I've got a radiator cooling fan from an '01-'03 Volvo. I want to use it in an old Buick. The volvo fan has a speed controller mounted on it, but I don't know how it actually works - if it's a simple 12 signal, or a 5V square-wave, or what.

I've got the official Volvo wiring diagram (below), which matches up externally with the actual fan wiring I have. Red (A:1) power and Black
(A:2) ground leads going into the controller box (4/71), as well as a Violet signal wire (B:1) that comes from the ECM (either the ME7 or the Denso version depending on the car, but not both) Coming out of the controller box, straight to the fan motor are a White power (W) lead and a Black ground (CB) lead.

The ECM uses signals from various temp sensors (7/16 and 7/8), then tells the controller (4/71) what to do with the fan (6/29).

If I'm reading the schematic correctly, inside the controller (4/71) there's a resistor and transistors, and the idea is that the transistors are used to switch between three positions: Off, Low (via the resistor), and High.

My problem is that I can't figure out what kind of signal Volvo is passing through the signal wire to tell the controller what to do.

Any ideas on how I can control my fan speed?

Attached Images

	Volvo Fan Wiring.jpg (51.0 KB, 19 views)
	VolvoFanWiring2.jpg (41.9 KB, 10 views)

 

It looks very much like the Volvo controller is used on a Canbus network within the car.

Unless you have a lot of experience with Canbus communictions I'd explore another route.

 

Although looking at that diagram again 4/71 could be a simple power controller with the B:1 feed as a trigger.

If you're feeling adventurous then you could try applying a 5v feed through B:1 and see what happens. You could also try to borrow a portable scope to see what the signal along B:1 is when the fan is activated.

 

I don't have a Volvo handy to put a scope on, although I've asked on some Volvo forums if anybody's interested - no takers yet. Wonder what response I'd get at a dealership, lol

I think I might try hooking up the power/ground leads to a 12V battery, then put 5V into the violet wire like you said (via a voltage divider). If that fails to do anything, bump it up to 12V. I figure the worst I can do is fry the controller box, in which case I'll cut it off and either run it in on/off mode or fab up a ballast resistor circuit to get a low-speed setting.

 

it's probably work like this.
Volvo Fan Wiring.jpg

EDIT: try to blow 4/71 with hair dryer and see what happen.

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I'm with jumides that VO on speed controller 4/71 is an output instead of input.

The fan would switch ON automatically when temperature goes up.

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If the violet wire (VO) is an output wire, then what makes the fan come on? Something inside the controller 4/71 that's not shown - like the "transistor-in-a-box" in the middle (what is that symbol anyway?)?

It'll be thursday before I can hook it up to anything - but I'm making a list of things to try. Thanks for the ideas so far! (jumides, your english is fine)