Hi could anyone point the location of the a/c expansion valve in the cayenne and how to get to it i see by the parts diagram that is close to the evaporator. is the valve on the driver or passenger side and how difficult is the valve to change. thank you.

 

It is access from the engine compartment. You raise the cowling on the passenger side, and it is down and toward the center of the vehicle, near the DME. It is not too bad to change given the proper tools, make sure to have your refrigerant captured, and to re-use it, if it has not all leaked out. Might not be a bad idea to inject some a/c dye into the system as well.