engine fan over-ride mod

[philndz]

I would like to make an engine fan over-ride switch so i can turn it on while the engine is turned off and the ignition is on so that i can cool the bay between autocross runs.ideas?

[Jahntassa]

I think you can do it with a relay or two.. If someone doesn't get to it first, i'll see if I can dream something up..

[russ257]

do you really have problems with overheating?

[ArcsVibe]

I would ask Madbill, I am sure he can help you out!

[philndz]

Quote, originally posted by russ257 »do you really have problems with overheating?nope.....its just a quest to cool off as much as possible. (the reason most folks will pop the hood between runs)

[MadBill]

Quote, originally posted by ArcsVibe »I would ask Madbill, I am sure he can help you out!No, electrics aren't my schtick! I work best with stuff I can see, and electrons are just too damn small for these aging eyes...

[satur9]

i may get flamed for this.but as of right now it seems like it would work(not the best but not bad either)just tap onto the wire going to the fan, to a swicth,from the battery. if the fan relay is open(fan off) youll only have one circuit if its closed theres still only one source(the battery) so your switch should overide the relay as long as you laeve it on.you could make it more complicated with interlocking relays and all.but then it will be more than 2 bucks worth of parts.

[joatmon]

There are two fan relays, both in the underhood fuse block.Fan relay one is controlled by the ECU, and turns the fan on/offFan relay two is controlled by either the ECU or by a refrigerant pressure switch.Normally relay two is open, and runs the fan motor circuit through a resistor. THis causes the fan to run at a reduced speed. if the ECU decides, or if refrigerant pressure is above 1520 kPa (220 psi), then relay two closes, and the resistor is bypassed, causing the fan to run at full speed (if relay one is closed to turn the fan on in the first place.)So, you could put a relay in line between the ECU and the two fan relay coils, and have it controlled by a switch, If you wanted to get fancy, you could run one side of the new relay coil to ignition voltage, and the other side through a switch to that yellow wire that people ground to disable DRLs,. That way the new relay would not close if the ignition was off, and also would not close when the engine was running, but when the engine was off and the ignition on, you could control the fan with a switch. Maybe the attached diagram is what I mean. No guarantee this is what you want, and less chance of it being the best solution.Turns out I found a copy of the associated wiring diagram for the fan at http://s93486299.onlinehome.us/fanwire2.jpg

Attached files

[joatmon]

that's probably overkill. it would be easier to just put a switch in line with the FAN 1 relay control wire, one position sends the signal from the ECU through like normal, the other position grounds the relay coil to force the fan on.You could also do the same thing with the temp sensor, ground the side going to the ECU, but if you grounded the line out of the ECU to the relay and forgot to switch it off, then your fan would run. If you put a switch in line with the temp sensor and forgot to turn it off, the ECU would think the engine temp was extremely hot, who knows what it's programmed to do when that happens.

[russ257]

i was watching some show on tv about deisel trucks and apparently if you turn your engine off with a turbo before it is cool thats bad. so anyway they make engine cooldown timers that will leave your engine fan running till a certain temp is achieved. you could get one of those it might work

[HamiltonAudio]

Quote, originally posted by joatmon »that's probably overkill. it would be easier to just put a switch in line with the FAN 1 relay control wire, one position sends the signal from the ECU through like normal, the other position grounds the relay coil to force the fan on.You could also do the same thing with the temp sensor, ground the side going to the ECU, but if you grounded the line out of the ECU to the relay and forgot to switch it off, then your fan would run. If you put a switch in line with the temp sensor and forgot to turn it off, the ECU would think the engine temp was extremely hot, who knows what it's programmed to do when that happens.is there not a much simpler way that wiring inline with the ECU and existing relays? I'm betting if you look close enough at the small wiring harness that runs into the fans that you'll have at least 2 wires (prolly more). My GM master manual shows only 2 wires (blk/red and wht/red). the guys above are right about the two relays and pressure switch. is it not just easier to tap into the "hot" side of the fan with a relay and be able to manually switch it on and off?this would not interfere with the pre-existing control system. on the new relay, put one side of the coil to IGN, and the other to chassis ground through a switch. thus, with key on and switch activated, you've just /forced/ the fans to turn on. in all other circumstances, leave the switch OFF and the fans will do their thing normally.thoughts?bmoney

[Jahntassa]

My only concern with that would be backfeeding into the ECU... but since the fan is probably directly connected to a relay, that wouldn't be a concern. Hamilton's idea is most likely the down'n'dirty easy no-fuss way to do it!

[cdFxer]

If feeding voltage back into the ECU was/is an issue and you really must do it that way, just add a diode inline with the line from the ECU. Get one rated for the max load the relay draws.