Can anyone help as to how the type of fan in the picture works?

I believe when the aircon is on the fan runs at reduced speed, and goes full speed if the temperature dictates.

I'm wondering if its possible to use the fan in another car, and use a switch, to switch it on at reduced speed for town driving, effectively replacing the aircon trigger with a switch, does anyone know how the three wires are connected?

I'm guessing the two thick wires run the motor via the aircon / relay, and the third wire when grounded runs it at full speed, I don't want to go connecting things up and blow something in the control box.


mondyfan

The thin wire is a pwm control signal from the engine ecu, some have a variable 0%=off 100%=full speed operation, some use set levels of pwm for preset operation states.
I can't remember offhand which scheme ford ones use, autodata might help here, but it is likely a 5v based signal.

The 2 thick wires are earth and permanent live, there was a recall on focus's due to these units getting damp internally and operating by themselves - they didn't fix the fault but added a relay that cut off the permanent live when the bcm goes to sleep mode.

Dave

Cheers, I'll build a pwm module and give it a try...

I've had a look at autodata, is it a 2007 model year vehicle that the fan came from? Autodata shows a twin speed fan with 2 relays upto 2006, and the pwm controlled one from 2007 onward.
I've only got pinout data for the 2007 onward diesel models, it shows a 12v pulled down signal, so should be that the module supplies 12v at the thin wire, and the control unit pwm pulls it down to <1v.
I've just changed a control unit on a later volvo (appears to be delphi not bosch though), and scoped the signal which seems to be very similar to the one given for the mondeo as above, approx 10% duty at fan off, and 90% at full speed.

When changing speed it steps through the duty cycle, no sudden jumps in the duty cycle.

Waveforms here
https://www.dropbox.com/sh/wwu3pjo4ao8ntzq/AAAD9n2_DMnr45n3gkIhTG-sa?dl=0


Dave

Eta
These are instructions for an aftermarket fan controller, might be useful as some control module specs are given.

https://cimg1.ibsrv.net/gimg/ls1tech.com-vbulletin/537x750/ebay_pwm_fan_controller_instructions_1_0d507c1ede0dcf9009e23678fb721caf99d50904.png


[Edited on 19/4/21 by obfripper]

Thanks, some useful info there.

I'm not sure of the previse year, but sold as 2003-2007, TDCI, I know the thin low current wire is to the ECU, so will have a play with pwm.