Just a note, wiring diagrams might not tell someone much, hopefully the service manual does though. So much of the controls on the later cars are done via the CanBus network which can't be communicated on the diagrams.
Used to be the computer needed inputs to tell it when things should be turned on, but now it just monitors the CanBus and sees the message "AC on" and so it closes the AC compressor relay. Similarly, the issue with needing the SSR (Start Signal Replicator) is due to the security module putting a message on the CanBus network that says it is ok for the vehicle to run, and until the PCM reads this it won't allow the motor to start. So now some setups require a module that replicates that same message and puts it on the network, just to trick the PCM into thinking things are ok.
I went and looked at a 2001 Ram service manual and the JTEC PCM has 2 AC inputs. The heater controls put power on a line that is branched with one going direct to the PCM and the other passing through the high and low switches before also going to the PCM. When the PCM sees power on both pins, it engages the AC compressor depending on the logic it has. This is very easy to replicate in an early car, just flip a switch and let the PCM take care of it.
I was hoping at least the NGC PCM would work similarly, but based on the pinouts it appears there are no AC inputs. So I have to guess that by then they were reading the CanBus for AC status. Not sure even where that comes from on a 2010 Ram, can't tell if there is a BCM, but I can see that the heater/ac controls are on the CanBus network, so it probably is direct from the controls. Not interested in fitting the Ram heater controls to my car, so not sure the answer right now.
My only concern with going old school is turning it off when going to full throttle. Seems like a useful feature, but maybe the original setup didn't do that so might not be the end of the world.
