Auto Air Conditioning & Heater Repair: Compressor really failed, or was it really a mechanical mistake?, pep boys, diagnostic check

Question
Well i have a 98' BMW and my A/C was blowing out hot air so i decided to go to Pep Boys and get the diagnostic check. They checked it and gave me a call telling me that the reason why it was blowing hot air was because a couple tubes were loose so they tightened it and then he said that now all i needed was the recharge so i gave them the go ahead to finish the work. Well i picked up my car and the A/C was blowing out cold air, and about 30 mins later it went warm again. I took it back and they ran another diagnostic check on it, that time they told me that the air compressor went out. He said that they just go out and didnt explain why, just that they get old. So my question is, from what you know on A/C is he really telling the truth and has info. to back it up (even though he didnt explain) or do you think that it was a mechanical fault?  

Answer
It is possible that the compressor just decided to cease at this particular time. It is also possible that they did NOT check to make sure that there was ny refrigerant oil in the compressor before they recharged it,. As the oil would leak out with the freon on a small leak and you MUST check the compressor for oil BEFORE you recharge the syatem.