jkrueger

I have an A/C systems from North racecars (southern air unit) in my FFR Daytona Coupe kit car. 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.

MontecarloDrag

iTrader: (3)

In the scanner, can you see the A/C Request?
If the request can be seen in the scanner, the PCM is not grounding the relay because something is wrong. It may be low/high refrigerant pressure, wrong type of sensors or mismatched wiring.

jkrueger

When I was first trying to get the system to work a year ago I took it to a shop and had them connect a gm scan tool to the car. With that tool we could see the that the computer was getting and registering a ac request signal.

I don't think it is the pressure sensor because when I put the jumper resister in to fake the signal it still does not work unless I am missing something.

Jc

MontecarloDrag

iTrader: (3)

Ok, next test would be to use a scan tool to command the a/c compressor clutch to engage. If the wiring is correct and the pcm is good the clutch will engage no matter what the sensors see or what the tune settings are.
If it doesn't, then you have a wiring issue or a damaged pcm

jkrueger

If I am remembering right I think the tech could make the ac come on with the scan tool.

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 in the system section, 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 Thursday.

If that doesn't work I will take it back to that shop and have them connect the scan tool to it again and see if they can trigger the ac system.

Jc

jkrueger

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

Zadjaliws6

He there i need help if you can help me
Can i use
82k ohm 1/4 watt resistor for the 0.5 volts A/C pressure sensor
Because i couldn't find 80k ohm in the market i got 82k only
Thanks .

750Credit

I have this same issue on an 5.3 swapped impala. I'm using a truck tune I also have a 4l80e transmission. Is that all you did was swap it over to an f body and it worked out fine? Going to try this in the morning. Wish me luck.