The HVAC saga continues.  Along with roofer and the unresolved (mostly ok for now but I'm still not happy) plumbing.  As a friend's grandfather used to say: You got a house (condo/cabin/cottage/insert dwelling here), you got a problem.

I learn something new each time.  (Different issues to the big old house before.)  The system is original to the design (not the condenser on the roof, though) of the building, 1964.  So it's had a good run, things were built to last and it did.  How to replace is going to be some homework, mostly for the contractor.