I thought about using the original MR2 fan control box. But to me it's a black box. Don't know how to wire it into my new harness. I could buy a fan controller and plug it in, but where is the joy in that?! I like making it up as I go along.
So I have devised an ingenious (in my own simple mind) plan to activate the fans using 2 relays, the stock thermistor and a variable potentiometer.
Control for radiator fan therm
As you can see from my schematic, there is a small relay inline with the stock thermistor located in the radiator, and a potentionmeter. When the resistance across the thermistor drops to a certain level, enough voltage will flow across the relay to trip the high side. This in turn will energize the larger relay and start the fans.
Why two relays? We know that the resistance through the thermistor drops as the temperature rises. At some point the amount of electricity passing through the thermistor will be large enough to energize the relay. By using a small, sensitive relay in series with a potentiometer, I can precisely determine the temperature at which the little relay will be tripped by increasing the resistance. I do not believe that the thermistor would be able to trip the single large relay at a high enough resistance.
Any suggestions as to why this idea should not work?
and should work providing the internal resistance of the potentiometer isn't exceeding the resistance of the large relay which u
are controlling