What does a Evap. Temp Sensor do? Can it cause a clutch on the compressor to cycle on and off at will ?

Also, is there anyway I can test to see if my expansion valve is functioning correctly. Every AC guy I have personally spoke to has said my problem sounds like a clog. But I have been able to take my air hose and spray through every hose on the system as well as the condensor and evaporator and air blew pretty nice throughout all of them. So I dont believe I have any clogs there ( not to mention the hoses/compressor/dryer/sensors/plugs are all brand new within the past month as I have been trying to fix this damn AC.

Cory