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flyloki 11-16-2003 03:48 PM

ACC Electrical Circuit Problem
1985 300TD

Driving down the road with heater on - the seatbelt light flashed on and off, at the same time the ACC fan slowed then came back on. Now ACC unit is acting a bit flakey. Fan and vent servos seem to work normally but I'm only getting heat.

Checked fuse box and the fuse for the monovalve, back up lights, horn etc is blown. Had recently put a hitch on car and done a few spotwelds w/o disconnecting battery. Could this have shorted the circuit through back up light ground or similar?

Where to check first? I will look at the ACC board tonight but is there any other fuse that could be blown taking out the circuit?

Thanks for any help-


95300YDT-A 11-17-2003 02:58 AM


Welding without disconnecting the battery. That against all odd's !
I would be very surprised if your A/C board wouldn't be shot, at least some electronical parts in it !


flyloki 11-17-2003 10:21 AM

Re: Welding

I know, I know. I said the same thing to my buddy who was doing the welding (an ex MB tech no less!) and he was like "should be fine way back here". :rolleyes

Would bad AC board also take out reverse lights?

flyloki 11-19-2003 12:51 PM

For future reference....
OK everyone, all together now---CHECK YOUR FUSES

or better yet


If you have the bullet style it more than likely they will be at least 20 years old. Number 14 had a little crack that was too small to see and was causing the problem. It's cheap insurance and often overlooked or causing unseen problems.


MrCjames 11-19-2003 05:11 PM

As good practice one might consider replacing ceramic fuses every 5 years. I was/am in the habit of replacing them whenever I perform a 90-k service!

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