FART_NUGGETS

I've searched around and checked the sticky threads. Please don't delete me

I'm not running AC in my car but it had it from the factory. 89 Iroc with 305 TPI and dual fans.

Like 90% of us my car gets hot in traffic, in a drive thru, etc.

I was looking at the wiring diagram I found for the dual fans and I see that they second fan only comes on if the AC system has pressure (wont happen in my case) or the coolant hits almost 240 degrees (I'd rather not check).

I tapped into the green wires on both fan relays and jumped them together. Started the car and waited for it to hit 220, and when it did, both fans kicked on and the temp pretty quickly came back down.

But the fans never shut off. They ran continuously, and the coolant actually got to the point on the gauge just below the mark between cool and 220, where it usually rides on the highway.

If I cut the jumper wire, the fans would then both shut off.

I am guessing that once the ECM kicks the fans on, the ground is backfeeding through that second relay and making the ECM think that the car is still hot. After experimenting with some diodes to try to stop the backfeed, I ended up just snipping the green wire to the secondary fan relay in the harness. Once I did this, the fans both kicked on and off as expected, just both of them at the same time.

This seems to be working excellent, as once the fans kick on, the temp very quickly drops. With the single fan, It would just hover at 220 and I would be praying it didn't overheat on me.

Going to run a tap to a hidden toggle in the dash so I can flip the fans on in traffic and leave them on.

Any issues with what I've done here?

Tootie Pang

iTrader: (2)

I would guess the reason they stay on is once you jump the two together and the first fan comes on, the tied green/white wires lock in the AC Pressure switch or High Coolant Temp Switch (-) input to the ECM via the Gray wire. The ECM then turns the primary fan on by grounding the green wire for its relay, which, since the greens are tied, then feeds back into the AC Pressure or high temp coolant switch input to the ECM.

FART_NUGGETS

Yeah that makes perfect sense.... I was putting the diode in the wrong place (was placing between the fans, needed to go on the green wire to the second fan so as to not backfeed the ground back to the ECM.

This is working well as is though, since I don't have AC this is a quick way to get both fans to switch on together instead of waiting until ~240 degrees for the secondary. Might pop in a lower temp fan switch on the passenger head (190 or so), even 220 degrees is a bit too warm for comfort for me.