Dual fan wiring problem

[xjon]

Do not know what is wrong but I cannot get the fan to work. It works when hard wired. Hook it up to an ignition wire and it blows a fuse. Hooked it up to my old fan thermostat relay (rated 40/50 A) and no go. Mckinney suggested to hook it to two relays at least 40 Amps a piece. So I bought another relay with thermostat (same one) but doesn't work either.

Any suggestions? Its the flex-a-lite 240 fan.

[NISMO_RB25]

Is it grounded properly? That is a weird problem to have.

[Joe]

hook a DVOM inline and measure the amperage the fan is pulling.

[FAST-DATSUN]

pin 30 goes to the battery + pin 87 to the fan +, pin 85 to 12v swatched and pin 86 to ground or 86 to computer switched ground and 85 to 12v constant....

[Wulfgang]

You will absolutely fry most DVM's if you put it inline with that kind of amperage. Make sure your DVM is rated for at least 50 A if you try that!

Also, don't even try upgrading the relay or fuse. That's just skirting the problem. If it blows a 30 A fuse or melts a relay then something else is seriously wrong. Those FALs should only be pulling maybe 10 A each.

[Joe]

yes that should be a given, make sure your DVOM can hold that kind of amperage lol

[wga240]

Or instead of measuring amperage directly put a 1kOhm (or bigger since this is quite a lot of amps) resistor inline and measure the voltage across the resistor? Around here we call a 1kOhm resistor an 'Alabama Ammeter'

[Wulfgang]

No, that won't work. 12 V / 1kOhm = 12 mA. The fan won't even turn with that kind of current. What you really need is a very low series resistance that can take high current, which is what a DVM uses to measure current. But most cheap DVMs are rated for less than 10 A. Unless you have an expensive DVM, you will blow a fuse at the very least.

[BoostFab]

This may be some help to you.

The schematic will activate the fan anytime the coolant temperature is above the threshold of the thermostat. The fan will also turn off when the ignition is off.

Switched 12V can come from the ignition on power.

Power for high current devices like fans should be taken directly from the battery. This avoids loading down other circuits which may not be able to handle high currents. The fuse is absolutely necessary, and should be located as close (physically and electrically) to your 12V source as possible. 30A is a typical value, but if you can get by with a smaller fuse by all means use one. You will see that we use the thermostat to activate the relay, which then switches the fan. Grounding can be any common source, but it is best to make your ground as short as possible. If you use the chassis as ground, make sure to scrape away any paint that could interfere with your connection.

The thermostat will typically have a probe that is to be positioned on the radiator somewhere.

[xjon]

I got it working but its wired to one of the wires which is in the fuse holder. I believe it is the "eng con" which was not being used. I changed the fuse to a 30 and that is powering both the fans.

I tried to wire it with the relays that is same as the diagram above. It is a Hayden thermostat relay. Just can't get that to work.

So the fan is on all the time. At least its not going to over heat.

Thanks for all the replies.