Why won't the wipers work on a 1999 Escort after they iced up once?

Check the fuse in that circuit. If they are ok, then check to see if the motor is working. If the motor is working, then the agitator/gearbox is damaged, and need replacement. Get a new motor assembly from a salvage yard. Tim has covered the solution to the problem. As for the answer to the question: When the wiper motor was turned on while the wipers were covered with ice, the fuse probably blew because the motor shaft was locked, resulting in high current.