Fan switch glowing red??

[agnes the dog]

Hi, hope you aren't getting tired of these questions, but this one is concerning. I leaned into my truck today at just the right angle to see that the switch that controls the heater fan speed was glowing red at the back (inside the dash). It only did this on the middle speeds - not high or off. It looked like an old electric heater element. To me, it looked very hot. I didn't leave it on long enough to find out. I assume that this is not right. Anyone ever see this before?
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[mr48chev]

That is because basically that particular one has a resistor in it that acts as a heater element. The resistance controls the voltage getting to the fan motor controlling the speed but causes the element in it to get hot in the process. I burned the daylights out of my hand on one of those when I was a teenager and grabbed the one in the car I had at the time.

[1project2many]

There's usually a small ceramic tube covering the resistor but it might have broken or maybe that particular switch doesn't have one.

[agnes the dog]

I pulled some things out of the way and saw that there is a ceramic tube, but it's only on the ends. It looks like its supposed to be that way. There is some blackening above the area, so I guess I'll just use it on high or turn it off until I get a new resistor. Thanks for the info. It was helpful!
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[Highsider]

I always learn new information on here!

[mr48chev]

Does it control the speed of the fan when you turn the knob or only work on high? If it controls the speed it is working right and when it works right it gets hot.

[63 & 64 Bowties]

They do usually get hot, but I can't remember ever seeing one glow red.
When the switch is in the "high" position, that resistor is bypassed, the contacts are direct at the point. That's why it doesn't do it in high. Do the wires running to and from the switch get hot in High? Any possibility you have remnants of a mouse nest in your fan?

[agnes the dog]

Originally Posted by mr48chev

Does it control the speed of the fan when you turn the knob or only work on high? If it controls the speed it is working right and when it works right it gets hot.

It works correctly on all positions.
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[1project2many]

As a fan fails, or as the bearings dry out, the current used by the motor tends to increase. This might be the cause of the resistors glowing. And if the current draw through the fan is too high you are likely to burn up the switch even by running it on high thanks to resistance at the contact point inside the switch. You might want to pull the blower motor and check / lube the bushings.

[agnes the dog]

Originally Posted by 1project2many

As a fan fails, or as the bearings dry out, the current used by the motor tends to increase. This might be the cause of the resistors glowing. And if the current draw through the fan is too high you are likely to burn up the switch even by running it on high thanks to resistance at the contact point inside the switch. You might want to pull the blower motor and check / lube the bushings.

Thanks. That's a good suggestion. Any recommendations on where and what to use to lube?
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