Reduce the size of the pulley on the motor
A squirrel cage blower is used to move air...the fan component is a large finned cylinder that looks a bit like a hamster's exercise wheel...hence the name.
The Lennox furnace filter is typically located inside the furnace unit, near the blower motor. It is usually behind a removable panel or grille.
If the blower only works on high the blower resistor is most likely the problem and should be replaced. On rare occasions if the car has blown the resistor more than once the blower motor shouuld be replaced.
replace the blower motor switch
blower motor resistor needs to be replaced
In most cases, it is due to the ventilation. Ventilation duct can be cleaned or changed. ~ Depending on your vehicle the "squirrel cage blower" may need the bearing/bushing lubricated or replaced, on some vehicles this is easy and some others very difficult. I have included (link below) of a typical blower.
Blower motor bad. Blower resistor bad. Switch bad. Fuse blown.
Same problem on mine...I had the blower motor module replaced and it works great.
Probably the blower subwire is melted and burned can be replaced 16$ from the dealer. First check the Fuse for the Blower circuit.
probably the blower motor resistor
the heater resistor needs to be replaced it is mounted in the heater box next to the blower motor
Replaced many blower modules ( in engine compartment ) from that year. Check it out.