Electric Fan Swap Questions

[Curious Hound]

3 relays
No diodes needed

 

[franklin2]

3 relays
No diodes needed

One dedicated relay for the A/C? If you don't have any diodes I suppose you would have to wire like that. Otherwise power will backfeed from your fan circuit and run the A/C compressor with the controls off on the dash. Been there, done that.

I see my mistake in the diagram and it would run the low and the high at the same time. The reason I did it was if the engine was cold but the A/C was on you want the fan to run. I was trying to make it simpler but I guess I made it too simple and it won't work.

 

[Curious Hound]

3 relays
No diode needed

Or

 

[ratdude747]

3 relays
No diodes needed

Except I'm doing more than just bumping on the low speed fan with A/C use, which is what the diode does. The A/C relay adds a function to kick it up to high speed when the low temp switch closes when A/C is on. Of course, the high temp switch will always turn on high speed.

Yes, it could be simpler, at the expense of functionality (no "early" high speed engagement when the A/C is on). It's an engineering tradeoff. If I was going for absolute simplicity, I'd keep the old mechanical fan and call it a day. If I'm going to do this, I want to do this right.

 

[Curious Hound]

I believe your circuit as drawn will energize both fast and slow speeds when A/C is on. You don’t want that. Normally, the purpose for having any input from the A/C system is to make sure the fan runs in slow speed even if the temperature switch is not closed. That way you have airflow across the condenser. Thats usually all that is needed because in any other condition, the fan is already running in slow or fast speed. The condenser is in front of the radiator. So it gets the cool outside air first and warms it up slightly before it gets to the radiator. If slow speed is not enough to keep the radiator cool, then the switch changes to high speed and both the condenser and radiator get more air. Anything more complicated is not needed.

 

[RonD]

Well if you want full control.........................then add a manual cut off switch to disable the fan if you ever need to go thru deeper water
Mechanical or electric fan will soak the inside of the engine bay if either comes into contact with water

Nobody EXPECTS a flood, lol

Put a bright RED led that comes on with switch OFF

 

[Curious Hound]

Well if you want full control.........................then add a manual cut off switch to disable the fan if you ever need to go thru deeper water
Mechanical or electric fan will soak the inside of the engine bay if either comes into contact with water

Nobody EXPECTS a flood, lol

Put a bright RED led that comes on with switch OFF

I have that switch in mine. But it lights blue when the switch is closed. I just have to remember that the middle blue light should always be on.

 

[duffy]

I converted to electric this last summer, I'm using a 16" 3000 CFM fan. The temp sensor is in the radiator fins just below the upper hose (193 F thermostat and sensor set to come on at 210 F measured at the thermostat housing-reads between the "O" and "N" on the OEM gauge). I have AC and the fan only comes on when I'm sitting at a traffic light or something. Any speed while driving is enough to cool the engine without the fan. I do have a new radiator with a trans cooler in front of that. A red indicator light tells me when the fan is "ON"......but you can hear the fan come on at idle.

 

[ratdude747]

I believe your circuit as drawn will energize both fast and slow speeds when A/C is on. You don’t want that. Normally, the purpose for having any input from the A/C system is to make sure the fan runs in slow speed even if the temperature switch is not closed. That way you have airflow across the condenser. Thats usually all that is needed because in any other condition, the fan is already running in slow or fast speed. The condenser is in front of the radiator. So it gets the cool outside air first and warms it up slightly before it gets to the radiator. If slow speed is not enough to keep the radiator cool, then the switch changes to high speed and both the condenser and radiator get more air. Anything more complicated is not needed.

The relays, yes, potentially. Look at how the high current relays are arranged... in that event, the H relay kills the power to the L relay's contacts (as the L relay's common comes from the H relay's NC contact), ensuring that only the high speed motor tap has power in that situation.

