my 2 cents

- Check the low side and high side pressures
- Find leaks, put UV DYE (inspect exterior and perform internal scope to check evaporator core)


EDIT:
Added a link: Troubleshoot Automotive Air Conditioning Problems

__________________
Build Date: 06/2004

2004 E53 3.0L 6 Cyl
Engine Code: M54
AT: 5L40-E/GM5 (A5S 390R)
http://s101.photobucket.com/user/lho...in/library/E53

2004 E46 M3 Coupe 3.2L 6 Cyl
Engine Code: S54
MT: S6S 420G - 6 speed
http://s101.photobucket.com/user/lho...in/library/E46
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Build Date: 10/2008
2009 E90N 328xi Sedan 6 Cyl
Engine code: N51
AT: GA6L45R/GM6
http://s101.photobucket.com/user/lho...in/library/E90