I just had my Sienna's A/C checked because it is taking a long time to cool and doesn't cool all that great.
Mechanic told me Sienna's with dual A/C (front and back) operate like this.
Try this. 2009 is actually still gen2 but it’s still pretty easy to do (bumper cover must be removed). I had the same symptoms as you in our 2007 and cleaning the condenser made a significant improvement.