Fan blower resistor??? I've got a question for those who know about it.

[Bbasso]

On my 2001 E350 my low speed, medium speed, high medium speed doesn't take much voltage but when I turn it up to high(max) speed it draws well over 1 volt according to my gauge.
Does anybody know if the blower motor resistor goes bad over time?
The reason why I'm asking is I haven't noticed that much of a draw when it goes to high until recently...

Any methods of checking it?

 

[Mwilliamshs]

It does not draw a volt. It runs on 12-14 volts. What guage are you referring to? If the fan runs on all the speeds and the speed changes depending on switch position, the resistor is doing its job.

 

[Buddha.]

Do any of the other electrical loads lower the voltage more than they used to?

 

[Bbasso]

The guage I'm referring to is the digital one I added a long time ago.
The other settings on the fan doesn't make the guage move until I max out it then it takes the reading from 14.2v down to 13.0 and sometimes much lower.
Yes, I'm aware every vehicle runs on 12v in 99.9999% cases And I'm also aware that the fan uses and all accessories use the provided 12v .
And each accessory draws a specific amount too.

Nothing else is effecting the readout like this.

 

[rontaki]

There's no place like Ohm

Measure the voltage across the resistor, and use ohm's law to calculate the current through the resistor. The fan would need to be on and in a setting that uses the resistor, likely a lower speed setting.
It would be good to measure the value of the resistor as well. Be sure the power to the fan is off while taking the resistance measurement.
The resistance should be within 20% of the marked value. Compare to the manufacturer's specification.

There is an ohm's law calculator at http://www.ohmslawcalculator.com/ohms-law-calculator.

Below is cheat sheet of formulas to assist as needed.

 

[Bbasso]

Thank you.
I'll give that a try this week.

 

[rontaki]

Thank you.
I'll give that a try this week.

You are welcome!
I should add that I meant the power to the fan circuit should be off for the resistance measurement, whereas the fan needs to be on and in a setting that uses the resistor, likely the lower speed settings.

I'm going to add that info to my original post also, wanted to be sure you see this addendum.

May the (electron) force be with you!

 

[Mwilliamshs]

Since I'm left to assume, is "the digital one [you] added a long time ago" a voltmeter wired directly to your OE start battery? The voltage drop you see isn't due to the voltage used by the fan, but rather the amperage it's pulling. The blower motor resistor is actually multiple resistors. Some are even put in series for certa in speed settings. The slower the fan turns, the more resistance has been added to the circuit. The fastest setting has no added resistance; the fan is given full voltage in that position. The blower motor pulling enough amps to drop system voltage is either perfectly normal or your voltage regulator isn't keeping up, or the alternator isn't working as it used to, or the switch isn't working as designed...could be lots of things or could be nothing. Can't help someone who can't answer questions to help themselves

 

[V30CREWCAB]

Hi speed on a blower fan is straight thru, no resistor. the resistor is there to lower the voltage for the lower speeds.

 

[Corneilius]

Hi speed on a blower fan is straight thru, no resistor. the resistor is there to lower the voltage for the lower speeds.

Well then from that maybe it is operating appropriately, have you got another ford van handy you could use as a baseline Rob?

 

[Bbasso]

Not atm...
I decided to go to the range instead of working on my van today...