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What is
a thermostat?
A
thermostat is a
device for regulating the
temperature
of a
system so
that the system's temperature is maintained near a desired
set point
temperature. The name is derived from the Greek words thermos "hot"
and statos "a standing".
What is
a dryer thermostat?
A dryer thermostat is usually oval shaped and about an inch and a half in
length. The thermostat contains a bimetal that opens and closes a pair of
contacts depending on the temperature inside the dryer. The bimetal inside the
thermostat is designed to bend at specific temperatures. When the bimetal
bends, it pushes an actuator. The actuator then pushes on a contact, opening
the electrical circuit and breaking the electrical connection to the related
component. When the thermostat cools, the bimetal returns to its original shape
and the contacts close, allowing the current to flow through the circuit.
Have you ever thought about how hot your dryer gets? Thermostats and thermal
fuses are put in dryers for your safety and if you don't maintain them, you
could be putting yourself, your house, and your family at risk.
Your dryer uses of a combination of heat and airflow to dry your clothes.
The heat generated in your dryer is produced by a heating element controlled by
a series of thermostats. If any of your dryer's thermostats are defective, the
results can be disastrous.
Here's how it works: The dryer is turned on and heat begins to
radiate from the heating element into the dryer's drum. The air in the drum
passes by a thermostat. As the thermostat reaches its maximum temperature, the
bimetal bends, cutting the power to the heating element. The circuit stays open
until the bimetal cools. Because the heating element isn't providing additional
heat, the dryer's temperature gradually falls. The bimetal returns to its
original shape and the electric current flows to start the heating element
again. This process happens many times throughout your dryer's cycle.
There are at least two thermostats in your dryer:
cycling (operating)
thermostat and
hi-limit safety) thermostat. The difference between
these two thermostats is their opening and closing temperatures.
The
cycling thermostat is typically found in the path of the air
leaving the drum. A cycling thermostat is usually found on the fan housing or
just under the lint filter area, on the blower wheel housing or inside the
venting/exhaust system.
Some dryers may have as many as five thermostats - one for each of the
different heat cycles. The temperature setting or cycle selected determines
which thermostat is used to control the heat. If your dryer is malfunctioning
on the low heat setting, the thermostat for that particular setting is probably
defective.
The thermostats for the high and medium temperature selections are not the
problem. However, if the dryer isn't working properly for most of the heat
settings, it's probably a problem with your vent rather than the thermostats.
The
hi-limit thermostat protects your dryer from overheating. This
thermostat is usually found on the heating element, housing, or cage assembly.
If the airflow in the dryer becomes obstructed by a plugged or improperly
installed vent, bad drum seals, or a defective blower, the high-limit
thermostat cuts power to the heating element. This means there are other
problems with your dryer.
In conjunction with thermostats, dryers use thermal fuses as a safety
device. Some dryer models may have two thermal fuses to detect extreme heat. If
the hi-limit thermostat fails to cut power to the heating element and the
element gets too hot, the thermal fuse blows and cuts all power to the dryer.
This could mean that a thermostat is defective or something is wrong with your
venting duct, filters, seals, or blower. You cannot reset thermal fuses so once
they blow they must be replaced. Get the proper replacement fuse for your model
and replace the hi-limit thermostat as well. Never bypass a thermal fuse.
Have a look at your dryer's manual for the locations of its thermostats.
It's unusual for a dryer's thermostat to continue operating at a different
temperature than originally intended and the only way to test for this would be
by checking the temperature of the exhaust. You can do this by placing a pocket
thermometer inside the exhaust vent. This test is done with the dryer running,
so be extremely careful.
Checking continuity is another way to test your thermostat. There's a wire
leading to each of the thermostat's terminals. The wires are connected by metal
slip-on connectors. Label the wires before you remove them so that you're able
to correctly reconnect them later. To remove the wires use needle nose pliers
to pull on the connectors - don't pull on the wires themselves.
Set your multimeter to the RX1 setting. With the thermostat at room
temperature, touch one meter probe to one terminal and touch the other meter
probe to the other terminal. You should receive a reading of zero. If a
thermostat is tested when it's heated to its limit, a reading of infinity
should be produced. You should replace your thermostat if it fails either of
these tests.
The thermostat is attached to the dryer with two screws. Remove both screws
and discard the faulty thermostat. Install a new thermostat, securing it in
place with two screws. Reconnect the two wires, put your dryer back together,
and restore power to the dryer. Run your dryer through a cycle to make sure
it's working properly.
Safety Warning: Before performing any tests or repairs on your dryer
disconnect the power source to eliminate the risk of electric shock. You can do
this by unplugging the dryer, removing the related fuse from the fuse box, or
flipping the appropriate switch on the breaker panel.
For better protection of your family and yourself - maintain your dryer
regularly. But if you can't do it yourself, make sure you contact a qualify service
technician to do it for you. www.victorwod1234.blogspot.com
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