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Volvo fan relay and SPST safety relay

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I have seen a number of set ups to wire the Volvo fan relay for use with an aftermarket cooling fan. Not being a big fan of many of those wiring modifications or the prices to set up something more technical, I offer a cheap, easy and safer way to do this. And it works. 


I have this set up to use the low speed fan signal to a Thunderbird fan, since the climate here doesn't need more than that.


You will need: One Volvo fan relay, one SPST relay, and one in line fuse (50-70A). 


This set up permits you to wire the Volvo fan relay (+) supply line directly to the battery via an in-line fuse (50-70A). How this works is by using the ground signal between the Volvo fan relay and the fan temperature sensor. The SPST relay is installed to energize when it senses a 12V(+) signal that you can hook up to an ignition on terminal (low amp fuse), which closes the contact between the temp sender and the fan relay. Once the engine hits a temp to close the contact in the sender, it trips the Volvo relay to power the fan. Turn off the ignition and it shuts off completely and safely. No hot wires, no toggle switches, expensive solutions or the like.


If you need the high speed signal to work, just duplicate using another relay for that signal. Follow the diagram and enjoy. 


Edited by Grog

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