I have a 1999 Saab 9-3 that I acquired 2 years ago and the car window motors are breaking one by one–I just had the third one fixed!
When your mechanic replaces the motor, he should be lubricating all the window tracks and the linkage (aka regulator).
So you’ve replaced several motors on one door? When they break, do you still hear the motor whirring or did that stop as well? It is unusual for a motor to burn out under normal use because they are fused. Saab is notorious for having motors fail, though (certainly mine failed as well).
Most of the time, when they break, the gear on the motor will strip so the motor will still turn but it can’t engage the gear on the window’s mechanism.
You may need to grease the mechanical components after a motor is replaced. If there’s too much mechanical resistance, the teeth on the motor tends to strip out.
After you get it fixed again, periodically use a little silicone lubricant* on the window’s rubber seal where it meets the edge of the door frame. When that dries up or gets stiff, it will resist the window’s movement by quite a bit.
*PB blaster, but the silicone lubricant - not the grease as that will make an unholy mess on your window. You won’t see the silicone lubricant. Home Depot sells it.
Perhaps the window frame (or track) is bent or twisted, creating excess resistance. Make sure the window goes up and down smoothly with minimal resistance.
Related to what Goldwing mentioned, it is possible that this 13 year old car suffered accident damage prior to your ownership. If–for instance–there was damage to the doors and they were not repaired properly, it is possible that this situation cannot be resolved short of replacing the doors.
I hope that I am wrong, but I did want to throw this possibility out there for you to consider.
If they’re on different doors, than it’s possible that they’ve reached their lifespan and the forth one will go out soon too.
If they’re on the same door, return to previous replys.