radiator cooling fan resistor values?

[JayG]

Originally Posted by DennisAN

Be careful to "zero" your meter when dealing with such tiny ohm values. It is possible the measured values in the above post are in error by 0.2 ohms each, when the real values would be 0.0 ohms (i.e. a wire) and 0.6 ohms.

What YEAR is the OP's car? The resistor value appears to vary between model years.

The FSM for 2000+ cars shows only a single resistor per fan motor. Both are shown as 0.55 ohms on the schematic diagram.

To calculate the wattage you have to account for the resistance of both the resistor and the fan motor as they are operating in series to ground. Once you have the overall amperage, you can then backtrack and apply ohm's law to the resistor itself to determine its minimum wattage rating.

That makes sense, that the measured values are off by ~.2 ohm. I believe that on HIGH, the fan get the full 12v and on low it is lowered by the resistor in series

Now the fuse for each fan is 40 amp, if it was a full draw of 40 amps, it would be ~440 watts

12 volts through a .55 ohm resistor is ~260 watts or ~21 amps.

My guess is that the low speed resistor is ~ 300 watts rating if .55 ohm and ~250 watts if .8 ohm

What gets interesting is that the voltage drop on a .55 ohm resistor with a 12 v source is ~11.5 volts. That leaves ~.5 volt to the fan

If we go with .8 ohm as measured, then the current is 15 amps and the voltage drop would be 8.25 volts leaving 3.75 for the fan. This sounds more realistic than .5 volts to the fan

if the actual voltage is higher, say 13 volts than the voltage to the fan will increase slightly and the fan speed would be higher

Maybe a measurement of the voltage after the resistor would shed some light on this

Of course if my calculations are wrong, then fo-ged-about-it