Need advice on A/C repair.

Need advice on A/C repair.

Hey guys! I've been having some issue with my 2007 335's A/C for the past 2 years. It started with warm air coming through half of the vents and cold air out the other half. After checking in this forum I learned that that happens when you're low on refrigerant and that I probably have a leak. So for the short term, I picked up a can of the A/C Pro refrigerant that comes with the low pressure gauge and I gave it some charge. Well that seemed to do the job and for a while everything seemed ok for about a year.

Well this year I started noticing a whirring noise that would change in pitch based off of engine rpm that I could especially hear when the rpm's are low. I gave the system a little more charge but that didn't do anything to remedy the sound. I did some more research and found that it could be the compressor wheel bearings or the system may be low on lubricant. Knowing that the cheaper of the 2 issues to fix was the lubricant, I ordered a set of coupler adapters for an old manifold gauge set i got from my dad. I also picked up a charge can of PAG 46 oil from autozone that contained 3oz of fluid ( 1 oz pag 46 oil, 1 oz 134a refrigerant, 1 oz ac line conditioner).

Yesterday I got to work. I connected to manifold set to my high and low lines. I burped the lines of the gauges to make sure I wasn't introducing any air into the system. Connected and added all of the charge can to the system. Cleaned up and made sure everything was running ok. I then ran the a/c for 20 minutes and found that the whirring noise went away .

The next day I started up my car and the noise was still gone. Butt... after driving around for an hour the noise started coming back. It still is a lot quieter than it was last week. So I guess I've got more work to do... So in figuring out next steps I went ahead and added some UV dye to help locate a leak. So moving forward, I've got a few questions hopefully someone would be so kind to answer.

Question 1:
After I was adding the oil charge, the readings for the low/high side was 30/200 psi and the ambient temperature was 72f. Going by the charts on this page http://ift.tt/1TfgOfm
My low is slightly too low and my high is slightly too high meaning there is some blockage in the system. Are these numbers far enough beyond normal that I need to start disassembling the A/C system to hunt for blockage?

Question 2:
After I added the dye, I checked all of the lines visible from above the engine compartment and found no leaks. I know that a common failure point is the evaporator that is buried in the dash and that it's a monster bitch to get to. I still need to check from beneath the car and underneath the airbox. Any other suggestions for places to look?

Question 3:
Does anyone have any more general advice or actions involving my current situation.

Thanks in advance guys. This board has been very helpful so far.

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Need advice on A/C repair.