Clothes dryers are probably one of the simplest major appliance to troubleshoot and repair. All electrically heated clothes dryers are alike in structure, as are gas-heated clothes dryers; each model is slightly different. Because of variations in controls and wiring, your most important tool will be a service manual for the dryer that you are working on.
Troubleshooting an Electric Dryer That Doesn't Heat Up
Unplug the dryer from the wall.
Slip the putty knife between the top of the front panel and the top, releasing the clips holding the top in place. Tilt the top back.
Remove the front panel, drum and drive belt.
Referring to your service manual or to the wiring diagram found on the inside of the dryer's case, locate all the critical parts: thermal fuse, thermal cut-out, cycling-thermostat, high-limit thermostat and the heating element terminals.
Set your DMM for the 200-Ohm range; remove one conductor from the thermal fuse and thermal cut-out. Take a continuity reading through them by placing the test probes across them. If either one reads as an open circuit, replace it.
Remove one of the wires from the heating element, take a resistance reading and compare it to the reading indicated on the schematic. Any significant variation here indicates a bad element and you need to replace it.
Troubleshooting a Gas-Heated Clothes Dryer
Unplug and open the dryer as indicated in the steps above.
Check all thermostats, thermal fuses and thermal cut-outs as you did for the electrically heated dryer.
Plug the dryer in, set on the heat cycle, jumper out the door safety switch using one of the alligator test leads and take a voltage reading across the igniter's terminals. The DMM should read line voltage of 120 volts. Another voltage reading here indicates a bad igniter.
Unplug the dryer, remove one wire from the gas solenoid valve coil and take a resistance reading. A good coil will read approximately 150 Ohms. A significantly higher or lower reading indicates a bad coil and you need to replace it.
Check to see if the gas valve is opening. Jumper out the door safety switch, set to a high heat range and plug the dryer in. Shortly after the igniter starts to glow, you should hear a click indicating that the gas valve has opened.
Check the functioning of the flame sensor. Jumper out the door safety switch, set to a high heat range and plug the dryer in. If the igniter continues to glow after 12 to 15 seconds without the valve opening and the gas flowing, you have a bad flame sensor.