gies222

I just installed an electric fan on my radiator (a push fan on AC condenser). Not sure where to hook up 12 volt source to on the fuse block. I don't want it on unless the ignition is on. Any help? I know the ignition switch is what is suggested, but that is really hard to get to. Appreciate any suggestions you may have. I have installed all new wiring on the car and don't want to cut into wires it can be avoided. Thanks

Subfixer

The fan should be powered via a relay.
Simplest installation:
Pick up the main 12V to the fan relay (Red wire) from the terminal on the horn relay.
Power the relay from one of the ACC contacts on the fuse box.

Frankie the Fink

R66

How about powering the relay from the top of your ignition resistor if you are just powering the switching and only want it on when the Ignition switch is in the on position. That way you don't have to breach the fuse block.

DUB

Not meaning to throw a stick into the works here.. But on a 1964 Corvette. It did not have nor was set up for a lot of addition electrical items to be put into the cars electrical system. Compared to later year model Corvettes that began to have all of the electrical 'goodies' put in them like power windows, door locks, power seats security systems and so on....and added areas in the fuse panel to operate these potential items.

So knowing how many amps this electric fan is drawing would concern me in how I wire it up so I am not POTENTIALLY overloading the cars current wires and their gauge sizes that were not necessary designed to POSSILBY handle this added amp load.

Also...depending on how many amps this fan draws can be putting the alternator at its limits. Which is why GM also increased the amp rating of alternators also in later years due to all of the added electrical stuff added to the cars system.

I am not saying what was recommended will not work but I look at it differently and do tests to make sure I wire it in a manner that it will not cause for a problem....regardless on how many people may have done it this way or that way....which is fine. I have to make sure I am not causing a problem regardless of any of that..

I ....myself would go DIRECTLY to the starter solenoid stud where your battery cable is attached an install a fusible link on that wire end that attaches to the starter solenoid stud. And the run that to your relay to supply the power to run the fan using the CORRECT gauge wire for this. Then I would use whatever 'switched' power source to go to the relay . and PROTECT that wire with a fuse.

Then the toggle switch or whatever you choose to switch on and off the relay to operate your fan. I would wire to a GROUND source. and then connect the wire from the switch to the last terminal on your relay.

The reason I am going directly to the starter solenoid stud where your battery cable is connected is due to the horn relay is being fed power FROM the starter solenoid battery cable stud via 12 gauge wire.. And THIS 12 gauge wire DOES have limits on what it can handle in regards to amps.. So by going to the starter solenoid stud I am taking out any problems in the cars actual wiring being overloaded....which ALL depends on how many amps this fan draws.

But THAT does not still mean the alternator may need to be upgraded but you will know that when you try it out or test it. When I test the load on the system I have everything ON electrically that can possibly be on at one time. I find the worse case scenario and test that scenario. On some Corvettes that I am wiring in addition aftermarket electrical items. The engine is running... I will operate the power seat and roll the windows down and up. have the vanity mirror light on the passenger side, have the A/C on and fan on high...have the wipers on...press on the brake...headlights on high, electric cooling fan on...basically load the system down with power usage and see what it is doing.

DUB

gies222

thanks for all the help. since i am looking for a switched 12v source., the top of the ignition resister seems easy to get to and may solve the problem. I believe that wire is a 14ga wire. Anyone see any problems with that?
I have a10ga wire from fan to relay, then out of relay to the battery with a fuse in between. Another wire to the engine block thermostat and final wire to the ignition resister 12 volt source. Thanks again for your input....

DUB

The engine block thermostat??? Did you mean the factory coolant temperature sender for the ground for the coil in the relay??? That is a ground but it has resistance on it so it may not work until the engine coolant can get hot enough to allow the ground to be great enough in order to pull the coil in the relay.

AS for the ignition source wire. 14 gauge is fine. A bit large if you ask me. make sure you fuse that wire also. You can actually go to smaller gauge wire than that due to the amount of current to pull the coil in the relay is so minor. You can use 18 gauge if you want to.

Not knowing why you are using this electric fan. IF it is so you push more air across the A/C condenser to get the high side pressures down and aid in the A/C working better. I would NOT use wire you plan on using to supply ignition power to the relay. I would use the ACTUAL wire that turns the compressor on when you use your A/C so the fan comes on when you turn the A/C on.

Not knowing WHY you are using this fan...it is hard to say due to you did not specify why you are installing it and the reason behind it.

DUB

toddalin

Actually, that's kind of backward. Under normal conditions the battery doesn't send current to the horn relay, the horn relay sends current to the battery, and your way, now it must go though that 12 gauge wire to get to the fan.

I think that the proper way to do it is to size the alternator according to the expected maximum load, and if the stock "Red" wire isn't up to the amperage, it should be increased/doubled. That way the fan gets the maximum current and the gauge still functions properly.

