It would have a high speed relay and it would be in the power distribution box under the hood. The blower speed resister is for the lower speeds only.
The heater motor speed resister is burned out.
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.
The most likely problem with the heater blower on your 2003 Sable is the blower resister. The resister can go bad and cause you to only have one speed.
Probably your blower motor speed resister is burned out.
You have a bad blower motor resister.........
I would suspect the blower motor speed resister is shot.
All BUT high speed runs through a resister panel to control the speeds on its own circuit. High speed is direct on its own circuit. High speed works so that circuit is good.I would check the power to the resisters.I have replaced a few resister panels on various vehicles do to this same problem.
The blower motor speed resister is burned out. This part is available from your local auto parts store.
The blower resister could be bad, or the blower switch could be failing. Check the resister first, it is commonly mounted at the rear of the blower housing under the hood.
Only for the high speed blower function. The lower speeds go thru the blower motor speed resister.
The blower motor speed resister is probably burned out.