How to Check the Thermostats and Fuse
The dryer uses multiple thermostats to regulate the temperature. When the temperature is higher than the preset limit of a particular thermostat, the thermostat breaks the circuit and the heater goes off. When the temperature cools enough, the thermostat closes the circuit again and the heat can come on.
Before testing the thermostats or fuse, unplug the clothes dryer or shut off the power at the fuse box or breaker panel to avoid an electrical shock hazard.
Most dryers have a choice of temperature settings, therefore a separate thermostat is used for each setting. The selector switch or timer control then routes the circuit through the appropriate thermostat.
If a thermostat fails, it may prevent the heat from coming on, This happens because the thermostat does not close the circuit when the temperature falls below the operating temperature of the switch. It is a simple matter to test a thermostat; it should show continuity when the switch is cool and no continuity when it is warmer than its rated temperature.
A thermostat can also fail by being always on, no matter what the temperature. This switch would show continuity whether it was hot or cold. In this case, the heater would not shut off and the the dryer could dangerously overheat. As a safety precaution a second thermostat is used, a thermal fuse. The power will be cut to the heating circuit if the maximum safe temperature is exceeded. In most cases, this is a one time fuse. The heater circuit will not function until the fuse has been replaced. Of course, it will be necessary to determine and repair the underlying cause of overheating or the fuse will just cut out again.
The thermostats are usually grouped together. The are typically oval in shape and about an inch and a half in size. They may be on the blower housing, under the lint trap or inside the vent line. There should be two wires connected to each thermostat.
Label the wires and connections so that you can properly reconnect them later. The wires are connected with slip on connectors. Firmly pull the connectors off of the terminals (do not pull on the wire itself). You may need to use a pair of needle-nose pliers to remove the connectors. Inspect the connectors and the terminals for corrosion. If either is corroded they should be cleaned or replaced.
To test the thermostats or fuse, set the multitester to the ohms setting X1. Touch one probe to each terminal. You should get a reading of either zero or infinity. At room temperature, the thermostats should have a reading of zero. When the thermostats are heated to their limit temperature, they should switch off and you should get a reading of infinity. The fuse should be tested at room temperature for continuity.