Buddha, All the thermostats and thermal fuses, should produce a "closed" circuit when tested at room temperature with a multi meter set at the RX1 scale on the meter. Cycling thermostats are usually rated at approximately 155 degrees and Hi Limit thermostats at approximately 200 degrees(the temp.range can be found on the thermostat or the label).

If the hi limit switch is "forced to operate as the cycling thermostat, due to an air flow issue, it can and usually does weaken or fail before the cycling thermostat, after all it is a "safety" device, and not really designed for "continuous service" like a cycling thermostat. You may want to disconnect the exhaust vent from the back of the dryer and check and clean the vent system all the way out to the vent hood. A measuring cup with water heated to the temperature rating of the thermostat is a good way to test the thermostat. If all checks OK, suspect a weak set coils on the gas valve.

Buddha, If you've checked and cleaned the vent system and vent hood. The thermostats check proper at room temperature. Remove the front bulkhead and check and clean any lint accumulated in the outlet duct, below the lint filter. Check and make sure there are no clogs or lint built up inside the blower housing, and replace the hi limit thermostat.

Part number: AP4036956