Budget underhood AC retrofit.

My 1969 Dart had factory air and a similar-looking expansion valve. The thin copper tube is a "gas temperature sensor". It slid into an internal "temperature well" tube that was inside one of the refrigerant tubes, which I am guessing would have been downstream of the valve. The purpose is to proportion the flow to maintain a constant temperature in the evaporator. If it goes above the boiling point, the valve opens to let in more refrigerant. That works better than the fixed orifice which GM cars used thru the 1970's. Modern expansion valves are the same, but the temp sensor is integral with the valve. The problem with using them is that all in my cars attach to flat blocks, w/ an O-ring face seal, so might be hard to adapt. Those using an under-dash knee-knocker climate unit need not fool w/ an expansion valve since they are built into those.