[ls1nova71]

Adding the high speed fan wiring to the PCM may or may not do anything, it depends on if it was added in the tune if the original truck didn't have two electric fans, I'm not sure what a 2007 Hummer came with. As for hooking up the A/C part. I would skip the binary switch and get a trinary switch that is made to do the job. That way, the fans wont always be on whenever the A/C is turned on. It will shorten the life of the fans having them on all the time, and as you said, you don't need them on when you're on the highway since there will be enough airflow without them. By hooking it up to a binary switch, both the compressor and fan is going to come on at the exact same time which is going to put a pretty good load on the electrical system which could cause the engine to bog down for a second whenever it comes on. However the worst part is that the fan wont be on if the pressure gets too high, just when you need it the most, because the binary switch will shut the compressor off to avoid damage, therefor shutting the fan off at the same time. If you want to skip the trinary switch, then just wire the fan to come on any time the A/C is turned on but don't wire it through the binary switch.