Loose belt-- "A/C belt" I think? HELP!

Hi,
One of the belts on my 1983 300D Mercedes is loose and wobbles wildly-- I am 99% sure its the belt that controls the A/C. It looks like the parts are all solid, just needs adjusting. I felt the tension on the
other two belts and they are firm, but the belt in question has quite a bit of give (about a 1/2 inch or so).
I couldn't find any previous postings on this.... Does anyone have experience tightening the A/C belt? Any help in how to do this and also in how tight it should be? It looks difficult to get to. Should it feel like the other two belts' tension?
Thanks, Kate
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The A/C compressor's drive belt should be well tensioned - about like the belt to the power steering pump.
One needs to loosen the bolts (probably three) that attach the compressor to its bracket but NOT the bolt that secures the pipes to the compressor.
My '80 has a tensioning screw with a small hex nut for a wrench, your car may differ. Start turning it while watching the belt so it is tensioned not made looser. I have to access the mounting bolts from underneath but the tensioner from the top.
When you're satisfied with the belt's tension - and don't be shy about tensioning it, the spec. is 1/4" deflection with a 13 lb push - tighten the compressor's mounting bolts (to about 40 ft lbs.)
Done.
Be sure to note how many mounting bolts get loosened so the same number are tightened.
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Turns out the problem was the screw that holds the AC unit down under the hood had jostled out and the entire thing was rattling. This ended up loosening the AC belt, but once I got it bolted down properly, the belt tension restored on its own. I replaced the 2$ screw from the hardware store (it was about 4" long), and the major rattle in my car has gone away!
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