Mandic

I just wrapped up a 5.3L swap in a 1998 C1500 Silverado(originally a 5.0L truck). After getting a few bugs worked out, I simply cannot get the AC to turn on. I am running the 5.0L ECM to power the gauges and the AC system and it just isn't commanding the AC relay on. I can ground the AC relay and get the AC on, so my clutch power circuit is solid. I jumpered the original high pressure switch and am getting AC Request signal to the ECM. I have tried jumping the Low Pressure switch to ground, and it just will not turn on. As far as I can tell the AC Cycling switch(That used to mount to the manifold lines) is a normally open switch. No matter what combination of these switches I cannot get this AC to fire up on the truck's command.

Does anyone have an opinion on what I am missing? Is the 5.0L ECM just not having it since it doesn't detect a running engine? I read a few write ups on these swaps before I undertook this project and no one mentioned anything special with the AC other than letting the stock 98 ECM control it.

Lextech

iTrader: (18)

There is NO reason to run 2 PCMs for your swap. With a little bit of wiring rework and the addition of 10 wires, you can use your 98 5.0L harness to run the Gen3 engine. PM me your name and e-mail address and I will send you some A/C wiring info to try to help you out.

Jeff

Boomer MN

In regards to the question on running 2 PCM's and AC:
SandP has a write up on their site claiming this is the way to go. You let the old PCM control the brakes, AC etc and the new PCM cotrols the new LS motor.
So??
Bill
Confused in MN

Lextech

iTrader: (18)

I replaced the Black PCM in my 98 truck and have been running the 12200411 LS1b PCM for about 6 years now. I don't know why SandP does it like that. Here is a link to the PCM swap. GM Truck Central GMT400 12200411 PCM Swap

Jeff