Dual relay fan fail

DUAL RELAY FAN FAIL

Painted Blue

Back when everyone was running OEM cooling fans, installing a second fan relay was a popular option to stop overheating wires and connection pins. I do think running 30 amps in a standard ?? relay pin is really pushing the limit. You may get away with it with new pins and very tight connections. The stock setup has three relay pins conducting the current of both fans. The fan relay battery input, the fan relay output and the fan fail power input pin. This is also the reason some owners have had their fan fail jumpers melt.

The dual relay setup creates the circuit so only one fan current gets passed through the relay pins. It was normally done using the fan fail relay socket rewired to use the second relay. If you want to make this modification now, you can use the light relay socket for the second relay which most have jumpered to make your HVAC lights only come on with the headlights on. This change requires quite a bit of wiring modifications.

The second relay would be wired like the original fan relay. Using the same control pin (86) circuit, a ground pin (85), a battery pin (87) and the output pin (30) going to one of the black/green fan wires removed from the fan fail socket. The original fan relay would get the other black/green fan wire removed from the fan fail socket. You will need to fuse either the relays battery input or output pins. The 40 amp breaker is fusing both fans on the fan relay output with original wiring. It?s much better to fuse each fan at 20 amps.

You can use standard relays but with my solid-state fan relays you can get sequencing of the fans on and off. My second fan relay is programmed to add another two seconds to accomplish this.

I?m currently producing a fan fail unit if you want to restore the fan fail light. It will also provide a fan running light if you use my HVAC LED board. A fan fail is an indication that one or both fans are not getting at least 10 volts powering the fan. That failure could be caused by a blown fuse or a failing fan relay.

My dual relay fan fail will require a connection from each of those black/green fan wires. It also will need a connection to the control pin going to either of the fan relays. So if you?re going start the duel relays change and want my fan fail, you may want to have those 16 AWG wires spliced into those circuits.

More data to follow as I implement this into my car.

It would be absolutely great to have something like this. My car has two VW 2-pin high flow fans, so I am definitely interested. I'm sure some swaps would be interested too.

I bought two of these fuse holders.

https://www.ebay.com/itm/363610966999

I like they can use 10 AWG wire but did not like using the cover for the hold down since it covers the fuse (traps heat). So I 3D printed a fuse block to hold the connector part of those holders. I guess I could have designed it to just accept the pins but took the quick way out. So those parts just snap into my block.

I used 10 AWG wire even though my fans only draw about 7 amps each. The heavy wire will carry away any heat produced by the fuse and of course make less voltage drop.

If your buying 10 AWG wire get 300 volt insulation or less. That way it will fit into a relay socket.

I forgot to mention that with that fuse block, the crimped wire terminal installs into the top side. You can also get that fuse block with wires already crimped and installed.

OPTIfuse has the same part. LPR-05B-10R has 10 AWG red wires. LPM-05B-10R is the waterproof version.

I have not done much. Been busy with other work. I did mount my fuse block and run the two fuse holders power wires back to the 12 volt feed though bolt. Note that bolt is a 5/16" inch.

Finished the wiring. Tested the fans sequence on and off. Still waiting for the new fan fail circuit board so nothing in my fan fail socket. I really did not need to do this other then to test the new fan fail in the car. My fans only draw around 7 amps each. If you ran new harness wires up to the fans, this setup could run 30 amp fans with no problem. I really think no one needs fans that draw over 10 amps each but maybe someone will prove me wrong.

I've got the dual relay fan fail working. I have tested it many times in my car without driving the car. I'm going to have it save any fan fail codes in ROM for more testing. That way I don't need to keep watching the fan fail light when I'm driving.

I got 3 boards so if there is more demand I will order 100 boards. The board is pined the same as the OEM fan fail socket (I'm using that socket) and put my second fan relay in the "light socket".

If you already have a double relay setup, you would need to tap into each fan power wire (black/green) and feed that signal to my fan fail. I used separate fuses (20 amp) in line to the fan relays battery power. You could fuse the output of each fan relay.

Dave your relay & fuse compartment is so clean it's a work of art!

I finished the 3 dual relay fan fails. Already claimed by 3 of us but if another owner wants one, I will order more circuit boards.

Quote:

---

Originally Posted by Bitsyncmaster

I finished the 3 dual relay fan fails. Already claimed by 3 of us but if another owner wants one, I will order more circuit boards.

---

Hi Dave, I just saw this post. I was thinking of something like this as I was going to use dual speed VW fans, do you have any more available?

Quote:

---

Originally Posted by dmcman73

Hi Dave, I just saw this post. I was thinking of something like this as I was going to use dual speed VW fans, do you have any more available?

---

If you want one, I can order more circuit boards. Let me know. I only got 3 boards, one in my car and another owner bought two.

Does this mean that you plan to produce two Fan Fail modules?

One for the two fans operated by one Fan Relay and

a new Dual Relay Fan Fail module which allows each of the two cooling fans to be controlled by their own Fan Relay (i.e. 2 Fan Relays).

Quote:

---

Originally Posted by John Rogers

Does this mean that you plan to produce two Fan Fail modules?

One for the two fans operated by one Fan Relay and

a new Dual Relay Fan Fail module which allows each of the two cooling fans to be controlled by their own Fan Relay (i.e. 2 Fan Relays).

---

Yes. One for stock wiring that uses the original one fan relay. The other is for those owners that have modified the wiring to use two fan relays. That was done before the vendors developed lower power fans. But the double relay unit has one advantage, it provides a fan fail light if one or both fan relays or fuses fail. The original wiring if the one fan relay fails then the fan fail does not get power and can't turn on the fan fail light.

To clarify the function of this:

This is to restore the function of the fan fail light when the wiring is modified to have one relay per fan, not a single relay for both fans?

There is some comments about this utilizing 2 speed fans, I dont think this is what this does. On the LS swaps for example, the low speed fan turns on at 210F (or if the AC is on) and the high speed fan turns on at 220F.

I also have had both VW 2 speed fans running off one relay for each speed for many years. Im not sure the benefit of splitting the fan relays up for single speed fans. You do need to run a new length of 10Ga wire to each VW fan if you plan on using the highs though. The existing wiring is only suitable for the lows (14Ga)

Quote:

---

Originally Posted by Josh

To clarify the function of this:

---

My dual fan fail looks at the fan relay on signal and each of the wires going to the fans. If either fan wire is less than 10.0 volts when the relay on signal is active, it give you a flashing fan fail. There are some time delays on the fan fail light built into my unit so it can work with delayed relays (to stagger the fans on and off) and not give you a fan fail light.

No fan currents pass though this unit. It just looks at voltages. So wiring you make to this unit can be 16 AWG or smaller. I use 16 AWG because it crimps nicely to relay pins.