The trianry switch is mounted on the reciever/drier. This controls the low pressure cutout and high pressure (cooling fan). Take a shop light and place at the back of the radiator and look through the grille and see if any there is any visiable light. The compressor is a variable stroke type which is increased on demand. The expansion valve, controls the amount refrigerant entering (liquid) into the evaporator. Any of these components can cause the problems you are having. Is the high pressure line going to the evaporator cold and frosty? Then I would think the expansion valve is bad. If not I would be looking a the switch, compressor, or a blocked condensor getting no air. Steven.