John McGraw

I have a 65 Corvette that has an aftermarket A/C setup in it with a 05 LS2.
With summer approaching, I figured that this would be a good time to get the A/C working finally. When I fired it up, the radiator cooling fans did not come on when the compressor was energized. I am using a Speartech harness with 2 fan control outputs, but was only using the primary fan control to control both fans. I thought that maybe the secondary output was programed to turn on, but it proved not to be energized when the compressor came on either. Can other people comment as to whether their Speartech programed computers turn on the cooling fans when the A/C comes on? I have sent John an Email, but I would like to finish the job this weekend, and don't expect to hear from him until Monday. I could bring a 12v + wire from the A/C switch to the same point on my relay that energizes the coil of the fan relay and this would run the fans whenever the A/C switch was activated, but am unsure if there any negative implications of hooking an additional wire to the some point that is energized by the I/O of the ECM. I am fairly confident that this will not cause any problems, but I would hate to ruin the I/O of the ECM.

All comments would be appreciated.


Regards, John McGraw

LS1MCSS

iTrader: (18)

I'm not sure how the LS2 pcm works, but on an LS1 the pcm puts out a ground signal. I say this because you say your fan wires from the pcm weren't energized. Maybe they aren't supposed to be. Do you have the schematic of wiring for dual fans? If not, I have a good one, and it's also on here somewhere in a sticky.

ssvolvo

John,
On an LS2 ECM the computer GROUNDS the pin#86 on your relay. The 12 volts to operate the relay come from the battery positive (through a fuse). See enclosed fan schematic from an LS2 05, 06 GTO.
Please check and make sure you have a constant 12v at pin 85 of your A/C relay either with ignition switch on or off. So all you would need to do is ground the 86 pin of your relay and your fan should come on.
Also the trucks (with an engine driven fan) with LS2's have a different operating system in the ECM to operate the fan. Do you know what your ECM came out of?


John at Speartech is TOP NOTCH. I'm certain it's a simple fix.


Good luck! John

dhutton

iTrader: (1)

When I installed my VA setup I changed the binary safety switch on the drier to a trinary switch that turns on the fans when needed by the AC. I used the extra contacts on the trinary switch to energize an additional relay that is in parallel with the fan relay under control of the ECM. This way the AC system can force the fans on regardless of the ECM but only when the AC needs the fans.

Don

John McGraw

Thanks to all. Yes the PCM IO ground sinks not a 12+ signal, and no niether IO is going to ground when the A/C is turning on. I was trying to find an alternative to mounting another relay, as the underside of my dash is gettting pretty crowded, but it looks like that or sending my ECM back for reprograming are really my only two options. The ECM came out of a GTO.

Regards, John McGraw

01WS6/tamu

iTrader: (37)

I am not sure about the ls2 pcm. However, the pcm for 98-02 fcars and vettes needs an a/c request signal 12v from the a/c control panel. It also needs the three wire pressure switch installed on the liquid line from the condensor to the evaporator. After it sees 12v from the control panel and the pressure switch pressure is satisfactory it will enable low speed fans and the compressor clutch. At around 225lbs of head pressure the pcm will switch the cooling fans to high speed. The three wire pressure switch is nice because it allows the use of only one switch for both high and low pressure and the pcm determines pressure directly from it. I set it up like this on my s10 and it works perfectly.

John McGraw

I just bit the bullet and pulled the seats out and opened up under the dash. I mounted a relay that activates the cooling fan relay whenever the A/C is turned on. It works real good now, and keeps the head pressure below 190. It may run more than it needs, but it now errs to the side of safety. I mounted everything under the dash to keep the engine compartment clean, so it was a real pain, but it is now done. Crawling under the dash of an early Corvette just ain't easy for a big boy like me!



Regards, John McGraw