Have you become frustrated by a dryer that just takes too long to dry your clothes, towels, or linens? Is the dryer overheating or maybe not heating at all? There is a component inside the appliance that, if defective, could be responsible for all three of these common dryer problems: the cycling thermostat.
What does a cycling thermostat do?
Both gas and electric dryers use a cycling thermostat to help regulate the air temperature within the appliance. When the dryer is started, voltage will pass through the cycling thermostat as well as a high limit thermostat, and, if applicable to the model, a thermal fuse, before reaching the burner assembly in gas models or the heating element in electric models. The cycling thermostat, usually located on the blower housing, will monitor the heat within the blower housing to ensure the air temperature doesn’t get too hot. During normal operation, the air temperature should be between 120 and 160 degrees Fahrenheit. When that temperature is reached, the cycling thermostat is designed to switch off the voltage to the burner assembly or heating element to prevent the appliance from overheating.
If the cycling thermostat fails to do its job, the dryer may very well overheat, but it could also fail to heat at all (if no voltage is allowed to reach the heating components) or take longer than it should dry its load due to the faulty thermostat causing the heating element or burner assembly to shut off prematurely (the heating components may turn back on again, but the appliance may fail to reach the optimum air temperature to work efficiently).
Testing a cycling thermostat
The cycling thermostat is not the only part that can cause your dryer to run too long, overheat, or not heat at all. Air flow problems, a damaged blower wheel, a blown thermal fuse, a failed high limit thermostat, a malfunctioning moisture sensor, a shorted heating element, or a defective gas valve solenoid could all be responsible. However, you can often use a multimeter to test electrical components to determine if they have failed and the cycling thermostat is no exception.
To properly test a cycling thermostat, you will need an electric griddle or skillet in addition to a multimeter. Now here’s how you can determine if the cycling thermostat is faulty:
- If using an analog multimeter, first rotate the range selection dial to the lowest setting for Ohms of resistance, then calibrate the meter by pinching the metal ends of the red and black probes together while adjusting the needle to read “zero”.
- If you’re using a digital multimeter, you won’t need to calibrate the device, but you will still need to rotate the range selection dial to the lowest setting for Ohms of resistance or “resistance with tone” if your meter has this option (this means the meter will produce a consistent audible high-pitched tone when a positive reading is reached).
- Make sure the cycling thermostat has been removed or isolated from the dryer (for a proper test, you don’t want any portion of the thermostat to be in contact with the appliance).
- You will first want to make sure the cycling thermostat has electrical continuity – a continuous electrical path present in the part – at room temperature. Since the thermostat is designed to “switch off” at a high temperature, it should always be “switched on” or display continuity at lower temperatures. Be aware that some cycling thermostats will have more than two terminals. On these thermostats, the inner terminals are only used to control low heat settings, so you should touch the red probe to one of the outer terminals and the black probe to the other outer terminal to accurately test the part.
- Does the meter read “zero” Ohms of resistance when the probes are in contact with the outer terminals? Then the thermostat has electrical continuity at room temperature. However, if the analog meter’s needle doesn’t move, or the digital meter’s LCD display does not change significantly, the thermostat does not have continuity at room temperature, and you know the part is defective without further testing.
- Since the cycling thermostat is a switch that is actuated by temperature change, you will need to confirm that the electrical continuity is interrupted at a higher temperature. As noted above, cycling thermostats will switch off between 120 and 160 degrees Fahrenheit depending on the thermostat. There should be number printed on the thermostat itself indicating the temperature the component will switch off at when reached. For example, a thermostat with “L155” printed on it will switch off at 155 degrees Fahrenheit.
- To test the thermostat’s response to temperature change, place the component on the electric griddle or skillet and set the heat to an appropriate temperature (for a thermostat with a “L155” designation, set the heat slightly higher than 155 degrees Fahrenheit).
- Hold the two multimeter probes against the outer terminals as the griddle or skillet heats up to the designated temperature. If the cycling thermostat switches off, or displays no electrical continuity, within five percent of that temperature, the part is functioning properly. However, if the thermostat does not switch off, or switches off prematurely, you will have likely identified the culprit behind your dryer malfunctioning.
How can I find the right cycling thermostat for my dryer?
If you’ve determined your dryer’s cycling thermostat is defective, you’ll need to replace it with a new one. But you’ll want to make sure you’re purchasing the exact thermostat that matches your dryer model. This is where Repair Clinic.com can be a big help, taking the guesswork out of identifying the right part. Simply enter the full model number of your gas or electric dryer in the Repair Clinic website search bar, then select “Thermostat” using the “Part Category” filter followed by “Cycling Thermostat” using the “Part Title” filter. The resulting thermostat will be the one that works with your dryer, and it won’t be a knock-off since Repair Clinic stocks genuine manufacturer replacement parts for gas and electric dryers from the biggest names in the industry, including Whirlpool, Electrolux, Kenmore, GE, Maytag, LG, and Samsung.
Since the company went on-line in 1999, Repair Clinic has been dedicated to helping do-it-yourselfers take on their own repairs. This is why you’ll find thousands of instructional videos, diagrams, schematics, and articles on its website to guide you, step-by-step, through repairing gas and electric dryers, along with all other major home appliances, outdoor power equipment, and heating and cooling products. Check out the site’s video library to see if there is a video showing you how to replace the cycling thermostat on your particular dryer model.