Question about air compressor and A/C
 

My g/f's SL recently had it's A/C go out. It would work at first when she started it, then would stop working after a few minutes. After about a week of this it stopped working all together. It made a whirring sound when she had the a/c on that got worse when it accelerated. When she turned the a/c off, it went away all together. I checked the R134 pressure with a gauge and it was sufficient.

Several of my buddies and myself thought it was the air compressor. I took the old one off, bought another one and installed it. I tried to re-charge the system with R134 but it still just blows hot air, no cold air.

Now, I've heard several things as to why it's not working.
1) Anytime you change out the air compresser you have to replace the inline filter and drier as well.
2) To re-charge the system you have to pull a vacuum on it and oil the new compresser in order for it to work

The first doesn't make sense to me at all. The second I could understand as far as there needing to be a vacuum for the R134 to go into the system properly. Does either of these make sense or could it be something else I'm overlooking? Is it possible it's not the compressor and something else? (compressor did sound like a bearing was loose when pulled off) Any help would be greatly appreciated.