Triple beat me to it. If everything's grounded properly, the disconnect's housing would be hot if the RTU cabinet was no matter how far away it was mounted.

And if it's right on the unit, The HVAC guy (That's usually me) never has to wonder if he's turned off the right switch. And do us a favor, mount your switch right above the equipment's data plate. When they're exposed to the sun and rain they fade so bad we can't read them but everytime I see a data plate under the disco, the plate looks like the day it was made. [Linked Image]