Test the following parts.
There are many reasons your microwave won’t turn on, one of which might be a faulty door switch. The door switch, also known as an interlock switch, signals other microwave components to begin powering when the door is closed, and to stop when the door opens. For this reason, everything else may appear in working order but the microwave will not begin heating.
How to test a microwave door switch with a multimeter:
- As you will be testing electrical components, verify that you have unplugged your microwave before beginning.
- Locate and remove the door switch. You will need to remove the cabinet in order to access it. You should also inspect the door hooks that trigger the door switch to verify they are activating the switch mechanically
- To test the switch for continuity, set your multimeter to Rx1, depress the actuator button and touch the terminals with the probes. You should receive a reading of 0, indicating that there is continuity.
- If your switch does not have continuity between the terminals, you will need a replacement door switch.
If your microwave won’t start and the display is blank and unresponsive, the issue may be with the ceramic fuse. This part protects other microwave components from power fluctuations, and causes a complete loss of power when it fails, meaning your microwave won’t work. If you are aware of the cause of the fuse failure, such as opening or closing the microwave door, you can also test the door switch to see if that is working. If you are unaware of the reason for the fuse failure, you may want to test other microwave parts such as the magnetron, high voltage diode, capacitor, and transformer.
How to test a microwave ceramic fuse with a multimeter:
- Unplug your microwave before starting this test.
- The ceramic fuse will be found near the power cord. Remove the microwave’s cabinet, locate the fuse, and remove it in order to test it for continuity.
- Set your multimeter to Rx1 and touch the probes to the fuse’s terminals. This test should produce a reading of 0, showing that there is continuity between the terminals.
- If your test produces a different reading, you will need a replacement ceramic fuse.
Thermal Fuse or Cut Out
A problem with the thermal fuse or cut out could be the reason your microwave won’t turn on. The thermal cut-outs, also known as thermal fuses, help keep the oven from overheating. When the thermal cut-outs fail, your microwave won’t turn on as a safety precaution to keep it from getting too hot. Take this opportunity to also check that the cooling fan is working and not causing the microwave to overheat by cutting off airflow.
How to test a microwave thermal fuse with a multimeter:
- Disconnect your appliance from the power source before attempting this inspection.
- Locate and remove the thermal fuse. You will need to remove the appliance’s cabinet in order to access it and will need to disconnect the wires attached to the fuse in order to remove it.
- With the fuse removed from the appliance, set your multimeter to the Rx1 setting, and touch the probes to the terminals to test for continuity. A properly functioning thermal fuse should produce a reading of 0.
- If the results of your test differ from the above, you will need a replacement thermal fuse.
Door Latch Assembly
Your microwave may not start because of an issue with the door latch assembly. Most door latch assemblies are made of plastic hooks that stick out of the door and engage the door switch when the door is closed, signaling the rest of the controls to power the microwave.
How to inspect a microwave door latch assembly:
- As with most microwave inspections, begin by unplugging your appliance.
- The door latch assembly will be found attached to the door; you will need to remove the inner door panel in order to access it. To inspect it closely, remove it from the appliance.
- Looking for any signs of wear, discoloration, damage, or cracking, visually inspect the door latch assembly.
- If you find any issues while inspecting it, you will need a replacement door latch assembly.
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