I agree with Jeff, use the electric motor to run the ac and other stuff you find useful like power steering depending on vehicle weight. I saw ditch the adrino crap and just rig it up to work on 2 12 volt deep cycle batteries. This way you can run it on 12 volts for low speed and 24 volts for high speed by wiring up a dtdp switch for one way or the other.
K.I.S.S.