You would need the A/C to be operational for your defroster to work, since the A/C decreases the humidity in the passenger cabin which causes your windows to fog up. You would need to jack up the temperature to achieve the same effect without A/C operating. So I think you should get your A/C fixed.

In terms of your windshield wiper, you must have the single arm wiper common to all W124's. I've always found the wiper to be very good, even in the worst of weathers. Maybe the plastic blade needs to be replaced. If after replacing the blade you still find the wiper insufficient, you might wanna invest in a bottle of Rain-X, which is a pleasure to drive with especially on the highway or any other stretch of road where you can drive 60kph+.

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-= 1995 Mercedes-Benz E420 (W124 - Black Pearl/Black) =-