Dear Tom and Ray:
This problem already almost cost me my fingertips, so you've got to help me. How does a power window know that it's reached the top of its travel and it's time to stop? I have a 2000 Subaru Impreza wagon, and the driver's window motor keeps trying to push the window up even after the window reaches the top of its range. This applied so much torque where the motor is mounted to the door that the bolt holes got distorted and the window didn't fit right anymore. I was able to straighten out the mounting (which involved the window regulator cutting my fingers, as mentioned above), but the same problem will recur when I'm closing the window if I don't let go of the "up" button at exactly the right moment. I can't figure out how the window motor normally should be shut off when the window is fully closed. Can I make my window behave itself again? Thanks for any help.
RAY: Well, we could suggest that you let go of the "up" button when the window is closed, but I'm guessing you want a more elegant solution than that.
TOM: I don't know how all automakers handle this problem, but many of them use a thermal switch in the motor.
RAY: Here's how it works. The motor pushes the window glass up. When the window is closed, the glass obviously can't be pushed anymore, but the motor is still trying to push it.
TOM: So, very quickly, the electric motor -- encountering resistance -- starts to draw more current and generate heat.
RAY: A switch in the motor detects the heat and shuts off the motor. Then it resets itself for the next time.
TOM: I'm sure there are more sophisticated systems out there now. But in a 2000 Subaru, that'd be my guess about the mechanism. And if I'm right, that means you need a new window motor.
RAY: If you want to endanger some more fingertips, you can go to a junk yard and pull a window motor off a "retired" Subaru, and hope it doesn't have the same problem. But if you want to cherish your remaining fingertips, buy a new window motor and consider letting a mechanic endanger his fingertips on your behalf. Good luck.