A/C fan knob very hot - Page 2 - LotusTalk - The Lotus Cars Community
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post #21 of 26 (permalink) Old 08-13-2019, 06:00 PM
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I have this same problem. 2014 Evora. Has anyone solved it other than limiting fan speed?
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post #22 of 26 (permalink) Old 08-17-2019, 03:29 AM
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I have the same problem... anyone solve it?
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post #23 of 26 (permalink) Old 09-02-2019, 06:52 PM
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I just noticed the hot knob on my 14 this past summer, on a long day of driving, definitely left me feeling uneasy.
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post #24 of 26 (permalink) Old 09-02-2019, 08:07 PM
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Just a thought, but why not start a new thread instead of bumping one that is X amount of years old? It seems to be a habit here, and I'm not sure why.

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post #25 of 26 (permalink) Old 09-03-2019, 08:39 AM
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Mine gets warm too. I once met an embedded engineer in MD who intended to create a more modern HVAC control system on his Evora and sell it, but I never saw anything pop up on the forum. The knob gets hot because it's conducting up to 20 amps of current (fuse C35) through a mechanical switch, and it regulates the fan speed by dumping energy into a voltage divider (notes section SN, p. 52). The resistors heat up as they convert that electrical energy into heat. The contacts inside the switch can also be dirty, adding resistance where it isn't ideal, emitting more energy as heat (and presumably this is the potentially dangerous part, as the resistor package was designed to take it).

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post #26 of 26 (permalink) Old 09-03-2019, 02:23 PM
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Originally Posted by MGB View Post
Mine gets warm too. I once met an embedded engineer in MD who intended to create a more modern HVAC control system on his Evora and sell it, but I never saw anything pop up on the forum. The knob gets hot because it's conducting up to 20 amps of current (fuse C35) through a mechanical switch, and it regulates the fan speed by dumping energy into a voltage divider (notes section SN, p. 52). The resistors heat up as they convert that electrical energy into heat. The contacts inside the switch can also be dirty, adding resistance where it isn't ideal, emitting more energy as heat (and presumably this is the potentially dangerous part, as the resistor package was designed to take it).
Pretty sound reasoning. But could be why the S1 knobs were all metal; they can sink the generated heat without fear of melting. I can't recall if the 400 knobs are metal or plastic.

2011 Evora NA - Phantom Black | Paprika | MT | 2+.5
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