A properly operating A/C system is closed loop and should never require recharging unless there is a leak.
You could hook up a pressure manifold to check pressure, but if you find it low, the source of the leak would need to be found/repaired or a recharge would only be temporary.
If you put a thermostat in your center vents and turn your system on max, the air should be 20-30 degrees F below ambient.
In the service manual, there are different charts for the high side and low side pressure ranges at various temperatures. Someone who has a SHO manual should be able to post them up. I'm guessing my Explorer may be different, since I have a much larger system capacity.
Hope this helps!
EDIT: Is your AC compressor coming on? If system pressure is too low, there is a failsafe that will prevent the compressor from engaging. I'm not sure what the threshold is, though. My 2013 had a line leak and leaked everything out. I had to remove the AC relay and jumper the connection to turn on the compressor for charging.
FORSCAN can be used to check the status/commands in the system, but I'm not aware of a pressure reading in the system. I just used an external gauge set.
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