PCM controlled AC

[jkrueger]

I have an A/C systems from North racecars in my FFR Daytona Coupe. I have a 5.3L GM motor controlled by an aftermarket harness using a Gen III 0411 GM PCM. I have been struggling for quite some time to get the PCM to control the system.

I used a 2002 Camaro wiring diagram to build the harness as it pertains to the A/C system (see attached photo). I used the 12v wire from the A/C temp controller going through a ON/OFF switch to feed the C2 17 pin on the PCM (AC request). I have triple checked all my wiring connections for continuity and that they were going to the correct pins on the PCM. I have verified 12v at pin C2 17, C2 43, and C2 18 when the relay is manually activated. I can also activate the AC compressor by manually grounding the wire that goes to C2 43 (This is how I have been running the system for the pass year). I have also verified that the pressure sensor is wired correctly and is reading a good number. Using HPtuners I can see that the AC pressure switch is showing 2.0V without the system activated. Using Mike Noonan's book "GM Gen III powertrain control systems" he suggests using a 80K ohm resistor to jump C2 14 and C1 45 to fake a pressure sensor signal if you don't have a pressure switch (I showed 1.94v in HPtuners with it connected). I did this just to try it to eliminate the pressure switch as an issue and that still did not get the system to work. I have also tried a spare PCM to no avail.

So it seems to me that the problem is: for some reason when AC is requested the PCM won't activate the relay inside the PCM to ground the wire at C2 43 which would then activate the external AC relay. There are settings in HPtuners related to RPM and TPS position that will deactivate the AC system. I have the RPM set to 5200 and the TPS to 100%, so they should not be a issue at idle where I have been trying to get this to work.

I am at my wits end and wondered if anybody had any insight in what might preventing the PCM from activating C2 43????

Thanks for any help.

JC Krueger

[jkrueger]

previous post:

I had another thought today when I was scouring through GM gen III vehicles wiring diagrams. When I got my car tuned the tuner used a truck tune to start with since it was 5.3 engine. In respect to ac system they use different pressure sensors and different PCM pins for those sensors. But the ac request and ac relay pins are the same. So if my PCM thinks it is a truck and is looking at the PCM inputs for the truck ac sensors that I don't have since I used a aftermarket car harness and wired the ac sensors according to a car diagram I can see how the ac system might not work.

I think I can change that in HPTuners, or I can get a car tune and transfer the tune over. I'm going to give that a try when I get back home this weekend.

Jc

Today:

I got it working!!!!!! WooooHoooo!!!!!

I first tried just changing the platform type from GMT800 to Fbody, but that did not work. I then used 2 credits for a stock 2002 Fbody tune and moved all my tune data over to it manually (yes that was tedious). Did a "write entire" and it now works like it should. Idle bumps up, fan comes on. Even the temp controller works.

I'm psyched.

JC

[kabacj]

This is useful information JC thanks for posting it.

John