So I have been reading here for about the last 6 months since I bought my first MB. I was lucky to find a 2 owner, 1984 300D here with 98,000 miles on it for about $3,300. The car was in good shape with the exception of little to no maintenance other than oil changes for the last 40,000 miles.
So I set out to do everything right and make it a clean, reliable daily driver. I started out by changing all the oil, filters transmission fluid, filter, motor mounts, air cleaner, etc.
All of this complete about 2 months ago, I also changed out all the fuses as they were a mix of copper, brass and aluminum types, all looked old. I read here to use the brass type, not the aluminum. So I ordered a number of the Bussmann BP/GBC types in 8, 16 & 25 amp.
I removed all the old fuses and kept the copper/brass ones as spares, threw away the aluminum ones. I then cleaned every fuse holder and installed all new brass fuses of the correct rating in every holder, checking that they were seated correctly and the holders were tight. All is good!
Fast-forward to this week, my A/C has been working on & off (terrible in 105F weather). So I am troubleshooting per thread recommendations here. I evacuate all the refrigerant, replace all o-rings and flush the condenser & evaporator. Still working intermittently. I find no leaks and my charge is still good - evacuated, weighed & re-charged yesterday.
So tonight, I read about the Klima relay, accumulator/drier pressure switch and temperature switch. Test both and they are fine. Look for Klima relay and can't find one... Look in the fuse box and find this scary scene:
Yep, that new fuse overheated without melting the element and got hot enough to melt/shrink the body material. It was collapsed enough that once I broke it free, it could bounce around in the holder. No wonder my A/C was going in and out. Anyway, I am glad this thing didn't somehow start a fire. Left to right is the burnt Bussmann, a new Bussmann and the older one I will use instead:
So to fix this issue, I took green abrasive and cleaned all the soot off each side of the fuse holder in question. I then installed a clean, good fuse and measured across the holder...7 Ohms - not good! I scrubbed more and more and then applied some No-Ox A special grease to the fuse and holder (this is what is used on the contacts of power circuit breakers, to keep corrosion at bay). I seated and re-checked the fuse, 0.4 Ohms - Good!
Here is how to check the fuse across the holder to ensure good contact:
So now I will try it out tomorrow and check the fuse once I am back home. I will update this thread if I find out some other issue was causing this overcurrent condition or if it was just due to the old fuse having poor contact.
Thanks all. Hope this helps out someone, I have gotten lots of help from the forum already.