York Diamond 80 mid efficiency gas furnace.
Has worked OK up to last night. Main blower will not shut off, it runs continuously. When heat is called for, all works well. When set temp is reached, gas shuts off, but blower continues.
I removed blower door, blower turns off via the door switch. If I manually press the door switch, the red light on board lights and blower starts.
Any suggestions of an easy fix?
Willing to replace parts if you suggest.
Will leave computer up and check back in an hour or two... thanks!

Hi alan, your furnace has a fan limit switch that needs checked

How to Adjust and Test Your Furnace Fan Limit Switch (http://heaters-home-heating.knoji.com/how-to-adjust-and-test-your-furnace-fan-limit-switch/)

Parttime, are you sure that unit is old enough to have a temp sense fan control? If the control board has a diagnostic light, Im betting the fan is controlled through a relay on the control board. Now, I would start by unhooking all thermostat wires from the control board and see if the blower still runs. Do this first, allan, and let us know what you find. If the blower still runs with all stat wires disconnected, it sounds like you will be in need of a new control board. This, of course, is assuming that the furnace is firing and working correctly in all other aspects of operation, as you suggest,

MGD's is on the right track, I read that as a 1980 furnace. Sorry about that.

Hey, parttime. No worries. Hard to figure these things out through a keyboard. Even the best of techs, such as you and I can only guess with limited info.

Mygirsldad77
And thank you for suggestion. I will give your suggestion a try. Will keep you updated.
FYI the model # is P4HUB16L06401A
Thanks again, alan