Heater switch resistor

[Guest chrysleritis]

Hey everyone,

I discovered the reason that my heater fan motor will not switch on to low speed -- the little wire resistor on the switch terminals had given up and burned out. I can only do "off" and "high" for the fan.

It doesn't show, so I'm going to use a modern wire-wound resistor. Can anyone tell me what the resistance and power dissipation is on this resistor?

Thx.

[Norm's Coupe]

I don't have one of those handy to look at. However, normally resistors have stripes on them in colors and sizes. Those stripes usually indicates the resistance of the resistors. So, all you have to do is match it up at the store. Or, so I've been told anyway.

[Guest chrysleritis]

Nah, it's a little wire-wound resistor (low-resistance, high power) encased in a ceramic spacer. It looks about the same as the resistor on the switch for the famous dimmer switch for the instrument lights. That switch gives you three possible settings for the instrument lights: dim, off, and offer. Same basic resistor deal.

[Plymouthy Adams]

The resistor I just measured on the fan switch here is 2.2 OHMS..and the wattage would be at minimum 5 watts. The wattage size will be the ability of the resistor to dissipate heat..the by-product of resistance. You could use a typical dropping resistor as used on a 12 volt ignition. To cut the motor speed in half you need the equivilant of the motor resistance inline with the battery..you can measure the motor windings and get a more accurate resistor...but in reality I think I would just grab a coil dropping resistor and try it out..it will be more than enough wattage for the fan motor...

[DutchEdwin]

Your fan motor would take as much as about 8 amps on a 6V system.

This would be P=UxI= 6x8=48W.

I do not know it the resistor is in series or parallel to the motor windings.

If it is parallel, using a 2.2 ohm resistor

U=IxR -> I=U/R 6/2.2= 2.73Amps.

In heat this means, P=UxI 6x2.73=16Watt. That's a lot of heat.

Someone should be able to tell if it is in series or parallel. That way, you can calculate the power it should withstand. Any shop that sells electronical meaterial will sell these high power resistors.

I've Had the same problem, only my resistor just changed in resistance, evaporated material over time. The resistor I used is a 10Watt resistor.

Be careful not to let it touch any wires, it will sure burn them.

Edwin

[Jim Saraceno]

You can buy those switches that bolt onto the bottom of your dash.