trader_4 wrote:

Why they don't make the new encased,
insulated evaporators with a removable panel, IDK. But I've seen a
few, eg Rheen, Lennox, and no access panel.

When I replaced the 25 year old system here, the coils were still clean,
looked fine. And that was with just one of those cheap 1' thick fiberglass,
minimal filter. New system has a 5" thick MERV, so I'm not worried.

You've answered your own question: the only time you'd need to clean it would be
if soot had been drawn into the system. And if that's the case, you've got
larger problems.