lamp, but much dimmer than the 4th.

Just a FYI. The reason the fan speeds can work but not the coolant control is because the little plunger that opens and closes the coolant section can break off. The top part of the servo which controls fan speed would still function fine.

__________________
2004 F150 4.6L -My Daily
2007 Volvo XC70 -Wife's Daily
1998 Ford F150 -Rear ended
1989 J-spec 420SEL -passed onto its new keeper
1982 BMW 733i -fixed and traded for the 420SEL
2003 Volvo V70 5 Speed -scrapped
1997 E290 Turbo Diesel Wagon -traded for above
1992 BMW 525i -traded in
1990 Silver 300TE -hated the M103
1985 Grey 380SE Diesel Conversion, 2.47 rear end, ABS -Sold, really should have kept this one
1979 Silver 300D "The Silver Slug" -Sold

Give this thread a read from start to finish. It will show you how the servo functions internally. Very interesting.
Building an Evil Chrysler Servo

__________________
2004 F150 4.6L -My Daily
2007 Volvo XC70 -Wife's Daily
1998 Ford F150 -Rear ended
1989 J-spec 420SEL -passed onto its new keeper
1982 BMW 733i -fixed and traded for the 420SEL
2003 Volvo V70 5 Speed -scrapped
1997 E290 Turbo Diesel Wagon -traded for above
1992 BMW 525i -traded in
1990 Silver 300TE -hated the M103
1985 Grey 380SE Diesel Conversion, 2.47 rear end, ABS -Sold, really should have kept this one
1979 Silver 300D "The Silver Slug" -Sold

Thanks dude. While the mechanism inside that opens and closes may have broken, the issue at hand is, why does it not attempt to open or close it when the car runs or turns off? The fact that I was able to hotwire the servo direct to the battery and hear it open and close, yet never makes a sound when connected to the car should point towards a problem in the system before the servo, like the amplifier.

I removed and re-soldered the amplifier tonight, though I'm currently unable to test the results as my battery was too drained to start. Though the middle purple wire in the servo photo above is still lighting my test lamp, and I'll repeat that its supposedly a ground wire.