Don't condemn the a/c system as being shot just yet. If you had a serious leak, it most likely wouldn't have held 110 psi while sitting untouched for two weeks. You need to make sure your compressor is coming on and cycling like it should. I'd imagine your summer days are a lot like mine so start it and set the a/c on max and after a few minutes your compressor will most likely stay on and your aux fan should kick on. You should at least see cooler than ambient temps. If it still feels warm, time to start checking things like whether or not the ccu is fully closing the monovalve, or possibly the monovalve itself. Check the compressor first to make sure its cycling properly.

If your belt was loose enough to be slapping around, it very well may have been slipping. It was posted somewhere on here that these compressors require somewhere in the neighborhood of 8hp and a loose belt can't transmit that. Don't condemn the compressor right away if you hear funny noises coming from it. Its not unheard of for the three 19mm mounting bolts to back out. Its happened to me and I've heard others talk about it.

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Seth

1984 300D 225K
1985 300D Donor body
1985 300D Turbo 165K. Totaled. Donor Engine. It runs!!!
1980 300SD 311K My New Baby.
1979 BMW 633csi 62K+++? Dead odo