The fan on my York furnace comes on for a while, shuts off for about 30 seconds, comes back on and runs for a while, shuts off and then comes back on, then finishes it's cycle. Any ideas?

How old is the furnace? Is it the draft inducer fan, or the blower fan that kicks on and off? Go to the unit and see exactly (and in what order) is happening and let us know.

The furnace is about 10 yrs. Old, was in the house when I bought it 8 yrs. Ago. The draft inducer comes on, then the burner comes on and it heats up like it always has, then it starts doing this on and off cycle thing with the blower fan.

Sounds like its either your blower motor, capacitor, or the fan relay on the control board. Check the capacitor. Check for power going to the motor when it cuts out. If the motor is still receiving power when it stops running, the motor or cap is bad. If you loose power to the motor when it cuts out, you most likely will need a new control board. Please let me know what you find.

My Daughters new boyfriend works at a heating and cooling company. He came over on this past Saturday and checked it out. Everything checked good until he got to the thermostat, it was full of dust. Blew it out and it's been working like it always has. He had never heard of dust in the thermostat doing that, but there is always the first time I guess. Thanks for the help.

Yep, that's a new one on me, unless this is an electric furnace? Usually the fan is controlled in the furnace itself during a call for heat. So as long as the stat was telling the heat to kick on, the furnace fan relay/control would then tell the fan to kick on or off. But like you said, there is always a first for everything. The good news is, you have a tech in the family, so if the problem comes back, maybe he can catch it in the act. For now, Im just glad its working correctly for you. Take care, and thanks for the update, I really do appreciate that.