The compressor has three rpm speeds one can select by connecting one of three wires (orange, green, and white, need to check colors:wacko:) to the evaporator signal wire. Or a three way switch is available to select speeds "on the run". I did not want one more controller, so tried the slowest wire connection and then settled on the second one after considering amp draw by the compressor and generation from the alternator. Not optimum or sophisticated but adequate for my purposes.