Where is the A/C Expansion Valve located?

My van has front and rear A/C, but we capped off the rear A/C lines from the condenser because of a leak in the rear lines. In troubleshooting my inoperable A/C, we replaced the evaporator, condenser, compressor and the kit that included the orifice tube. But we could not figure out where the expansion valve goes. Can you provide a diagram of where this is?