The Stovebolt Site Forums The Shop Area The Electrical Bay A glowing situation....

Just finished hooking up the heater blower motor on the 52 and while test running it noticed the resistor on the back of the blower switch was glowing red HOT on the two lower speeds!!!!I know a resistor will get very hot but holy cow that hot???? still 6 volt and the heater switch is not the one with the round knob on it, it works like a toggle switch, found it in the glove box still in the GM box.

Mr Goodwrench,

Break out the hot dogs and beer! It sounds like it's doing what it suppose to do, slowing down the blower motor and getting hot in the process. The only missing info is..is the switch rated for that duty? I would guess that a rheostat like that would be rated for WATTS. This would be dependent on the supplied voltage and draw of the motor. Maybe the treasure you found in the glove box isn't husky enough to shunt the current without turning into a barbecue, it's too small. Could this be possible!

Stuart

When I was a kid my father left me alone in the tow truck while he went into a parts store. I was goofing around under the dash and blistered my fingers on the heater switch. That's when I learned how hot 6V gets. It's a lower voltage, but higher current. The resistor is removing(and releasing) the current that you remove for a lower speed on the fan.

Dunno stu??? It's a originall GM heater blower switch that was still in the GM box, old box at that looks like maybe from the 40's or 50's???? may not be correct for a 1952 truck??? It's dark brown with a light tan lever sticking out the front of it that says heater. I could get the part number off the box tonight if that would help. other than glowing red it works fine off, high, med , low

Sounds like a paddle switch and that it's operating normally.

Mr Goodwrench,

It sounds like it's the proper switch then. I have read on this site they do get hot enough to burn a finger but didn't realize they would get hot enough to glow bright red. I guess the only other thought would be binding or wear in the fan motor which would cause it to pull more current.

Stuart

On the lowest speed, it's not uncommon for the resistor coil to get red hot. Later model speed reducing resistors were incorporated into the airflow of the heater housing to keep them cool, plus put them out of reach to prevent burned fingers on nosy people!
Jerry

Hey - I resemble that remark!

that's why mine is in the engine compartment away from most everything.

I would disagree that the dropping resistor should/would/does glow red hot under normal circumstances. For one thing the resistance element or coil is potted in a high temperature ceramic coating and would emit any color. If it was glowing then the ceramic potting compound is probably blistered off of the coil. So if it is literally “glowing red hot” then the coating is probably missing which is exposing the bare resistance wire to the atmosphere and allowing it to become oxidized and eventually burn out.
So I would say that for some reason the circuit is pulling more current than it was designed for and that the over heating has already damaged the wire wound resistor coil on the back of the switch.
Denny Graham
Sandwich, IL

Thanks guys, I have it mounted away from everything and will keep an eye on it. I think I will measure the resistance on both resitors before I toast it though.