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Old 05-12-2021, 10:11 AM   #18 (permalink)
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Originally Posted by EcoCivic View Post
I was finally able to get a measurement. At idle with the alternator off, I see a draw of about 16 amps for both fans. At 70 MPH I see a draw of about 9 amps from the fans and there is definitely a spike in current draw when they start up, but there appears to be less of a spike than when idling. This seems to indicate that the fans do spin while driving down the highway, but at less than full speed. Not sure how the alternator being on affects this yet, but there are definitely power savings to be had from shutting the fans off on the highway. Although the reduction in alternator drag would be impossible to see on my MPG by itself, it will significantly save my battery when driving around with the alternator off and possibly extend the life of my alternator as well since it won't be working as hard.
The fans will run at whatever their predetermined speed is, typically there are two speed settings. The current draw is due to the different amount of work the fans are doing.

As the fans are being assisted by the flow of air forced through the radiator, it reduces the power requirement for any given fan speed.

I didn't read the entire thread, just cruising through so I apologize if I missed it. One possible fix for keeping the A/C from running the fans would be to have a secondary relay that interrupts the circuit below a set speed. Or even a separate fan controller at a different temperature monitoring the hot side of the refrigerant.

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EcoCivic (05-12-2021)