1980 300SD - ACC Servo?? - Benzworld.org - Mercedes-Benz Discussion Forum

benzconvert · 09-20-2009, 04:34 PM

Just bought a 1980 300SD. Previous owner ran a line from the compressor switch to run compressor when defrost button pressed. I removed the dash and replaced the bad center pod. I see the pods open and close depending on which buttons are pressed. The compressor engages and pod opens when Lo-AC button is pressed but the blower doesn't engage, only with defrost. Same with high and bi-level. Any ideas? Also can anyone point me to where I can get that dreaded push nuts(I don't know the name) that secures the vacuum pods? I damaged several and don't feel confident that they will stay put when I reinstall the dash.

Thanks,
david

jdroberson · 10-06-2009, 12:36 PM

There could be a vacuum or a blower motor issue. The switch to turn the blower on is vacuum controlled, so the blower won’t get power until the car’s been running for a few seconds, assuming the ACC and vacuum system’s working right. When you’re ready to test, be sure there’s vacuum to work with (run the car for a while and then turn it off).

See if the blower’s getting power to it by disconnecting the plug on the blower and test for 12v when it should be blowing. If it has power when it should and doesn’t blow, then you probably just need to replace the brushes in the motor. This is not that tough to do. There are some walkthroughs online. I recently did this because my blower would work on defrost but not on low. There just wasn’t enough juice on low to spin the fan given the worn out brushes.

If you’re not getting power to the blower when you should be getting it, then you’re looking at a different issue and I can’t speak to the stock ACC because I replaced mine with the unwired tools upgrade due to a coolant leak when I bought 79 300SD. I also don't have experience with the pods

benzconvert · 10-06-2009, 05:26 PM

Thank you for the reply. The blower runs like crazy in defrost but not anywhere else. I am going over the wiring diagrams with my mityvac in hand, then I am going over the electrical. I did notice when I put a jumper on the compressor and blower it cooled great, also the amplifier was getting pretty warm, is that normal?

jdroberson · 10-06-2009, 05:58 PM

part of the ACCII upgrade I did was to remove the amplifier, so I didn't have much time with it in the car, but remember thinking it was hot when I removed it.

benzconvert · 10-06-2009, 06:40 PM

Thanks Nestorb98. How did the installation and use of the system you bought? Looks great in pictures, is it performing how you expected?

benzconvert · 10-11-2009, 07:26 PM

Quote:

Originally Posted by benzconvert

Just bought a 1980 300SD. Previous owner ran a line from the compressor switch to run compressor when defrost button pressed. I removed the dash and replaced the bad center pod. I see the pods open and close depending on which buttons are pressed. The compressor engages and pod opens when Lo-AC button is pressed but the blower doesn't engage, only with defrost. Same with high and bi-level. Any ideas? Also can anyone point me to where I can get that dreaded push nuts(I don't know the name) that secures the vacuum pods? I damaged several and don't feel confident that they will stay put when I reinstall the dash.

Thanks,
david

I just had my servo rebuilt by George Murphy. After cleaning up some vacuum leaks, I have lo, hi, bi-level, and defrost. I suspect more vacuum leaks but the worst is don't have any vacuum on the white line that comes from the servo and opens the center vents. Also I have vacuum on the line to the compressor switch but it doesn't engage the compressor. Any ideas? Thanks,