help please

[andulinka]

HI, I have come here for help. I own chevy blazer 1995 and my AC stopped working, when i try to turn it on it makes such a horrible noise - squeal. I just paid 150 $ to Pep Boys to clean and recharge AC. They told me it's little bit noisy and it will need replace compressor someday. The day came about month later :-(. I found compressor on the net for about 150 $. Pep Boys want up to 750 $ for replacing compressor and recharging it with freon. I don't want to pay that much money. I was saving for road trip around US National Parks, I am gonna go after Labor Day, and I think I could use AC on the road. So I'd like to know if I can replace AC compressor with new one myself and then take it to a proffessionals to clean it and recharge it with freon. Does system must be free of freon before I try to replace compressor with another compressor? Are there any tricks? Anything i need to know before I do it? How should I do it? Please let me know your opinion, thank you so much Andrea