I recently moved into a house my wife and I purchased this summer. When I went to turn on my furnace a week ago I noticed the problem. When I turn the furnace on the burner will fire up and the powered exhaust fan comes on but the main blower will not and the furance will shut down once the high temp limit is reached. The relay is making quite the noise when I turn the furnace on and if I tap on it the sound will stop but not all the time. To me it sounds like a bad coil in the relay but what I don't understand is why the blower works fine when I run the A/C. The blower will come on and go off normally while I am running the a/c but not the heat. My furance is a York Stellar that is 15 years old. Any thoughts?

Sounds like you have a bad relay, if the relay is attached to a printed circuit board then the board would need to be replaced, this furnace may have a separate relay for heating and air conditioning. Good luck, Mike