That said, I see your point on the fan control... I'll probably fall back to a prior schematic with the "AC" relay removed (two relays and a diode, the "L" switch output directly ties to the AC diode and the + side of the L relay). Keeping the same high current contact arrangement since with A/C on, both relays will be active. Diodes fail less often than relays and it makes for less spaghetti wiring. I'll resketch it (or maybe go ahead and draw it up in CAD).

Well if you want full control.........................then add a manual cut off switch to disable the fan if you ever need to go thru deeper water
Mechanical or electric fan will soak the inside of the engine bay if either comes into contact with water

Nobody EXPECTS a flood, lol

Put a bright RED led that comes on with switch OFF

This is a street truck... if I'm in water that deep, I'll have bigger issues than the fan thanks to the stock intake location.

-----

Did some looking around my engine bay to get a rough idea of where I'll be mounting stuff. It looks like I'll be aiming for the RH Radiator support, as the upper rad hose and the AC cycling switch I'll be tying into are on that side, and that's where I have free metal to mount to (the HID ballast relay is on the LH rad support).

One potential issue I discovered is that while I do have an auxillary fuse box installed with open terminals (three of six used), they're for mini-ATC fuses which limits me to 30A per fuse. The question is do use two 20A fuses in parallel, or do install a single point Maxi fuse block? I'm trying to use the same fuse types already used in the stock fuse boxes... leaning towards a single maxi fuse as the Aux fuse box is only fed with a 10AWG wire (albeit a short one, it's mounted right below the starter relay).

 

[RonD]

Yes, you can combine two 20amp fuses in parallel to get 40amps, Ford does that with 2 fusible links all the time on alternators

If you can bridge the two terminals together and use 1 40amp capable wire to the device that would be better
If you use 2 wires to the device then they need to be the same length and same gauge

 

[ratdude747]

Yes, you can combine two 20amp fuses in parallel to get 40amps, Ford does that with 2 fusible links all the time on alternators

If you can bridge the two terminals together and use 1 40amp capable wire to the device that would be better
If you use 2 wires to the device then they need to be the same length and same gauge

Of course I'd use one wire... except at the very end where I'd splice two thinner wires to get my end terminals.

 

[RonD]

As long as the gauge is rated for the AMPs it will pass, its fine

A fuse or fusible link works because its "wire size" is smaller than the device wire connected to it, so it heats up and separates first, if the wire is smaller "size" than the fuse or fusible link then it becomes "the fuse" and the magic smoke is released, lol

 

[Curious Hound]

Of course I'd use one wire... except at the very end where I'd splice two thinner wires to get my end terminals.

You may not need to splice. When using stranded wire, you can strip it back a ways and divide the strands as evenly as possible. (There is often an odd number of strands in the wire) Then crimp a connector onto each group, insulate any exposed parts, preferably with heat shrink tubing and then attach each connector to its screw terminal. Voila. One wire connected to two terminals.

 

[ratdude747]

You may not need to splice. When using stranded wire, you can strip it back a ways and divide the strands as evenly as possible. (There is often an odd number of strands in the wire) Then crimp a connector onto each group, insulate any exposed parts, preferably with heat shrink tubing and then attach each connector to its screw terminal. Voila. One wire connected to two terminals.

Yeah, except the "scrap" 10 Gauge wire I'm using won't quite reach if I don't splice a bit in (per a mockup I did). The wire is from an old sealtite whip from a recovered home AC unit (I replaced the whip because the sealtite jacket was badly UV damaged, but the wires inside were still good!). Same grade wire I'd use if buying new. I have some 12 or 14 gauge wire sitting as well, which is perfect for "forking" the wire via a splice. Maybe 8-12" will get me where I need to go, comfortably. I'm good on grounds, as I'll go straight to the ground stud by the battery (with an 8 gauge wire straight to the battery). Now to find my long lost big spool of 20 gauge hookup wire...

----

Threw together a schematic of the "simplified" design in KICAD:

Hopefully this clears up a few things, mainly with how I'm ensuring both motor inputs are never on at the same time. Make sense?

 

[RonD]

Yes, that will work fine