Avoid companies like ARS. They are really good at selling new units rather than repairing them. I have an independent guy that has been keeping my 22 year old systems up and running. We're going to replace them this year, but all of my neighbors have replaced their systems in some cases 10 years ago and are looking at replacing the replacement units. It was well worth putting a couple of hundred into the units every few years along with annual maintenance rather than replacing the units.
What Sparky said - I had a good independent repair tech (Steve) who did not do new system installation and he kept my system running for 29 years. It reached a point last year where the system had an issue and he recommended that it was time to replace instead of repair. The first time I used him I had an estimate from the largest local HVAC firm to do a repair for $1200. Steve did it for $275 and the problem never recurred. I doubet I paid him much more than $1200 for several small repairs over nearly 20 years,.