York Diamond 80 installed in 1996 when house was built. Short cycling (blower turning off/on frequently) in both heat and cooling modes. No apparent problem with heating or cooling temperatures. Replaced the air filter, thermostat and recycled the unit by turning power off and on. Problem persists.

When you say frequently, every 10 seconds or every 10 min?

I haven't timed it, but I would say it turns off and starts again within a minute.