Some of the sears models had the defrost timer as part of the ice maker, when the ice maker quit so did the defrost system. Look behind the kick plate at bottom , in back remove cardboard and look next to condenser fan ,compressor area. Timer is about 3 in by 4 in with heavy wires red, yellow, blue, black. Look inside freezer for a plastic plug about the size of a dime and two screws about 3 in apart, that is how the timer is mounted two screws diagonal. The thermostat you checked will show open at 60 degrees and must be freezing or cold when you check it with the meter. Don't forget to look at the ice maker if you have one it has gears and the timer under the cover.
