How Gas Dryer Parts & Components Work Part 2
This page provides a description as well as simple testing methods for each of the components related to a gas dryer. All tests should be preformed with the dryer unplugged and all wires connected to the part being tested unplugged.
(Note: Label all terminals and connecting wires before disconnecting them for proper reinstallation.)
Igniter | Thermal Fuse | Hi-Limit Thermostat | Thermal Cut-Off | Cycling Thermostat | Thermostat Heater | Start Switch | Timer | Motor | Temperature Switch | Valve Solenoids (Coils) | Flame Switch | Burner | Blower | Belt | Belt Switch | Door Switch | Drum Bearing | Belt Pulley | Drum Support | Thermistor | Air Flow | Gas Supply
The dryer's start switch is a momentary contact push switch that allows electricity to energize the motor. Once the motor has begun to spin, an expanding contact within the motor, called a centrifugal switch, expands to maintain contact after the start switch has been released. Some models that have a "finish guard" or "wrinkle prevent" option will automatically start the dryer from time to time after the dry cycle has ended to prevent the clothes within the dryer drum from becoming wrinkled. These start switches have an internal solenoid to activate the switch automatically without it needing to be manually pushed. This style of dryer start switch will have three contacts instead of two.
Remove all connected wires and check for continuity across the two main terminals. While pressing the switch, there should be no resistance measured (a closed circuit, allowing electricity to flow). Three-wire dryer start switches can be checked in the same way. Look at your wire diagram or a chart on the switch for test points. The switch itself can be described in the same way as the above style, but the secondary coil contacts should give some resistance to activate the switch.
The dryer's timer routes electricity to the correct dryer components or system at the proper time. Timers are expensive, rarely fail, and are often misdiagnosed. The timer should be allowing electricity to flow to the dryer's burner or heating element and motor when needed.
Test: Use your dryer's wiring diagram to check for voltage being supplied to the heating circuit or motor circuit.
The dryer motor is used to create the circular motion required to turn the dryer drum and blower. The dryer motor also completes an electrical circuit. Once the motor has begun to spin, an expanding contact within the motor called a centrifugal switch expands to maintain contact after the start switch has been released.
Test: A motor can be checked for resistance across the start windings and main windings. The proper resistance levels and test points can often be found in your dryer's wire diagram. In some cases a large amount of lint can collect on the motor causing it to over-heat. In other cases the contacts to the motor may become loose and not allow electricity to enter or leave the motor circuit. This can cause the motor to not run or other components to not work properly. If you have a "dead" motor you should also check the door switch, belt switch (some models), and timer before replacing the motor.
Temperature Selection Switch:
A clothes dryer's temperature selection switch is a simple switch that will send electrical current to the thermostat heater through resistors. Resistors are usually located on the wires connecting to the switch, but sometimes within the switch itself depending on your model. In this way the amount of current reaching the dryer's thermostat heater is controlled. Some dryer models will use a thermistor and a separate solid-state control board to regulate the dryer's drum temperature. The dryer's temperature selection switch rarely fails.
Test: Disconnect all connecting wires and check for continuity across the switch and all wire harness resistors. If you have a solid-state control board, visually inspect it for burn marks. Use your dryer's wiring diagram for more accurate testing.
Gas dryers use a set of solenoids (also called safety coils) to open the dryer's gas valve automatically after the flame switch has opened, indicating that the igniter is hot enough to ignite released gas. As safety coils are going bad, they will work properly for a short period of time. Then after a half an hour or so of cycling on and off to maintain the drum's temperature, they will breakdown and cease to open the valve. This will result in cool, wet clothing at the end of the cycle. Solenoids commonly need to be replaced in a gas dryer.
Test: If the igniter is getting hot and cycling off after the flame switch opens, but no gas is released, the coils are likely the cause.
The flame switch (also called the window sensor) is used in gas dryers to guarantee that the igniter is hot enough to ignite gas once it is released from the valve. When the flame switch is cool it is closed, allowing electricity to energize the dryer's igniter. But after it heats up, because of its close proximity to the igniter, it opens routing power to the valve solenoids to open the valve and release gas. The flame switch rarely needs replacement.
Test: To test the flame switch, support the switch's terminals with a pair of needle nose pliers while you disconnect the two connecting wires. Check for continuity across the switches terminals. There should be no resistance measured when the dryer is cool (a closed circuit, allowing electricity to flow.) If the igniter heats up but never clicks off, replace this switch.
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Remove all connecting wires and check for resistance across the two terminals of the heater. Some resistance should be detected allowing the heater to perform its work. If an open circuit is detected, the heater needs to be replaced. Also check each of the heater's contacts to the outer containment unit of the heating element. There should be no connection. If the heater tests okay, check the connected thermostats for continuity and your home's power supply for full 240-volt supply.
Gas dryers use a burner to generate the heat required to dry your clothes. These valves are extremely reliable and almost never need replacement. The valve is opened automatically by a set of solenoid coils. In some cases, allowing a propane tank to go dry can cause the valve to fail. However, all other possible causes should be checked before the dryer's valve is replaced. The safety coils are the most common cause of a valve not opening. Note: A valve you intend to use again should not be opened for any reason, because this can cause dangerous gas leaks.