What exactly is the extension valve for the A/C unit for?

I was told I needed this part so that my A/C would work properly again..

Anyone got pics?

(Would post this in the 4sale section, but not sure exactly what I'm trying to buy..)

 

Are you sure you don't mean expansion valve?

 

I'm not sure, I've been trying extensively to search wtheck a Extension Valve was to no avail.

Expansion or Extension can easily be changed in the mix with an Asian Mechanic with an accent..

Going to search it out.. thanks