Radiator fan - why four wires instead of two ?

[Grossel]

Hi.

Same car as discussed here:

Wire designation on complex coloring schemes (Nissan 2000)

Hi. I'm helping a friend that have a Nissan x-trail from 2001 with an electrical issue. We suspect there may be some fault to the actual wiring itself (car have be subjected to rough treatment some years back). In order to help myself to locate the fault, I make a schematic (my own, that only...

www.electro-tech-online.com

So, we took out the radiator fan because we initially taught it was dead. However, I managed to get it to run by using a small simple 12V transformer+rectifier (doesn't immediately broke if shorted, and too little maximum current to kill the fan motor).

But the question is why car manufacturer seems to put four wires to a fan? The measured resistance between each wire is too low to determine anything, therefore I tested on bench.
The test results yields the following observed result (omitting all test resulting in running in opposite direction).

See table below (I'm somehow not able to put cursor after table, so the table have to come last)

I also measured the voltage between the poles not used when fan was fed by two wires, i.e. while fan running for second last line in table, I measured just above 2.5VDC between black and blue (the weak transformer only manage to output ~6V to the fan running).

Because I doesn't have tested with a proper PSU yet, I'm not sure if the fan is fed using all four wires (like in last row) using a proper 12V supply will simply cause the fan to run faster (because the weak transformer itself is the main limiting factor). But then again why waste an extra wire if it turn out 3 wires should be enough ?

black wire	Yellow wire	Green wire	Blu wire	Result (does it run)
negative	nc	nc	plus	runs ok
negative	nc	plus	nc	runs ok
negative	plus	nc	nc	No running. Near short (around 2 ohms)
nc	negative	nc	plus	runs ok
nc	negative	plus	nc	runs ok
negative	negative	plus	plus	runs ok

 

[atferrari]

Risking yo say something ridiculous, one of those inputs, could it be an input for PWM signal as in PCs fans?

 

[Diver300]

A lot of car fans run a various speeds. One way of doing that is to have several brushes and they are connected ind different ways to give different speeds.

Unless you have a really powerful supply and some way of measuring the speeds, you may not be able to tell which connections are giving faster and slower speeds.

This thread (https://www.electro-tech-online.com...-wiper-motor-circuit-this-complicated.164779/) was about two speed wiper motors, which are often achieved by having three brushes.