An air conditioning system for use in an over-the-road or off road vehicle
provides operation during both engine on and engine off conditions. The
system includes a variable speed compressor, a motor, and a controller.
The controller receives electric power from the vehicle's electric power
generation system when the engine is on to enable operation of the
compressor during an engine on condition. When the engine is off, the
controller receives electric power from a battery to enable operation of
the compressor during the engine off condition.