I have a nine year old York roof package heating and air conditioning unit. When I turn on the thermostate to start the furnace for heating there is a wineing sound but no surge of hot air. I went up on the roof and removed the panel to inspect the relay switches, capacitor, control board etc. The unit was turned on and the burners ignited but no heat. Is there a problem with the relay switches or what is the problem why no hot air? Help!

You should hear a whining sound from the inducer fan. If the burners come on but no main fan, it could be a start/run capacitor on the fan, a bad fan, a bad fan relay or control board. Can you hear the blower fan trying to start?