Purchased a LG LW2510ER window air conditioner for emergency conditions (ie.. main AC just died) the only 120/240 plug I know of in the house is the dryer plug. Trying to build an extension cord to run the dry power to this plug but not sure how to connect the 3 wires to each other. Air conditioner side of the extension cord is a female standard 250 3 wire with the 1 perpendicular contact (rated 20a). The other side is the male nema type 10-30R connection

Guys, I got it... after determining what the standard 250v 3 wire nema name, I found the correct diagrams. Can't be too safe... Thanks