"Steve B." wrote

Also realize that your system isn't a spring chicken. If something
major has gone wrong this would be a good time to look at replacing
it.

Same here, and thanks for the clarification on the terms. I just know I get
warned that the older stuff my unit has, is phasing out and getting hard to
get.

If it helps, my unit I gather shouldnt run at all now. It's 20 years old.
1988 unit install of a older style unit (kinda like buying a 2007 car right
now off a dealer). It's had decent maintenance and repair but is I gather
older than most units of it's generation lasted.