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Agreed Occasionally6, ...in fact these PWM's come with potentiometers and control knobs, so that's probably the easiest way to use them: just mount the supplied control knob and pot' on the dash, extending the wires if necessary. I would want to be careful not to run so low a voltage to the motor that it won't turn though - in case that damages the motor. I'd probably want a 'bypass' resistor for the lowest speed.
Actually I prefer, when driving, to have a tactile indication of what level I've set things to. I kind of know, under given driving conditions and at a given vehicle speed, that blower speed 1 will be enough, or that I'll need blower speed 3 for a while and then can drop down to blower speed 2 once the windscreen is clear for example. I also quite like the idea of not having an extra control knob on the dash if it's not needed. Ideally, I'd have four trimmer potentiometers back in the guts of the wiring connected to the PWM and switch between them using the stock VW control switch on the dash. That way I could infinitely adjust each blower speed to my own requirements and then when I have them right, leave them alone and use the stock control switch.
But I'm not clear about how these things work. (E.g. why do potentiometers need three wires?) I know some of these PWM's can have a 'control voltage' input between two contacts (0v - 5v for some PWM's) to control the output power voltage, but I don't know if the one I bought can accept that. (I guess I should ask the guy in China I bought it from.) That would make life really easy as I could then simply solder resistors between the output terminals of the stock VW speed selector switch.
But that's for another time. I've been puzzling over the installation instructions of this Kenlowe coolant pre-heater, trying to decide where it will fit best in my engine bay. The unit looks well designed and well made.
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