Your fan motor is going out.
Could be a resistor problem.
If you are saying the blower motor only works on the high speed setting, then the problem is a bad HVAC Resistor Pack.
if you mean highest setting being the fan speed, then the problem is most likely the fan speed resistor located in the blower motor box area
The blower resistor has failed.The blower resistor has failed.
Could be a bad fan motor resistor
More than likely the blower motor speed resistor is burned out.
it is usally a dry connection on the fan speed switch
Switch problem? Cables disconnected?
Why are you replacing the switch? If the fan works only on high speed, replace the fan resistor. There was a TSB for this.
That would be caused by the blower resistor.
I'm not a mechanic, but I do believe if you bypass the resister you will only have high speed on the fan. To that end, if the resister is your problem you should already have only high speed on the fan.
mine has the same problem........... We could use some help here............... sounds weird to me.