Allot of times the expansion valve comes with the low pressure line. I wouldn't really worry bout the valve but since you are changing the compressor, the guy should of told you to change the receiver dryer which is usually with the condenser.
I don't know if this stuff is the same on a 2008...should be.
But the expansion valve should be on the engine side of the firewall where the low pressure line connects to it. The other side of the firewall is the evaporator.