Turn off the switch at the main circuit breaker for the Rheem air conditioner. Tape the switch in place so that it isn't turned on by accident.
Turn off the power at the breaker box located near the compressor. The compressor is the part of the air conditioner that sits outside your house.
Use a screwdriver to remove the electrical panel on the side of the Rheem compressor.
Use a pair of wire strippers to remove the last half inch of covering from the wires leading to the breaker box.
Look for the terminal connection cluster in the center of the panel opening. Depending on your Rheem model, this could be a series of plastic tabs with cylindrical openings on the ends or a plastic block with screw terminals.
Connect the wires from the extension box to the terminal as follows: connect the black wire to the terminal opposite the red wire, the white wire to the terminal opposite the blue wire and the green wire to the terminal opposite the other green wire. Once the wires are wrapped around or inserted into the terminals, tighten the terminal screw with a screwdriver.
Replace the electrical panel cover. Restore the electrical supply to the condenser unit.