crowtree99

iTrader: (1)

Hello everybody, hope somebody can help here!
I have a 1969 chevelle with a 2001 ls 6.0 lq4 in it complete with the factory pcm and wiring harness, the car has aftermarket vintage air ac which is my issue.
what should trigger the pcm to turn on the cooling fans once the ac is turned on?
All my data shows an ac request of 12v being sent to pin 17 which I have but no fan output?
I have verified both fans work and both come on through the pcm at the correct temperature points.
Am I missing something or is it a different pin?
As you can guess once the ac is turned on and no airflow from any fan the head pressure is very high and probably the reason the compressor was dead when I acquired the car and after replacing and recharging I want to make sure there is no repeat of that!
So any help or direction to chase would be great.
I know I could use the 12v to trigger a relay to trigger the cooling fan relay but that would be last resort as would prefer to make it work the factory way

mantycarguy

The factory program in the pcm was probably not set up to run the fans as most of the truck engines used mechanical fans. A good tuner should be able to remedy this for you.

crowtree99

iTrader: (1)

You are absolutely correct and I guess I should have stated this in the thread to start with.
My tuner ( Doc at EFIAlchemy, Green Cove Springs, Fl) has already been through the program to set and check fan turn on temps and verified that it is set up to turn on the fans on ac request.
So we are still missing something...probably simple and obvious but I do not want to start putting voltage onto pcm pins with a random guess....
Thanks

flame

iTrader: (13)

I had a quick look at the wiring and there is a high pressure recirculating switch that you would need to ground pin 11 on C2 to make the pcm think there is high pressure to turn the fans on

crowtree99

iTrader: (1)

you know I started to have this feeling I might need a ground somewhere after reading some likewise fuel pump relay issues elsewhere but did not want to start just poking pins.
Sounds like a good plan and will give it a try when I get back home from Texas.
Would that be a regular electrical ground or a pcm ground do you think though?
Many thanks!

01ssreda4

iTrader: (96)

Ever considered manually wiring it up? As in your ac trigger Ts off and goes straight to the AC fan relay. That way both come on at once.

crowtree99

iTrader: (1)

i have but would like to figure it out, bugs me more than anything now, had one suggestion that I need to ground pin 11 to make the pcm think the ac system has high pressure which should work too
many thanks