The fan limit control is there above the right hand side of the furnace, pretty much where it is positioned in this image....
I'm off now to check out, and post a pic of the room thermostat. It's another 60 year old girl with a mercury switch inside of a coil. If I recall it does have a duration adjustment. I'll post a pic.
Meanwhile I removed the gas burner to see if anything needing cleaning or adjustment.
It's a good thing anyway that I looked into the burner since every nut and bolt in the thing was finger loose and worse.
Everything looks good on it.
Here's the room thermostatinternal adjustment...
Here is an image grab from the user's manual on this thermostat....
My heating type is "Standard warm air" so it would appear that the setting is pretty much as intended. Should I raise it in .1 ampere increments to see what happens?
I really hate it when directions aren't more explicit. When they say "furnace shuts off before" I wish they would have merely included the "furnace burner
" qualifier for the sake of unambiguous clarity.