You said that you had freaon added, but what about a system leak check? The original freon had to go somewhere, since this is a closed system. I suspect the $150 dollars worth of freon went the same way as the original charge. The vacuum pump system and A/C are not connected, but it may have been agravated by the vacuum pump work, such as disturbing the lines and increasing the leakage rate, if it is/was a leaking line. Unless you see something really unusual, it is not the fault of the mechanic. Haver you confirmed the electric clutch is engaging when the A/C is selected? Maybe the fuse blew or the electric line to the compressor clutch got knocked off? Also, oil on the back of the compressor is a bad sign! Living in Texas, you will want A/C and I think that you will need a comprehesive fix. Probably, compressor, a line or two, receiver/dryer and freon again. It won't be cheap :-(

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Deezel
87 300TDT
150,000 miles