the dreaded ac questions

have a no cool issue on my 08 ls5 . when I bought it about 2 years ago it seemed no to cool so well .added a 12 oz. can of 134a and all was well until about a month ago . thought the same was before and added another can . well not using good sense and without researching I added another can . woa . the high side pressure went crazy . well after I found out the correct quantity ( about 16 oz. ) I descided just ruining the ozone layer a little more , I bleed of until the low side came down to about 25 psi and the high side to about 250 psi . seems ok as for pressure but no cooling at all . the radiator fan is running . the compressor is working with stated pressures I would think . and with these pressures I would think the expansion valve is working . any ideas ?? the car has about 125k miles on it . runs very well .

thanks ,

Armond Martin