If you only get cold air when the car is moving, I still think that the radiator is not getting enough air forced through it. Revving up the engine will make the compressor turn faster and circulate more r134a through the system. The pocket data booklet says to rev the engine at 1500rpm for getting the coolest air, for what that means.
If it is really 104F (40C) in CA, then the best you can expect is about 70F degrees at the vents. Those northern climate guys at Volvo just don't know how to keep a car cool. But they are nice and toasty in the cold climates.

Klaus
The cabin temp sensors are behind the grab handles. Use a small screw driver and pry the plastic cover off the ends from the top side. You will see a small grove at the top where the handle starts to go away from the side of the car. The plastic is attached at the bottom, like a hinge. Two 10mm bolts hold the handle in place. After the bolts are out, lift up on the handle and then pull straight out.
The square cover over the temp sensor just pulls straight out. Use a wet Q-tip to clean the very tiny sensor. Be careful not to bend anything.

Klaus
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98 V70Rawd(108Kmi), 95 854T(88K mi), 75 164E(173K mi)