One year later on repair job work well with car now at 225000km. However the AC compressor vibration - whining noise returned last fall as the weather got colder. I did not use A/C during winter here in Canada and when I turned on in spring the whining noise had returned. I connected A/C gauges and everything looked OK but LP side was around 30 psi on a 40F (5C) day with car running. Thinking that the desiccant bag was blocking again I decided to lower the pressure while car was running. Interesting find in that as the pressure got lower (LP25psi, HP100psi, 40F) the noise got louder. So I decide to add gas to the system. Once the LP pressure got to 40psi the whining went away. I charged it to LP-45psi, HP-160psi and 40F. No noise now and blowing cold air.

I am not sure why this whining occurs at both high and low pressures. At a high LP pressure I assumed that there was too much gas and I was getting liquid carry over from the evaporator. This is also the reason that Volvo has a software change to lower the evaporator level. At low LP pressure I assumed that the compressor is going to full stroke to maintain HP pressure constant. Either this full stroke or too low gas level now causes whining to occur. Finally the new style variable displacement compressor used on the newer 2007+ P3 series cars tries to maintain the gas pressure constant for various engine speed over a range of temperatures. This probably requires a tight tolerance on gas charge (.8 kg R-134 XC70) which implies a certain operating pressure.

In summary there seems to be a "sweat spot" for LP pressure that will prevent whining on the 2008+ variable displacement AC compressor on P3 series cars as stated below:

LP-30psi - Too Low. Whining appears
LP-45psi - Good.
LP-70psi - Too High. Whining appears