I have come across a few comments saying that the ECM turns off the A/C under WOT conditions. This is not true. The ECM really has no way of doing this. It can only see if the A/C is on, not control it.
Just in case you leave it on at the starting line thinking it turns itself off in the quarter.....

J

 

Why do you think gm put crap like that in the code?Does'nt even the new ac systems work the same way,no input from pcm?

 

Because that is what software engineers do......over-complicate things.

J

 

Usually it's because they're trying to workaround the problems that the mechanical engineers create. :P

 

which usually means it gets dropped into the tech's lap.....

 

The 730 does turn off the AC when WOT, just not in a third gen F-body V8 application, FWIW. When used in a V6 car, the ECM controls the ac via an ac clutch relay. I have also seen this in Berettas and such. Maybe it is used in Corvettes in the 727 but I don't have a diagram in front of me to say for sure.

 

So the saga continues. Please explain how an input can control a relay.

Or is there two wires connected to the relay? Don't let the wiring diagrams fool you. Have you verified the A/C turning off visually?

J

 

On a 730 v6, yes, I have seen it personally. On a v8 730, no, the ac is not controlled by the ecm just as you stated. However, I did look at a Corvette with 8D and 727 and the ac is controlled by the ecm. This is why the the 8D has the ac code in it. The way it works is simple. AC request is an input to the ecm as well as other AC components. The ecm does a check and puts out ground to a relay. The relay puts out power to the high and low side pressure switches and if all is good it reaches the AC clutch. This in turn also makes it back to the ecm for fan operation. SO if you wanted to make the AC be controlled by the ecm on a 730 v8 F car you could run the Vette code and figure out the I/O pins and use a relay to control the clutch.

 

Can someone please post the ECM pinouts from a shop manual of a v6 car that uses the 730. So we can see which pin is grounded out at WOT to disable the A/C clutch.

 

OK, you're not understanding the way it works. As already stated, the V8 730 does not use the ecm to control the AC clutch. It uses an input from the AC to tell the ecm when to do certain things with idle and fans. The actual control of the clutch is completely seperate from the ecm. On the V6 and the Corvette 727 app. it is the ecm that puts out a ground to the relay which puts out power to the pressure switches that finally reach the ac clutch. The way the ecm does this is completely different from the way it is in the 730 V8 app. so there is no wire to add. You have to run the Corvette code and figure out the pins from the 727 to a 730. Then you can rewire the harness for AC operation by the ecm. On the V6 730 the pin for AC operation is used for the upshift light on a V8 730 manual trans. The pin is F1 just in case you wanted to know.