Cooling Fan Installation

[cyberborikua]

Hi. Im planning on installing a new 12" cooling fan via a 4 pins relay. My plan is to hook the + of the fan motor to the 87 pin, the + of a new 87 degrees thermo switch to pin 86, an 18 gauge wire to pin 30 with an inline 40A fuse to the generator, and the negative wires of the fan and switch to ground. My question is what goes to pin 85? Not planning on using a manual switch. Thanks.

1979 Fiat Spider

[azruss]

pin 85 is also a chassis ground

[cyberborikua]

Thanks. I was not sure. 85 is the relays ground.

[spider2081]

Does your coolant temperature switch have 2 terminals ? One being connected to +12V and the other to terminal 86 of the relay??
The wires on terminals 85 and 86 carry only the relay coils current and #18 is more that adequate. However # 18 wire for the fans operating current on terminals 87 and 30 is too small for a 40 amp circuit. I think you need a #10 wire for a 40 amp circuit. Also what is the maximum current rating of your generator. Are you sure your generator is large enough for the additional load of this fan??
If it isn't everything in the car could be operating at a lower voltage when the fan is operating.

[cyberborikua]

Switch has two terminals. I have the stock generator. Question: Isn't the use of a relay help with the generator load? Can I then use the coil instead?

[rridge]

The original Fiat electric fans drew less than 10amps. I would check the amperage of your new 12 inch fan. Most Bosch style cube relays handle 30amps or less. If the fan is less than 20amps, 12 gauge wire would handle the load.

Size the wire and the relay to the load. Size the fuse to the wire. Don't use a 40amp fuse on a wire that can only handle 20amps.

[cyberborikua]

Got it! Looked at the fan and see that it is 80W. That is 6.66 amps. All the wires in my relay are 16 gauge, not 18 as previously stated. The relay is a 30/40A. So can I just put a 20A fuse on the 16 gauge wires?

[rridge]

I use 10 amp fuses on 16 gage wire.

[Sparky]

relay > wire > fuse > load

For efficiency, it's good to have relays that are rated well above what you're drawing through them, similar with fuses, that way they only pop when you have an actual problem and not just when the car is hot or when subjected to the motors in-rush current.

With new wire you can easily run 20A on a 16awg copper wire, even in the engine compartment (unless you're using wire with really lousy insulation). Eg. if you're running high-strand-count silicone or teflon jacketed wire, you can pretty much double the ratings you find on most ampacity tables, while if you're running the original wiring from the 1960's or '70's you should probably de-rate the tables a bit further.

A 15A fuse and a 20A+ relay with 16awg wire should be more than adequate.

[cyberborikua]

Thanks Sparky. Im still confused with pin 85 or 86. I know one of them goes to the thermo switch. Lets say, i connect 85 to the radiator switch, does 86 go to ground? Im looking at cooling fans diagrams online and some indicate to jump 86 to 30 while others send it to an ignition 12v source. A few indicate 86 to ground.

Im looking at the easiest, yet effective way to do it. Any help is appreciated. I now know my relay wires are fine, just need the proper wiring.

[Sparky]

So there's lots of ways to wire a relay, the important part is that you energize the relay with your low power circuit to close the high-power circuit.

The safest way to wire it up is to run your original, fused, ignition activated fan power to 85 or 86 (in this diagram), it usually doesn't matter which way the current flows through the coil. The other side of the coil goes to your coolant switch and the other side of that switch to ground. Then you can run a heavier wire with an inline fuse from your desired power source (tapping onto the positive ring terminals on the back of the alternator or starter) to pin 30, then from pin 87 to the positive side of your fan, and ground to the other side of the fan...

You can make the whole thing more compact by skipping the ignition controlled circuit and running power from the source to pin 30 and the coil. This means that your fan may stay running after you park your car (good for hot running cars, potentially bad for your battery).

[spider2081]

The safest way to wire it up is to run your original, fused, ignition activated fan power to 85 or 86 (in this diagram)

I think on a 1979 Spider the light blue wire at the stock fan is fused from fuse #10 and is "Hot all the time" meaning the ignition switch need not be on for the fan to run.
I believe the original wire used by Fiat was a #12 and the fuse value was a 16 amp for the 79 Spider. Earlier Spiders might have had the fan powered through the ignition switch so it ran only when the switch was in the "start or run" positions. I think it is common most cars coolant fans can operate after the car is turned off. Usually it will only cycle on and off a few times.
I think Fiat found it necessary to change the fuse from an 8 amp to 16 amp because the "start up" current for the fan was much greater than the "run" current.
I am not sure there is a cooling advantage installing a fan that draws approximately the same current as a stock fan.

[aj81spider]

With new wire you can easily run 20A on a 16awg copper wire, even in the engine compartment

The wire has the capacity to handle the current. However another consideration is resistance and voltage drop. 16 AWG wire has 4.43 ohms of resistance per 1000 feet at 25 C (and 5.29 at 75 C - say inside an engine compartment). 12 AWG wire has 1.68 ohms at 25 C.

If you are drawing 20 amps of current through 10 feet of wire that means with 16 AWG wire you will drop 0.9 volts in the wire. With 12 AWG you will drop 0.33 volts. The lower voltage drop means more voltage (and power) delivered to the load and less heat dissipated in the wire.

In general you are better using bigger wires when it is practical.

[cyberborikua]

My 79 already had an aftermarket fan with the stock's thermo-switch when I bought her. However, I installed a new stock-like radiator (original one was leaking and in bad shape), a new 12" fan, and an 187 degrees thermo-switch. I installed the new fan and the switch following the same wiring on the previous relay. The car had never overheated until recently when I got into a traffic jam and it went to over 200-220ish while idling. It was not until then that I noted that the fan/switch setup was not working. I still have the same relay wiring setup and I think everything looks good and should work. Pin 30 is hooked to a thick yellow wire but another thinner wiring that is running parallel to this yellow wire is hooked to pin 86. The new thermo-switch I connected to 85 and the fan to 87 with the black wires going to ground. Still nothing happens. Is it possible that the relay is bad? I tested it with 12V and it clicks. I have not tried for continuity between 30 and 87 yet because I don't have a multimeter. Also, the fan has two wires, black and blue; the thermo-switch has two wires, black and grey. I am assuming that both black wires are ground and the blue and gray wires are positives. If I am wrong, please let me know.

[cyberborikua]

Got a multimeter and a crash course online on how to use it. Tested the relay previously installed and is all good. However, tested the wire on pin 30 with the ignition on and the voltage was less than one (0.56). Followed this yellow cable and found it was welded to a green cable that disappeared into the dash. A lower gauge wire on pin 86 was actually jumped and welded to the green cable on 30. I don't think that setup was working with no juice on 30.

My plan is to discard that setup and try a new one. Im planning to use the current from the generator for pin 30 and jump 86 to it. Switch to 85 and fan motor to 87. Both are already grounded. The generator gets 12V from the ignition so the fan will turn off when the car is shut off. Right?