Fan Circuit

[Payton]

Hello, I am trying to create a circuit that will run the fans that cool my engine and the air conditioning condenser on my truck. The truck is a custom project that I built several years ago and have always had problems controlling the subject fans. I have bought and used fan controllers but they are expensive, short lived, and very unreliable. Therefore I plan to try something like the circuit proposed in the attachment to this thread. If anyone knows of a better way, I am certainly open to ideas.
Thanks for your help,
Payton

 

[crutschow]

You only need one series diode from Relay 1 (left-most diode).

Any 1A diode should work.

You also should add a diode across each relay control coil to suppress the inductive transient, otherwise you'll likely blow the series diode. Connect the diodes directly across each coil connection (cathode to positive coil lead).

 

[Payton]

Thanks for the information. I probably didn't explain it well enough but wouldn't I need a diode to keep from turning the air conditioner on when I just want two fans on? In the attachment I tried to describe the four different modes of operation for the fan(s).
I don't understand about the diode across the relay coil but I think I remember seeing that on the relay cover(s) as already being there.


Thanks for your help,
Payton

 

[MikeMl]

Is there a separate way of turning on the AIR not shown on your diagram?

 

[Payton]

HI Mike,

The "Air" is controled from another switch/control. I just wanted to include the "Air" circuit just in case I forget to turn the fans on before I turn on the air conditioner.

Thanks,
Payton

 

[MikeMl]

HI Mike,

The "Air" is controled from another switch/control. I just wanted to include the "Air" circuit just in case I forget to turn the fans on before I turn on the air conditioner.

Thanks,
Payton

I was trying to figure out why the diode in that path... The diode would prevent the back feed if the AIR is turned on separately.

 

[Boncuk]

Hi,

you might omit the extra switch for air if you connect the components as shown in the attached circuit diagrams.

You have two choices: fan1 on / fan1 + fan2 + air on,
fan1 + air on / fan1 + fan2 + air on

The switch used is a three position switch with the center position off.

Boncuk