Can I use exposed UF instead of THHN in conduit to outdoor AC disconnect?
UF cables can be installed outdoors without being in conduit unless it is somewhere where it could possibly be damaged. So no, it can't just be run plain to a disconnect and tacked to the wall. Any decorative PVC would have to be strong enough to provide protection for the cable. The same goes for the run from the disconnect to the compressor unit as it could definitely be damaged. Since it's hard to run UF in conduit, you'd be better off just installing the conduit and pulling individual conductors.