Tony Burbank wrote:
Outside unit just hums, dunno what tune.

Put a call in, service tech says it's the capacitor. I seen Back to
the Future, and not about to fall for a scam.

Could it be the thermostat or low on freezone?

It's easy enough to check:
1. Flip breaker or otherwise remove power.
2. Open business side of compressor unit.
3. Find capacitor(s). They look like small aluminum cans with wire plugged
on.
4. Take picture of wires and mark on chassis.
5. Remove capacitor(s).
6. Take to Graingers and say "Gimme some like this" (about ten bucks).
7. Install new.