Ok I feel like a moron here, But how do you connect the 240 to the pressure switch? There are only connections for 2 wires plus a ground. As far as I know to have 240 you need 3 wires. What am I missing? No compressor manuals I have found online make any mention of how to wire them in, nor are any of the similar questions of this nature on message boards ever answered with a "red wire goes here, black wire here, and white wire here." Am I totally missing the point and the neutral just hooks to the ground (white to green)? Why is this such a closely guarded secret?
For a 240 volt compressor you hook the red and black to the pressure switch .
You hook the green to ground and tape the white of.The Neutral is not used. Never connect the neutral to the ground anywhere except at the designated system ground point. For most services that point is in the main distribution panel.
As Terry said, 240 only needs 2 operating wires, you can use a 2 conductor plus ground cable also, re-mark the white with black tape as a "hot" lead. As he said, disregard the white if you have a 3 conductor cable. In a main service entrance panel N and G are essentially one in the same for grounding purposes, the grounds may be conected to the N bar in these panels. A subfed will have a seperate ground bar, connect ground there. Essentially you want a ground wire connected to the frame of the unit all the way back to the N in the main panel, it may be bare or green.