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Posted by: simonr Aug 8 2012, 08:08 AM

Good Day, Does anyone have a wireing diagram for the relay on an oil cooler fan? My fan runs when I wire it direct. I have a 30 amp relay and I dont think I have it wired right. The oil cooler is the derale with the fan . I bypassed the thermostat on the cooler to work on it . Any help would be appreciated THanks

Posted by: kg6dxn Aug 8 2012, 08:10 AM

Try this book first...

 Relay_Book.pdf ( 1.08mb ) Number of downloads: 95

Posted by: Dave_Darling Aug 8 2012, 09:07 AM

The download fails for me, right at the end?


A relay is a spring-loaded switch plus an electromagnet. If you're lucky, there will be a diagram showing the switch and coil of the magnet on the body of the relay itself.

The switch is spring-loaded so that it normally rests connected to one of the two "output" terminals. (87a on a Bosch relay.) When current flows through the coil of the electromagnet, it pulls the switch to connect to the other output terminal--87 on a Bosch relay. The fixed end of the switch is terminal 30 on a Bosch relay, so you basically choose if #30 is connected to #87a or to #87.

For current to flow through the electromagnet, one of the terminals connected to the coil has to be hooked to power, and the other to ground. Those are 85 and 86 on a Bosch relay. It usually doesn't matter which gets power and which gets ground.

So, wiring diagram type thing:

Battery to #30.
#87 to the fan.
#85 to switched power.
#86 to ground, or to the thermostat that which gets grounded when the temp is high enough.

Using switched power for #85 means that the fan will not continue to run after you turn the car off.

--DD

Posted by: kg6dxn Aug 8 2012, 09:32 AM

Here is a link to a relay book...

http://www.dlcparts.com/images/BoschGuide.pdf

Posted by: Jeffs9146 Aug 8 2012, 12:54 PM

That's a great guide!! Thanks for posting it!!

Posted by: kg6dxn Aug 8 2012, 12:58 PM

Right!

It's the relay theory that is important. What you choose to operate with a relay is your choice.