The cooling system is operated by the rheostat switch (79) This has 4 positions : position : completely non-operational. - 2nd. position : - console fan feed (77) speed, - feed for fans (70) and (71) using relay (72) - feed for cut-in (75) control circuit - 3rd. and 4th. position : 2nd or 3rd. speed of console air fan (77) which makes it possible to adjust the cool air output.