Most household appliances generate heat during operation. Some of them are designed and designed for heating (an electric iron, an electric kettle or a boiler for heating water), and for the majority, a strong increase in the temperature of their body and internal filling is an undesirable side effect of their functioning. To prevent overheating, a thermal fuse is installed in series in the power circuit of such devices.
Design and principle of operation
Before you check the thermal fuse for performance, it will not be superfluous to familiarize yourself with its principle of operation and device. After all, this situation often happens: a refrigerator or an iron has stopped working, you have to give it in for repair or buy a new one, and the fault is a small part, the cost of which is cheap. Knowing how and what to check can save you a lot of money.
The principle of operation is based on the property of different metals to expand when heated with different intensity. The bimetallic plate bends under the action of high temperature, which is used in thermostats to open the supply circuit.
Structurally, this protective element consists of two parts:
- electric with normally closed contacts;
- mechanical with a bimetallic plate connected to the contacts of the electrical part.
The electrical part is usually enclosed in heat-resistant plastic, while the mechanical part is usually enclosed in aluminum.
Possible malfunctions
As noted above, the contacts must be normally closed - at a heating temperature not higher than the permissible electric current must flow through the fuse. After the temperature limit is reached, the thermal fuse trips and the contacts open.
The first possible malfunction is open contacts in the normal state. The second malfunction - when the threshold temperature is reached, the contacts do not open or open when heated above the nominal value.
Method of testing for serviceability
There are some tips on how to check the thermal fuse. It all depends on whether you have a multimeter or a regular dialer at hand.
First tip on how to check the thermal fuse with a multimeter in resistance measurement mode:
- transfer the device to the measurement moderesistance;
- attach the probes to the fuse contacts - if the resistance is close to zero, then the contacts are closed;
- heat the metal part of the thermal fuse (with a lighter, soldering iron or dip in hot water) and check the resistance again - it should be infinitely large.
During the cooling process, a slight click may be heard - this is the contacts are closed. If before heating the resistance is zero, and after heating it is infinity, then the part under test is in good condition.
This test method is the most accurate, but there is not always a measuring tool at hand. The following tip on how to check the thermal fuse gives an approximate result:
- heat the part to be checked and listen - there should be a slight click when the heating temperature approaches the nominal;
- should also make a click when cooling down.
If a part is "silent" when its temperature changes above the nominal and below the nominal, then it is most likely faulty.
Expert Tips
There are models of thermal fuses that do not return to their original position after cooling. They have a button on the body to put the contacts in a closed state. Before checking the thermostat, you should make sure that it does not belong to this type. Otherwise, there will be no click and resistance with a value of zero.
And the last advice from experts: before checking the thermal fuse of the refrigerator, boiler,vacuum cleaner or other household appliance, it must be disconnected from the circuit. Otherwise, shunting through other parts may show incorrect results when measuring resistance or continuity.
