How should transitions from inside to outside be handled when running a circuit?
I'd use an indoor JB directly opposite the disconnect with a nipple connecting the two
Rather than trying to run the cable out exposed and then into the bottom of the box, or try to clamp it when it's going into the back, I'd put an ordinary 2½&quot; deep, &quot;5S&quot; (really just under 4¾&quot;) square metal junction box on the inside back-to-back with the disconnect, then use a nipple with sealing locknuts to connect the JB to the disconnect.  The cable for the AC comes into the indoor box and transitions to THHN wires there; these wires then run off to the disconnect via the nipple.
You can also have a general lighting/receptacle indoor branch circuit land in the indoor box and transition to THHN as well to take it outside for the serviceperson's receptacle. This is handy if your air conditioner disconnect provides that feature, and also allows you to &quot;camouflage&quot; the junction for the air conditioner behind an ordinary outlet.  Note that you may need that &quot;5S&quot; box to do this, as smaller boxes may not provide enough space for large A/C feeds.
You'll want to caulk and flash around the nipple penetration just like it was any other plumbing penetration, too, since the sealing locknuts help keep water out of the electrical boxes but don't do anything for keeping water out of the wall cavity.  The good news is that being a piece of pipe, it's much easier to flash and seal around the nipple than it would be if you were trying to run a flat-ish UF cable thru the sheathing!