Intermittent fan blower on heat, cool, and off

Fan will run on odd time increment (6 seconds on, 1 min off, 2 hrs on , 3 min off, 20 sec on, 1 day off 12 hrs on etc….). Does this on heat, (satisfied stat) cool and stat turned off. Indicator lights normal. Clean filter. In summer and winter. No literature on this. 3 yrs old york. Very frustrating. Have to turn off main power at times to stop it because sometimes it will run for days, then be off for days all the while the stat is off.