I am trying to troubleshoot my 43 year old (yes, really) AC Delco natural gas furnace. It is a huge furnace in a closet in my hall bathroom. I had the thermocouple replaced last December. The new problem is that now, when the temperature reading reaches the set point of the thermostat, the gas jets shut off, but the blower does not shut off. I have to manually turn off the blower with the wall-mounted on/off switch, which looks like a light switch. Can anybody tell me where to find a temperature sensor, or whatever part seems to have failed? Thanks, Candace

Its in the center of the furnace above the burners

There is a good chance it is the relay too. It will be near where the electric power goes into the furnace. Follow the wires to the blower back to it.