re: How often do your home a/c unit(s) break?

Almost never. Both Trane units, one from 1995 and the other from 2006. Serviced and cleaned every year, only one needed a slight top off on refrigerant this year. I check the capacitors and have my own testing equipment to check for anything showing signs of weakness or a motor drawing more current than it should. Replaced one capacitor as a precaution this year for all of $20, keep several spares on hand.