Getting A/C working with a 2003+ motor

[downtowncb]

Ok, I have a 5.3 from a 2003 Silverado. I'm working on the harness and I'm trying to figure out how I'm going to wire the A/C. As I understand it, the ECU receives a signal from the BCU over serial and turns on the compressor clutch. My question, is there another way to directly signal the ECU to turn on the clutch? Otherwise should I just power the clutch directly? I'f possible I'm trying to make A/C switching seamless. Thanks.

[GasGuzzler]

Need to know what the engine is going in.

[downtowncb]

It's going in a '98 Grand Cherokee.

[GasGuzzler]

Oh crap. No wonder you didn't mention that.

Are you using only the Jeep body and all GM computers and wiring? If so, I can help...maybe. If you're using just the engine and all Jeep crap I'm out

[downtowncb]

I'm using the Chevy engine and ECU to run it, otherwise I'm keeping all the Jeep stuff. Is there any way when I reprogram the computer to enable the old A/C request on one of the pins?

[GasGuzzler]

All depends on how AC request is accomplished by the Jeep controls.

[downtowncb]

The A/C request is currently accomplished the same as the older style chevy's where +12V is applied to a pin on the ECU. But since this newer computer uses the serial link I'm trying to see if the old manner can be programmed in when I have it tuned, or if there is another way to generate the request without the BCU?

[GasGuzzler]

OK...I see your point.

On the 2003+ HVACM sends Class2 data message to PCM requesting AC. As long as pressure sensors are in parameter the PCM grounds the compressor relay.

The 2002 works the same only the request is 12V from the HVACM to PCM C2-17 through AC pressure switch.

You could get a custom tuned 2002 PCM or possibly have that pin "turned on" on a 2003 but that's over my head.

Let's see what that pin is on the 2003 PCM....

Aha! C2-17 not used on the 2003. Might just work but someone familiar with tuning needs to chime in and see if C2-17 can be made to receive 12V AC request AND enable the compressor relay.

Long shot...