In looking at the various reasons why a dryer isn’t working right, we will want to look at all the possibilities in order of likelihood (this is a continuation from our first part of the dryer repair troubleshooting article that you can see by following that link).
First, unplug the dryer. Next, remove the back panel of the dryer. The back plate is held in place by a series of quarter inch screws. For more detailed information about opening the dryer, or removing or replacing components, watch the video “Deconstructing the Dryer” available at ApplianceAssistant.com.
Once the panel is off you will see some wiring, a few sensors, and a fuse. The fuse is what we want to test.
The dryer fuse is a small white strip mounted near the center of the dryer with two wires attached. This fuse is designed to burn out when it senses that the dryer has reached an unsafe temperature. So if you find that this is the problem, you again will want to make sure that the ducting is flowing out of the house unobstructed. You will also want to verify that the dryer is cycling properly after you replace the fuse or you may have a bad cycling thermostat. We will look more closely at how the cycling thermostat works in a moment.
The safest way to check this fuse is with a volt meter. These are fairly low cost items starting at around $10.00.
So make sure that the dryer is unplugged and then remove the two wires that are attached to the fuse. Next, set your volt meter to measure the fuses resistance by changing the setting of the meter to the omega symbol. With the wires removed contact the two terminals of the fuse. You should get a reading of zero resistance. The same reading you would get if the two leads were touching each other. This shows that the fuse is allowing power to pass through it and on to the igniter. If the fuse tests open, replace it, and if not, let’s keep looking. Leave the back off. We may need to access those parts later.
Now we’re going to lift the top of the dryer and remove the front.
From inside the dryer we can see the burner valve, the valve coils, the igniter, and the flame switch a little more clearly. Okay, so we’re going to assume this time that the igniter is not glowing and that we’ve tested the fuse in the back of the dryer and the fuse was good. So now let’s test the flame switch and the igniter.
Unplug the connection to the igniter and check the igniter contacts in the same way we did the fuse. This time, depending on the sensitivity setting on your meter, we should measure a small amount of resistance causing the igniter to heat up as electricity passes through it. We should not get an open circuit reading. This would tell us that the igniter is broken and unable to heat up.
If the igniter tests good, plug it back in and disconnect the wires to the flame switch. Test it in the same way we did the fuse and the igniter. This should look the same as the fuse. A closed circuit, meaning zero resistance, meaning power can flow through freely. Any part that tests bad should be replaced.
If all of these components test okay, rinse and repeat, meaning check it again. If all of these components actually are okay, then we’re out of the common 90% of the dryer heating problems and are moving on to advanced troubleshooting.
You will need to find the dryer’s wiring diagram to find where the circuit is having a problem. The wiring diagram is usually located behind the back panel of the control console. This may be a little intimidating, but with a volt meter and some patience, and some basic understanding of how to read wiring diagrams, you will be able to solve almost any problem. Remember, practice makes perfect and this is not a one time thing.
You will be able to use these techniques again and again in other applications, so stick with it.
Let’s look at the wiring diagram. As we can see, the left side of the wiring diagram is the black power supply while the right side is the white neutral power return. The power will always move from black to white like water moving downhill. Any break in that path will stop anything in that chain of components to stop functioning. Your wiring might be slightly different so you’ll want to check your wiring diagram.
By this we can see that the power is supplied to the burner by the red wire attached to the timer. It circulates through the high limit thermostat, the thermal cutoff, and the operating thermostat, as well as the thermal fuse before reaching the burner. The electricity then takes the path of least resistance through the flame sensor instead of the coils located on the valve which offer resistance.
The igniter heats up, opens the flame sensor, which is a bimetal thermostat. At this point electricity is forced to move through the coils, opening the valve, because the flame sensor is open. This will continue until the operating thermostat opens because the dryer has reached full temperature.
If the circuit is broken, blocking electricity from reaching the coils operating the valve and cycling the burner off. The flame sensor cools down and closes again causing the clicking noise. When the cycling thermostat closes again, the igniter will then be energized through the flame sensor and the process begins again. Let’s take a closer look at how the cycling thermostat works.
There are many different dryer models. All will have at least a high heat, and a no heat, or air fluff, option. Many will have other options like low or medium heat level options as well as more dry and less dry settings.
The cycling thermostat is what is called a bimetal thermostat which means it contains two small strips of contact material that flex at a particular temperature to open and close the circuit automatically. Open means no electricity can pass and closed means it can pass freely. If this only happens at one temperature, how can the low and medium temperature settings work?
Well, as we can see in the wiring diagram, models with other temperature options have a thermostat heater. Depending on the setting, more or less voltage is supplied to this heater which is attached to the dryer’s cycling thermostat. Low setting would provide more voltage, creating more heat, and a medium setting, slightly less voltage generating less heat. And high settings would not energize this thermostat heater at all. In this way the thermostat is tricked into thinking that the dryer is hotter than it actually is and opens at a lower drum temperature.
Problems with the system can occur when the temperature selection switch fails to send the proper amount of voltage to the thermostat heater, or the heater itself fails to heat the thermostat. This is very rare, but it can happen. A resistance check across the thermostat heater might shed some light.
If the heater offers infinite resistance, meaning an open circuit, it will need to be replaced. It should provide a small amount of resistance to create the heat required. We can check the entire chain of components responsible for burner operation, except the coils, by unplugging the dryer and measuring resistance from the red timer contact to the neutral plug prong which is the right prong if it’s pointed at you.
For this to work the red timer connection must be disconnected or you may get a false reading through other timer contacts. The door switch must also be closed. If you have that disconnected you can still check from the red timer terminal to the blue connection on the door switch. We can also see that after the black wire leaves the igniter it passes by the motor through the push to start switch. You only hold the switch for a moment.
“So how does the dryer continue to run after I let go?” you might ask? Good question. The symbol to the right of the motor is a centrifugal switch, meaning that when the motor spins, the centrifugal force of that spinning action causes contacts to expand outward breaking contact from the start windings and rerouting power through the main windings.
Continuing connection to the black wire, electricity flows through the closed door switch finally becoming a white neutral connection. It then completes its path back through the wall plug to the neutral connection in your home service panel. For this test, because the motor is not running, you will need to press and hold the “push to start” switch. An infinite reading means a break in this circuit.
There you have it. The magic demystified and made clear. And after you fix your dryer remember to help others with your new found knowledge. I hope this information was helpful.