Question 3 speed fan speed pulled off .help

Mar 22, 2020
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The fans in the case I'm building a new pc has fans with tiny switches marked LMH. One of these switches got pulled of the short length of wire that comes out the fan (besides the power plug) There are three wires : Black, Yellow, Red. I can't get the switch back on but does anyone know what wire goes to what for each speed......and if it's just simple changeover switch, which is common ? help appreciated..
 

k1114

Titan
Moderator
If it's wired the same as molex: black is common, red 5v, yellow 12v. Black+red=low 5v. Yellow+red=med 7v. Black+yellow=high 12v. If it's pwm red and yellow will be switched and you should notice the difference in speed from low vs high.
 
Mar 22, 2020
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Thanks for the suggestion Titan...There are only two wires on the power input (Molex, R+Bl.) which presumably is 5v. Then there's the R,Bl,Yel wires to the tiny switch. Unless there are electronics in the fan there can't be any 12v available. If there is electronics in it, pwm may be what's happening.
I have managed to open the switch "case" and there's a mini slider switch inside .I will test today to see if it is a c/o switch or something else..I'll be back..
 
Mar 22, 2020
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It's not a simple c'o switch..if I call the three terminals a,b,c, as slid thru L,M,H
at low speed: all open cct
at M speed: a > b
at H speed : a > c.
As I still have no clue as to which of the 3 wires pulled off which terminal, in this case it doesn't matter because low speed will be quite OK. So I can leave the switch disconnected. It is presumably SWM control.
 

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