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Old 12-17-2019, 11:01 AM   #365
joedoh
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Join Date: May 2007
Location: Doodah Kansas
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Re: 57 Panel "FAKMLC" build

sorry, i missed that. reading back, fan 1 is for low speed? and fan 2 is for high speed? you can only use that on fans that have a separate low speed and high speed wire (three wires total). if your fan has two wires (power and ground), you can use either fan 1 or fan 2 output from pcm and the fan will run full speed. if you have a fan with 3 wires and two speeds, you will need two relays, which it sounds like you have in the harness? the 12v supply should be in parallel

older BMWs had big giant fan resistors on a 2 wire fan, so that a fan 1 signal went through the resistor, and fan 2 signal bypassed it, making a 2 wire fan a 2 speed fan, but the resistors predictably went bad all the time from the super high current being resisted, 12v at 30 watts us 3600 watts, cutting down the speed took about a 1/4 of that, so the resistor was in the area of 900watts! the resistors on the shelf at radio shack are 1/4 and 1/2 watt, so a fan resistor was huge and packed in sand to dissipate the heat of resistance (thats where the energy goes, 900w turned into heat and 2700 watts goes on to the fan)
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