I will be in to about 10 pm tonight, then back all day tomorrow.
There are several things that will cause the blower to stay on at all times.
- a bad printed printed circuit card, fan relay contacts burned closed. (70% chance at this point)
- The furnace high limit switch is tripped, the card programming runs the fall all the time in that
case to insure the furnace does not over heat, (20% chance)
- Flame roll out switch open, 0 to 5% chance.
Please attach a well focused, close up photo of the wiring diagram glued inside the service panel,you can use the paper clip icon at the right end of the toolbar at the top of this dialog box,Include a picture of the thermostat wire connections to the printed circuit board in the same area.
If there is no paper clip icon, look for the '+attach files' link at left of your send button.
I can mark up the wiring diagram with trouble shooting instructions.
You can also perform a heat stress test on the printed circuit card..it is about 70% reliable.
Use a hair drier to slowly and gently warm the card to 120F(warm to the touch but not hot and not over140F)... if you get any change in behavior that means the card is bad...
A micro crack has opened in the printed circuit at a solder joint, or inside its CPU in that case .... or a short circuit has developed as the card expanded when you heated it.
Constant expansion and contraction as these electronics heat and during their duty cycles over the years is what wears these cards out.
It is also a good idea to replug all of the connections in the unit,that burnishes any oxidized terminal connections and will sometimes solve the problem, especially at the printed circuit card and in any sensor molex connectors. Do that with the power off to the unit of course.
We can go from there.