How Does an Electric Dryer Work — Appliance Repair Tips
Not all dryers look the same but all of them operate in the same manner through a combination of three main factors airflow, heat, and drum rotation. We will address how these three factors work together as well as potential problems you may encounter.
When operating, the dryer uses a blower wheel to draw air in from the front or rear of the appliance. The air is heated and circulates through the clothes as the drum rotates. The hotter the air, the more effective it is at removing moisture from the clothes. You can expect an average load of clothes to take about 60 minutes to dry. For electric dryers, the air is heated by a heating element and airflow is vital to its proper operation. To ensure your dryer has sufficient air to operate it should be located in an open, well ventilated area, and not in a cramped closet or laundry room. For proper airflow the rear of the appliance should be kept several inches away from the wall. If the airflow is poor, the heat from the element will not be pulled through the heater housing properly. This can cause the high limit thermostat to heat up and switch off the voltage to the heating element. The thermostat will reset after it cools and the process will repeat. However the dryer will take too long to dry because the heat is continually being shut off and the thermostat itself can become damaged. Some models may have a thermal fuse on the blower housing and a thermal cutoff fuse on the heater housing. Either of these fuses can fail due to poor airflow. If this happens the dryer will not heat or it may not run at all until the fuse has been replaced. If functioning properly, the heated air is pulled evenly through the tumbling clothes, and then through a lint screen. To maintain proper airflow it’s important to clean the lint screen after each load.
The last stage of airflow is the exhaust stage. The heated air that has removed the moisture from the clothes must be vented to the outside of the home. An exhaust vent is used for this purpose. There are two types of venting material that can be used. Each has a different length limit. The best type to use is rigid venting which is usually efficient up to 40 feet in length. However, be aware that any bend in the venting impedes airflow and reduces the length limit for efficient operation. For example, each 90 degree bend subtracts 8 feet from that 40 foot limit. The other type of venting you can use is semi rigid. This type of material is usually efficient up to 20 feet in length. Again, any bend will impede airflow. A 90 degree bend will subtract 8 feet from the allowable 20 foot total. Use only rigid or semi rigid venting. The flex vent tubing must be secured with stainless steel duct clamps 4 inched in diameter. There are several brands of clamps such as Vilsun, Lokman, Ideal, and Tech Team https://techteamproducts.com/. We chose Tech Team’s because it has a butterfly toggle that makes it easy to use https://www.amazon.com/Band-Style-Key-Style-Stainless-Collection Clothes/dp/B079RSJCJN/ref=sr_1_7?ie=UTF8&qid=1546285381&sr=87&keywords=dryer+vent+clamp. Any other material may increase the risk of fire as the lint in the vent could ignite during normal operation. Since an exhaust vent clogged with lint is the most common cause of restricted airflow, we recommend cleaning out the vent at least once a year.
As we mentioned earlier, the air inside the dryer is heated by the heating element. This element is activated when it receives 240 volts of alternating current through two legs of voltage, each carrying 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 cutoff 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 heating element. Once both legs of voltage reach the heating element, the circuit is closed, and the element begins to heat the air. To maintain the proper air temperature, the heat in the blower housing is monitored by the cycling thermostat. During normal operation the air temperature is usually 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 heating element. The high limit thermostat and thermal cutoff fuse also monitor the temperature of the element and its housing. Again, if there is an airflow problem, the high limit thermostat may switch off the first leg of voltage to prevent damage to the dryer. Eventually if the airflow problem is not corrected the thermal cutoff fuse on the heater housing may fail, and the dryer will not heat, or the thermal fuse on the blower housing may fail, and the dryer will not run or heat. The heating components that most commonly fail are the thermal fuse, the thermal cutoff fuse, the high limit thermostat, and the heating element itself. If the dryer does not heat or heats inadequately, all of these components can and should be tested individually to determine if one of them has stopped functioning.
Keep in mind that only the first leg of voltage runs the drive motor. Therefore if the second leg of voltage is lost due to a blow in house fuse or a tripped breaker, the dryer may still run even though the air is no longer being heated. If you suspect your electrical outlet is not providing sufficient voltage you can test the outlet using a voltage meter set to volts AC. Be aware that readings can vary between 210 and 240 volts.
As the blower wheel draws the air into the dryer and the heating element heats it the drum is rotated by a drive belt. The belt goes around the entire drum and is looped down to a dry pulley on the motor, which drives the belt, and around an idler pulley, which puts tension on the belt. The drum has baffles inside to lift and rotate the close, which is an important step in the process, as it allows the heated air to dry the clothes evenly. The drum is supported by glides or rollers in the front, and rollers or a bearing in the rear depending on the model. Over time the drum supports will wear out and the dryer may become noisy during use. If the drum is overloaded, or if a support roller, glide, bearing, or pulley fails, the belt may begin to slip. It can also fray and eventually break. When the belt breaks you may hear the motor running but the drum will not rotate. On some models a broken belt will activate a switch that prevents the motor from running. Airflow, heat, and drum rotation are all necessary for efficient dryer operation, and as you can see, all three are interrelated.