Recently I was heating up lunch like I normally do, which is using the microwave. I put my food in, selected the time, waited for the light to turn on and my food to spin around and around, finally coming out hot like magic. Only instead of turning on, nothing happened. Here is how I fixed my microwave for less than $5 by replacing a faulty door switch.
Symptoms of a Bad Door Switch
If you are experiencing any of the below symptoms, there is a good chance you have a bad microwave door switch:
- Your microwave doesn’t start up when you close the door and press the start button
- Your microwave’s interior light, turntable, or fan turns on automatically when you open the door without you hitting the start button
- Your microwave pauses randomly in the middle of cooking as if you had opened the door when the door is still tightly shut
I was lucky because a day before the switch completely failed the microwave would randomly turn off in the middle of heating. When I bumped the door, it started up again so I had an idea it was a bad switch.
If you or you know someone slightly handy, consider opening up the microwave to take a quick look to see if it is a problem with the door interlock switches before you toss your dead microwave into the trash if it has any of the above problems.
A Word of Warning
I discovered the screws holding on the microwave’s cover were Torx security screws. The manufacturer wanted to keep people out because inside the microwave is a high voltage capacitor that could electrocute you even if the microwave is unplugged.
Tip: No Torx security bits? Use a small screwdriver inserted between the pin and the inside of the screw. Twist to break the pin and use a regular Torx bit to finish unscrewing.
To be completely safe, you should discharge the capacitor before you go poking around inside your microwave.
The capacitor is usually located at the bottom right corner of the microwave.
Locating the Door Micro Switches
For most microwaves, there will be not one, not two, but three or even four switches. If one of these switches goes bad, your microwave will stop functioning correctly.
The door switches will be mounted on a bracket behind the front panel near the door latches. They will usually be either black or gray, about an inch long and 5/8 inch tall. You will see wires connected to the terminals on the switch.
For my microwave, there were three switches which are circled in red.
How to Test For a Faulty Microwave Door Switch
The first thing you should do to test the micro switches is by opening and closing the door. You will want to first rule out the possibility the latch or hook is broken and not activating the switch.
Watch to make sure the latch activates the plunger on the top of each switch as you open and close the door. When the door opens and closes, the plunger should depress and pop back up.
For my microwave, I noticed the plunger on one of the switches stayed down when the door was opened and closed. This was the bad switch.
If all the door switches and latches appear to be working correctly visually, the next step is to test that they are working correctly internally.
You will see two or three terminals on the switch. The terminal on the bottom of the switch will usually be the common (COM) and the ones on the side will be a normally closed (NC) or a normally open (NO) terminal.
If you don’t know which terminal is which, there will be a diagram on one side of the switch. Look for which marking the terminal is located next to.
Remove the wires connected to the terminals.
Using a multimeter set for continuity, touch one probe to the COM terminal.
Now if you touch the other probe to the NO terminal, it should read no continuity because that circuit is normally open. Now press down on the plunger. You might sometimes hear a ‘click’ and your multimeter should report there is continuity.
Testing the NC terminal is similar to testing the NO terminal. Keep one probe on the COM terminal and touch the other to the NC terminal. You should have continuity when the plunger is up because the circuit is normally closed. When you depress the plunger, the circuit should open and your multimeter will say there is no continuity.
Replacing the Faulty Micro Switch
Once you have found the bad switch, remove it from the door panel. The switches will usually be mounted on pins through the holes at the corner of the switch with brackets holding it in place.
Once you get the microwave door switch out, you could open it up and try to fix it if you are super cheap, but it will likely fail again soon after. A better long term solution is to replace it since they are so inexpensive. These switches are usually rated up to 100,000 operations electrically and 10,000,000 operations mechanically.
To find a replacement switch, look on your old switch for the voltage rating and the type of switch you need. It might have one terminal that is normally open (NO) or normally closed (NC). It could also have both NO and NC terminals, known as a Single Pole Double Throw or SPDT switch. My microwave had two NO switches and one NC switch.
My switch was rated for 15A – 1/2HP – 125/250 VAC, 0.6A 125 VDC or 0.3A 250 VDC.
You can order a normally open micro switch or a normally closed micro switch on Amazon for about $5 with the above rating. You can also order a SPDT micro switch with both the NO and NC terminals and only use one of the two terminals.
In my case, I ordered a replacement Honeywell brand SPDT switch from Grainger online for about $2 and picked it up at the local warehouse since it was a short drive away.
Here is the new switch installed. I wrapped the unused terminal with electrical tape to keep anything from coming in contact with it.
One thing to watch out for – I’ve seen these switches being sold online for as much as $30 when searching for OEM parts for specific microwave brands. Don’t overpay for a $5 switch when a new microwave can be picked up for $60. These micro switches are very common and are used in everything from icemakers and dishwashers to arcade machines.
Replacing a microwave door switch is a simple process that takes less than half an hour. With a little knowledge and a few dollars, you could save your old microwave from going in the trash.
We have become a throwaway society where we are likely to throw out a malfunctioning appliance than trying to repair it. This leads to our landfills being overflowing with junk, which in turn is harmful to the environment.
Our old microwave has been working day after day for almost a decade. Replacing a basic door micro switch will hopefully result in many more years of heating up pizzas. While a new microwave might cost only $50 to $120, my parents picked up a new microwave from Walmart less than 5 years ago and it has already started rusting on the inside. Newer does not always mean it is made better.