Newbie - 79 MB 300 CD - Mercedes-Benz Forum

 
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post #1 of 8 (permalink) Old 09-18-2006, 10:00 AM Thread Starter
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Newbie - 79 MB 300 CD

Hello All,

I recently purchased 79 300 CD - it runs great and very comfortable - after the 1st week of driving the - what looks new - battery died. I had the alternator tested and they determined it had to be replaced - that was done a week ago. Car started fine all week - then on SUN the battery was dead again. Any suggestion on what to check next?

Perplexed in Santa Fe, NM

Thanks...
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post #2 of 8 (permalink) Old 09-18-2006, 11:05 AM
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Something is remaining on. Maybe the rear dome light? it has a seperate switch on the dash. glow plug relay stuck? It needs to be tested for a battery draw. Its a simple test. Any good auto electric shop can do it.
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post #3 of 8 (permalink) Old 09-18-2006, 12:23 PM
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A bad ACC Servo can suck the life out of a battery in a few days time.

"If spending money you don't have is the height of stupidity, borrowing money to give it away is the height of insanity." -- anon
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post #4 of 8 (permalink) Old 09-18-2006, 12:57 PM Thread Starter
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Thank you for the info... But may I ask what the ACC Servo does?

Grateful,

.a.
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post #5 of 8 (permalink) Old 09-18-2006, 01:29 PM
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It's a black plastic thing about half the size of a football. Lots of vacuum connections and four water hoses -- it's your car's version of a heater control valve.

"If spending money you don't have is the height of stupidity, borrowing money to give it away is the height of insanity." -- anon
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post #6 of 8 (permalink) Old 09-19-2006, 05:31 AM
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Did you simply try cleaning the connectors on the battery and removing rust/acid. This worked for my car. Check the voltage at the battery with all electrical on. Should still be around 14V. If it is less, the battery will discharge over time. Also check the acid in the battery, make sure there is enough. good luck.
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post #7 of 8 (permalink) Old 09-19-2006, 09:03 AM
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I'm sure that was all done when took the car in and had his alternator swapped out...

"If spending money you don't have is the height of stupidity, borrowing money to give it away is the height of insanity." -- anon
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post #8 of 8 (permalink) Old 09-24-2006, 10:52 AM
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I concur with GermanStar. You appear to have a key off current drain and it is most likely the servo. You can run a current drain test by dicsonnecting the negative terminal and connecting a one ohm ten watt resistor between the post and terminal. Check the voltage drop across the resistor with a DVOM. You should not exceed .05 volts. You can start removing consummers starting eith the servo until the meter drops below .05 volts. Good luck.
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