Hi. The air/con compressor will not run unless the fan is running. It used to be that on the low setting the fan power is lowered by a simple coil of resistance wire in series with the motor circuit on that setting. A very crude but effective set-up is through that coil. For 'ventilation', it is on a small 'plate' mounted behind, inside, the drivers compartment fire-wall. Pretty hard to find and get to to remove it. The coil burns out and has to be replaced. Pretty much like the old-fashioned electric radiator element.. One Toyota gent said to find it you have to trace that particular wire from the fan speed switch. Crude, yes all the way..Good luck.