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Old 02-12-2021, 10:29 AM   #1
2JZFC
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Default Questions On 740 Fan w/2-spd Relay

Greetings.

What is the maximum amperage draw for this unit, accounting for kick-on and hi-speed?

If the 2-spd relay unit's power source is fused SW12V coming from a distribution block, is another relay necessary?

TIA
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Old 02-12-2021, 04:24 PM   #2
bobxyz
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I'm not familiar with 740s or 940s, but on a 240, the extra fan just for added A/C cooling is fused off the battery at 20amps. I'd guess a dual fan for primary cooling would need 50amps, or more.

You definitely do NOT want to connect the main fan power to switched +12v, or you'll burn up the ignition switch. Flipping though some 940 wiring diagrams, those fans are powered directly from the battery junction block, or maybe through a fusible link, but no fuses. The relay coil circuits are low power and come from switched +12v.
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Old 02-12-2021, 08:03 PM   #3
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700/900/850/x70I 2-speed fan relay is ground controlled and has constant 12V. Full speed takes around 30A when it's switched on directly. Depending on stuff it's a bit under or over. So if low speed is always switched on first then 30A is enough.
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Old 02-13-2021, 12:31 AM   #4
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Thanks, guys.
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