The average load of clothes takes about 60 minutes to dry in both gas and electric dryer models. If you’ve set your dryer’s timer for a full drying cycle and pressed the start button only to find the clothes still damp when you open the dryer door an hour later, the dryer is not running as efficiently as it should. While gas dryer models heat the air to dry the load differently than electric dryer models do, both model types share similar reasons for the appliance taking longer than expected to do its job.
How a gas dryer heats
Gas dryer models use a burner assembly consisting of an igniter, gas valve solenoids, and a burner tube to heat the air that dries the laundry tumbling in the rotating drum. The burner assembly is energized by a standard 120 volts of alternating current when the timer and heat setting are selected on the dryer control panel and the start switch is activated. The voltage passes through a cycling thermostat, a high-limit thermostat, and a thermal fuse, if applicable to the model, on its way to the burner assembly.
The voltage then travels through a flame sensor and an initial gas valve coil before reaching the igniter. The igniter will begin to glow, and when it gets hot enough, the flame sensor will detect the heat and switch off, which diverts the current to other gas valve coils. The coils then activate plungers in the gas valve which allows gas to flow out into the burner housing. Since this happens very quickly, the igniter is still hot enough to ignite the gas into a flame to heat the air being drawn through the dryer drum.
To maintain the proper air temperature during a drying cycle, the heat level in the blower housing is monitored by the cycling thermostat. During normal operation, the air temperature should be between 120 and 160 degrees Fahrenheit. When the air reaches the proper temperature for your dryer, the cycling thermostat will switch off the voltage to the burner assembly.
The key to this system working properly is good air flow. Poor air flow is the one predominant reason a gas dryer will seem to take too long to dry. Why is that? If the air flow is poor, the flame will not be pulled through the burner housing in an adequate manner which can cause the high-limit thermostat to heat up and switch off the voltage to the burner assembly to prevent damage to the appliance. The thermostat will reset after it cools, but the drying cycle may continue to be interrupted if the voltage to the burner assembly is repeatedly shut off by the over-heated thermostat. When the dryer is in auto mode, the appliance will take considerably longer than that 60 minute average to dry the load. If the air flow problem is not corrected, the thermal fuse will often blow, and the dryer will not heat up at all.
Dryers will often have a moisture sensor as well to help detect when the clothing has been thoroughly dried. A malfunctioning moisture sensor, or one coated with fabric softener oil, may shut off the dryer prematurely requiring you to run the appliance longer to actually dry its load. Alternately, if the sensor is unable to detect that the clothing has dried, it may allow the dryer to continue to run longer than it needs to if the auto-mode has been selected.
How an electric dryer heats
Electric dryer models use a heating element to heat the air instead of a burner assembly. The heating element is activated when it receives 240 volts of alternating current through two legs of voltage, each carry 120 volts. The timer, heat selector, and start switch on the dryer control panel allow the first leg of voltage to carry the current to the motor, and through the cycling thermostat, high-limit thermostat, and thermal cut-off fuse on its way to the heating element. The second leg of voltage carries the current through a switch on the motor which closes when the motor is running. The current is then sent to the opposite side of the element. Once both legs of voltage reach the element, the circuit is closed, and the element begins to heat the air.
Just like with gas dryers, the cycling thermostat will monitor the air temperature in the blower housing. When the proper temperature is reached, the thermostat will shut off voltage to the heating element. The high-limit thermostat and thermal cut-off fuse will also monitor the temperature of the element and its housing.
Again, poor air flow can result in the dryer overheating. If this happens, the high-limit thermostat may shut off the first leg of voltage to prevent damage to the dryer. If the air flow problem is not corrected, the thermal cut-off fuse on the heater housing will probably blow and the dryer will not heat. If the dryer has a thermal cut-off fuse located on the blower housing as well, that fuse could blow resulting in the dryer not heating or running at all.
Testing dryer components
The cycling thermostat, high-limit thermostat, and thermal fuse found in both gas and electric dryer models can all potentially be faulty, resulting in the dryer taking too long to dry. Fortunately, all of these parts can be tested to determine if the component is defective, or, in the case of the thermal fuse, that it did its job correctly by “blowing”. How can you tell if a part is defective? Use a multimeter to check that the part has electrical continuity – a continuous electrical path inside the part. If the component lacks electrical continuity, it has failed.
- With a properly calibrated multimeter, rotate the dial to the lowest setting for Ohms of resistance.
- Touch one probe to one of the component’s terminals and the other probe to the second terminal (make sure the component has been removed or isolated from the dryer first).
- If the meter display shows zero Ohms of resistance, the thermostat, fuse, or sensor has continuity and should be functioning fine. If you don’t see any change in the meter display, it’s likely the part has no continuity and will need to be replaced.
On gas dryers, you can also test the igniter and flame sensor for continuity, although be aware that the flame sensor should only be tested for continuity at room temperature for an accurate reading.
For electric dryers, you can also test the heating element for continuity. It’s also a good idea to test the 240 volt electrical outlet the dryer’s power cord is plugged into. Since only the first leg of voltage runs the drive motor, it’s possible that the dryer will still run but not heat if the second leg of voltage has been interrupted. If you suspect the outlet is not providing sufficient voltage, you can test the electrical outlet to determine if the full 240 volts are present.
- Set the multimeter or voltage meter to “Volts AC”
- Insert one probe into the center neutral slot and the second probe into the outlet’s left slot – the meter display should read close to “120 volts”.
- Keeping the first probe in the center neutral slot, insert the second probe into the outlet’s right slot to confirm a reading close to “120 volts”.
At the same time, insert one probe into the left slot and the other probe into the right slot – the reading should be close to “240 volts” although this reading will often vary between 210 and 240 volts.
So how can I ensure good airflow for my dryer?
Remember, that one predominant factor that can cause both gas and electric dryers to run too long is poor air flow. To ensure good air flow, the dryer should be located in an open, well-ventilated area with the rear of the appliance kept several inches from the wall.
Anything else? Yes! Small particles of loose fabric from clothing and linens will form lint which collects in the dryer’s lint filter while the dyer is running. Over time, lint build-up can obstruct the airflow which increases the heat in the appliance and can cause it to repeatedly shut off. Here are three good dryer maintenance habits you should acquire to ensure proper airflow:
- Clean out the lint filter every time you use the dryer.
- At least once a year, detach the venting from the rear of the appliance and use a vent brush to clean out the lint and any other debris.
- Periodically, use a vacuum cleaner to suck out lint and debris from the filter housing.
Keep your dryer working efficiently with parts from Repair Clinic
Whether you need a new thermal fuse, cycling thermostat, high-limit thermostat, heating element, igniter, or moisture sensor to keep your dryer working efficiently, Repair Clinic makes it easy to find the exact part that fits your model, including those manufactured by Whirlpool, Electrolux, Kenmore, GE, Maytag, LG, and Samsung. Simply enter the full model number of the dryer in the Repair Clinic website search bar for a complete list of replacement parts compatible with your appliance. You can then use the “Part Category” filter (“Sensor & Thermistor”) and the “Part Title” filter (“Moisture Sensor”) to identify the specific part you need. In addition to millions of appliance replacement parts, Repair Clinic also has thousands of “how-to” videos, diagrams, and articles to help you do the repair quickly and successfully.