You have to have a service disconnect within line sight of the equipment, it doesn't have to be fused as long as it is protected at the breaker panel. Breaker/fuse should be sized according to manufactures specs of unit (located on nameplate of unit- min/max circuit protection or something to that affect.
Thank you, jtrammel, for this advice and detail. Though the circuit to the compressor has always been protected by its own dedicated breaker, one contractor advised the additional sub panel with fuse was "ordinary good practice". Thank you also for the sizing detail. I will make sure that is in the final work plan, too.
The existing panel and dedicated circuit is in line of site and close the existing and future compressor. I suppose the fuse panel add-on is a "service disconnect"...but dedicated breaker allows disconnect also (in my homeowner sense).
It is particularly important that the type of overcurrent protection be what is specified on the equipment label. IF the label says "FUSES" then fuses must be used. Since most homes have breaker panels, the needed fuses would be provided in the unit disconnect.
Today, equipment often species fuses OR breakers, so you can have an un-fused disconnect at the equipment WHEN "fuses or breakers" (or words to that effect) are used on the label.
[Avatar photo from a Florida training accident. Everyone walked away.] 2 Tim 3:16-17