I took my A/C out and now I am getting the final touches done on my car and I am really concerned about overheating this engine. My secondary fan is usless now since the A/C is gone. isnt there a switch or plug somewhere that went into the A/C system that I can use to splice some wires into and run a manual switch? I really do not want to use a manual switch but if I cant get that second fan to work at all then I guess a manaul switch is my last resort. I just want the best reccomendations for the simpliest fan switch setup. I hate running wires all over my car. is it even possible to tell the ECM via the prom to turn that second fan on at the same time the primary fan turns on?

the car is a 91z28 with dual fans and a harness setup for A/C

 

what about your fan switch? That should come on when the AC isnt on. But only when it gets to a temp it will turn on, like factory fan switch come on around 220*.

 

I thought the fan switch was only connected to the primary fan and ECM

 

just take and tap into the green wire on your primary fan relay and run it to the green wire on your second fan relay and both will come on at the same time

 

how safe is that? I do not want to start a fire or anything. That would be pretty simple though.

 

Bottlefed

I've run my twin iroc fans like this for a long time with no problems, both fans come on at 224 and off at 212

 

ya but I am runninmg a 383 with 10:1 compression and 12 degrees of timing. That right there makes the engine run a lot hotter then stock TPI engines.

 

yes and Ive pulled my corvette on a dolly for about 40 miles with my trans am without it overheating and I think that would put alot more strain on the cooling system than a 383 ever would

 

The primary fan is controlled by the ECM, the secondary fan is turned on either by the A/C or by a separate coolant temp switch on the pass side head. This switch has a bit higher temp, that's why it's dedicated to the secondary fan. Somebody here will know precisely what the turn-on temp should be (maybe 230? not sure)

So if your wiring is intact, it should still work.

Or you could connect the secondary fan relay to the primary relay and have them both turn on at the lower temp dictated by the ECM, whichever you prefer.

Hope this helps.
Lou

 

Well, I am going to let it run in the driveway and monitor the temp and see when the fans turn on and then go from there. Jumping two relays to work together isnt a bad idea as long as it is safe. I dont like fires. I lost a 1991 Z28 to a fire and it sucks

 

any luck with this BottledZr28 ? i just got rid of all my a/c crap and want to do da same thing as in this post ?

 

No luck with it yet. I just ripped out the TPI harness to install a FAST setup. I am not sure how the fans will work now. I only have the primary running through the FAST ECU. I'll see how that works and if Ineed more then I will havew to run a switch for the second one

 

check out my thread about a plug....that should help both you guys out...

see ya!

 

If the fan wiring didn't come out with the tpi wiring, (ie the wiring still works like stock) your fan will still come on, without the ac. The stock fan switch will do that. The problem is, the stock fan switch will not kick on until 235-240 degrees. That is too hot for an engine like yours, and besides, most of the guys on this board have already seen the hot gauge reading, panicked, and shutdown before 240.

The simplest solution, which would not require a manual switch, is to change to a cooling switch with a lower activation temperature. 3053190 is the GM PN for a 203 degree switch that will fit. It's $20 from GMPD, and installing it is as easy as changing a spark plug, plus you wont have to hack on any wiring. Just put the old plug on the new switch The switch is between cylinders 6 and 8, on the passenger side cylinder head.

 

I moved my switch from the head to the intake becuz the headers where killing the plug. Problem is, I am no longer using that sensor now that i have the FAST setup. There was a connector labled N2O on the ECU and I just plugged it into the matching plug on a sensor that I had on the front of the intake(HSR). IIRC, the 2 sensors I have on the front of the intake have 2 different style plugs. Can someone explain what sensor I am using? The plug looks just like the one on the IAT sensor on the plenum. Its a 2 wire plug. The sensor on the passenger head was a 1 wire. Now I gotta go back and figure this fan setup again.

 

It is perfectly safe to connect the green/white stripe relay coil wires together to turn the relays on at the same time. both relays are activated by the green wire going to ground to complete the circuit. If you want to be sure you can measue the pins with the relay out. When the ignition turns on the primary side of the coil is 12 v(tan I think) the other wire will be the return. Now what is NOT a good idea is to jumper the 12v and ground together! This will blow a fuse. What is REALLY a BAD idea is to connect the larger RED wire to ground-This will burn the fusible link in the wire harness.
Didn't mean to scare you. Most burned wires are caused by shorts and bad connections. Bad connections take longer but they can heat wire and components like light sockets and dimmer switches, even a brake switch to the point of melting and causing a short.

Just a tip too=the car I just bought had both fans wired together spliced in the harness just under the fans. This meant both fans are running on one relay and it melted the relay socket. It didn't help that the splice that was made had corroded badly because electrical tape does not keep out the elements. I prefer the weather tight butt splices.