Hello, did you try putting the switch in the medium position and then
turning on the head lights ,or the heater moter.Should konk out also.  I
have always heard that the engine runs off the alternator,but starts with
the battery.Maybe you have a bad alternator,or voltage regulater inside the
altenator .One that is not putting out enough current to run all that
stuff.Try reving the moter a bit and then turning the switch to the high
a/c position.My bet ( uneducated in these matters ) is the voltage
regulater.