Chances are that if the engine isn't running, wherein the fan would draw directly from the battery rather than the relay, you probably don't need it on. And, if the fan is connected at the battery/starter solonoid, and drawing more from the battery than the horn relay, the alternator is undersized for the job and you are running down the battery.

gies222

I have a temperature sensor that operates the relay to turn the fan on at 185 degrees and then off when the engine cools down. This relay, wiring and fuse came with the fan I used. My problem is the engine overheats in hot weather in traffic with the AC on. I don't want the want the aux fan to run except when the car is getting too hot in the above situation. Just finding a place to wire the relay to a hot 12volts when the engine is on, should work everything properly. It did work properly, but after driving the car, when I parked it in the garage, the fan came on as the car heated up due to the cooling system being off. I figure that was because my relay was hooked up to a constantly hot connection even when the ignition was off. Thanks for you help.

DUB

Backwards??? I do not think so because the battery is connected to the starter solenoid and it is what is providing power to the starter....NOT from the horn relay. Because. If you removed the horn relay you could crank the engine.

The reason i know this is because I can test run engine in the frame and do not need the cars wiring to do so when the body is off the frame Thus.....no horn relay.

I have increased the size of the 12 gauge wire to an 8 gauge wire from the alternator and to the solenoid before just to be safe.

The electric cooling fan cannot run if the ignition key is OFF....as long as a relay is used to power up the cooling fan and it not being directly wired.

The fan is going to draw from the battery no matter what if all conditions are correct and the key being on and the engine not running. Connecting it to the horn relay or not does not make any difference in regards to the fan drawing power because in both scenarios. if the engine is not running and the key is on...the fan will draw power from the battery. I think you may be a bit confused in this. Or heck...I may be totally confused on thi

YES...if you turned your ignition OFF and the run was still running than the wire you used to supply power to the coil in your relay was one that was not switched power.

Understanding why you are doing this helps greatly. So THANKS in adding this added information.

I am assuming you still have a clutch fan on your engine that turns all the time when the engine is running. I have seen that when I am working on these cars when they are at the A/C shop getting charged up. When an aftermarket electric fan is installed to aid in cooling. That when the A/C is on... the high side pressure can drop a good bit when the engine is sitting there at idle when the fan is on depending on how much air the electric fan is moving When we turn the fan off...the pressure can increase. I also have huge squirrel cage fan out of commercial A/C unit that can move a lot of air adn I place it in front of these cars when testing so my A/C guy and I can see how the pressures on the A/C system are when the car is going down the road. also. I have an air flow meter so I know how much air I am forcing into the condenser also so I am not just guessing. So it can be checked adn 35 mph, 45 mph and so on.

The reason I do this is for the cars with twin electric cooling fans an NO clutch fan on the water pump....and also on the cars with clutch fans or even no clutch fan and it is fan directly mounted on the water pump.

So in come cases I can configure a set-up that will allow the fan to come on when you are sitting at a stop light at idle and when you get back on the throttle the fan can go off UNLESS the coolant temp is great enough and then it can over ride this set-up.

DUB

gies222

thanks for all the help and suggestions. Got it....now I need some hot day to test this out. Its a car for show only, so I can wait

toddalin

No, backward in the way current is routed. The alternator first supplies the horn relay and the current then proceeds to the starter solonoid and battery.

Yes, you are totally confused on this.

Ideally, the fan does not draw from the battery but from the alternator that produces sufficient current.

His intention is not to have it run when the engine is off, so connecting it at the starter/battery provides no benefit, even though it could in that scenario. However, if nothing else is running because the car is off, the existing wiring is plenty just to supply the fan so even any benefit there is extremely small.

However, connecting it at the horn relay does provide benefit when the car is running. It is closer to the alternator that is supplying the power (not the battery), and lets the gauge function as normal.

DUB

YES...I STAND CORRECTED! I had TOTAL brain fart. I DO KNOW that you can remove battery cable while the engine is running and the engine will still run due to the alternator is creating the current needed to do so. And knowing that an alternator creates more power than the battery actually has in it...logically it cannot draw from the battery due to the alternator is making more power than the battery itself has in it.

YES...it is possible that the wire from the alternator needs to be increased in gauge size and also the alternator in order to compensate for this added electrical component that is now drawing a lot more amps that was not there originally. It is possible and I often times do just that.

YES..I do know the shorter the wire of a specific gauge size ...the more amps it can handle.

Do to the wiring jobs I work on I will often times increase the size of the wire from the horn relay or junction block that goes to the starter due to I also use the starter solenoid stud to take power to a component due to I often times have to wire in numerous added on electrical component and do not want a whole bunch of wires coming off of the junction block when taking power form the solenoid area actually works better in regards to wire lengths and routing. Keep mind I also increased the size of the wire form the alternator to the junction block or horn relay also.

The reason (which is no excuse) I responded the way I did is that just the other day I was asked to map out the electric wiring out on an intense electrical job where an insane amount electronic 'goodies' are being added to a Corvette. So my head was a bit jumbled up when I got onto this thread. I apologize for any confusion I have created.

DUB