Could use some clarification on obs swap

[93fs]

I've been poking around on the forum for awhile now and have found some great info. But I figured it was time to finally make a profile and try to get a couple last questions answered before I set the engine in. The truck that's being swapped is a 93 c1500 RCSB, and the engine/trans is an 03 lq4 and 4l80e. I'm going through psi for the harness. I'm going to use the factory ac compressor from the 93, where some of my confusion comes in is how to tie the factory ac into the new harness. I see that psi has an option for AC recognition. I assume I need that? And once the engine and new harness is in, do I leave the factory 93 pcm in to run the compressor and switch? Or is it only controlled by the hvac control on the dash?
Next question is fans. I hate the clutch fan so I bought a used set of ls1 f body fans. I see that psi also offers fan relay harnesses. It looks like I'll need two of those. And once I do, will it be as simple as hooking the two ground wires of the relays to the harness? Or is there more to it than that? Also I'm switching to a DBC throttle body and 411 pcm if that changes anything.
I was hoping not to be the guy that bombards the page with questions on the first post but these little details have me a little nervous about the swap. And I'm hoping someone else on here has gone through the same issues. Thanks in advance.

[super10brss]

From my understanding: You have a ecm (engine control module) that runs your stock motor (that will go away) and a BCM (body control module) that controls things like your AC. The "easy" thing about the LS swap on our trucks is the AC system just does it's own thing from the BCM (that will stay) and you do NOT need the AC request from the LS computer (from my research). That is if you use the factory R4 compressor, which seems to be a no brainier, all the wiring/hoses just stays in place. All you need is a R4 ac bracket for the LS engine. There are lots of options out there, but I plan to use the Holley one https://www.holley.com/products/acce...y/parts/20-133 Again from my research people say that it is the best factory like that doesn't squeal and get off line dropping belts etc.

In regards to the fans, I am not sure on that one. I apologize (and don't want to give bad info) I plan on "trying" to retain the LS manual fan. If it cools the LS in the truck/suv it came out of it will cool the engine in my 1989 truck. My goal is to keep it simple (besides the fact electric fans will pull more power with a heaver reliance on battery power.)

[super10brss]

One more link that may help you 93fs http://www.ls1truck.com/forums/lsx-t...-help-you.html

[93fs]

Thanks for the response, and assuming the info for the 94 in that link is the same for a 93, that helps clear a lot up as well. I already have the dirty dingo ac bracket for the factory compressor. Didn't see some of the mixed reviews until I already had it so I'm just hoping for the best with it. And in regards to the stock pcm, I know it wouldn't really hurt to leave it hooked up and in place after the swap, but I mainly just didn't want to acedently kill power to it when I start eliminating the original wires.

[brianmcb]

My 95 runs perfectly fine with the stock obd1 computer totally unplugged except that it throws an ABS code and lights up the dash. I'm sure your 93 doesn't have abs so you should be able to completely eliminate the factory ecm.

I'm running a dual speed electric fan on my truck. Some sort of Ford fan. Cools my cammed 5.3 perfectly fine with the stock single core 27" radiator. I've idled it in traffic here in hot 38 degree weather, temp drops quickly when the fan kicks

[93fs]

Cool, yeah I figured the F-body fans should be fine, they cooled my lt1 car perfectly fine, and the radiator design on those are awful lol. Brianmcb are you running factory ac?

[brianmcb]

No ac on my truck.

[farmtruc]

The nice thing about having the ac compressor pcm controlled is the engine will adjust according to the pcm parameters when the ac clutch is engage/disengaged.

[1991SSP]

On my 94 model swap I used a standalone harness from nelson... I left all the factory engine bay wiring in place... AC system operates like it did from the factory...the plugs that were not used I snipped off, taped up the wires and put them inside the loom..