I have a York Stellar Plus (15yrs old) with an Auto and Manual Fan Switch on the T-stat. The Fan will work when turned to ON (at the T-Stat) but it will not come on when you turn the heat on with the Fan switch turned to Auto. I have replaced the Limit Switch.
No difference
Thanks!

Could be a bad winding in the motor(ac uses high speed & heat uses low)

Could be a damaged control board as well