aux cooling fan ac pressure switch

so i got my new hoses installed and system charged. ready to turn on the ac but i need my efans to kick on high speed durring operation. Im looking for the best way to do this.

a few options are...

1) hook ac control wire to PCM
- This will have to be done after i find someone with the correct software to change the pcm port to discrete instead of class 2 data. so this option is out for now

2) hook ac control wire to a relay. that realy when actuated will supply a ground to the relays that the pcm would normally supply a ground to for high speed operation

3) using the aux cooling fan AC pressure switch which is in the condenser already. from the drawing, it looks like it just supplies a ground also. which would serve the same purpose as option 2 but with a heck of a lot less wiring and one less relay to add.

but im confused on how that switch works. im assuming when the ac pump is engaged and pressure starts building, this switch closes and will kick the fans on??? does it cycle on and off? should my fans be running on high constantly as long as the ac is being called for reguardless if the pump is engaged or not?

and why do i have this switch in the condenser but my truck originally came with a clutch fan and there is no relay for aux fans in my fuse block...??? did GM really install it for a "just incase" upgrade or is this switch something completely different?

http://i18.photobucket.com/albums/b1...page-001-1.jpg
this is the switch im talking about
http://i18.photobucket.com/albums/b1...ans_rodder.jpg
and this is how i have the fans hooked up now. ill just need to tap into the wire coming from pcm to the two high speed relays. i will also install a diode to prevent backfeed to pcm.


not sure the best way to do this. thanks.

I don't consider myself much of an expert so don't take my advice too serious lol i would definetly try option C if possible and I would see how that switch works on the condenser by using a voltmeter and seeing if that switch makes continuity to ground when pressure is detected in the condenser? Also at what psi does that switch close? Is it more than what static pressure might be on a hot day? Idk it does seem like the easiest route but only If that switch works the way you want it too

thanks for the reply. i spent hours on it yesterday trying to figure out what i was going to do. i did like you thought and ran the pump while checking the switch to see if it made contact before and after. i couldnt see a difference.... so i gave up on it and bought a relay. i wired it all up and it still didnt work... but i checked a few things and saw that i didnt wire it correctly. but i know what i did wrong. ill have to end up changing a few wires but i think i can make it work.

i still dont know what exactly the switch does on the condenser... but theoretically as long as i straighten the wiring up, it should do what i want it to do... once i get it working, ill post a modified diagram with the relay in the circuit in case anyone else wants to run a setup like this. ill be out of town until tuesday... so hopefully wed i can get back on it. this is really bugging me since im so close to having ac for the first time in 5 years... lol

'Jay, check out this from Brendan at LT1 swap. Shows what you may need. You may have to change a few wires around. Seems easy enough.

Scroll down to about 3/4 of the page. Hope this helps.

http://www.lt1swap.com/wiringharness.htm

thats exactly what i was talking about and how i intended to hook it up. but i miswired a few things which i know what i did. i just havnt had a chance to fix it yet with work and all. hopefully mid week ill be able to get back on it. like i said ill post up the results. thanks