Chosen Solution
The cheap switch is only part of the problem. Microwave ovens are meant to be shutoff before opening the door. This is not a problem on smaller ovens as the smaller amperage discharge across the switch when you open the door does not harm it. There are two interlock switches one for each leg of the transformer that powers the magnetron, one switch completes the circuit to send power to the relay which then sends power to one leg of the transformer, the other door interlock switch is directly connected to the other leg of the transformer. This is the switch that goes bad when you open the door with the unit on. Transformers work by magnetic charge, when you open the interlock switch the voltage in the transformer will jump the switch eventually destroying it. The relay on the other leg of the transformer can handle the on/off amperage. Go with a better switch. The manufacturer could put in a heavier switch as they use the same switch for small and large ovens but it is unintentional planned obsolescence. The third interlock switch is called the monitor switch and it shorts the power to the transformer blowing the fuse if the other interlock switch gets its contacts locked together or is bypassed.
Hi @templedf , If the plastic is melting then it means that too much current is flowing through the switch and it is getting hot. So the problem is most likely the other component(s) that the switch is connected to. If the switch has the correct power rating then it won’t get hot if the other components are OK, The switch voltage and current ratings should be marked on it Depending on which switch it is it may be the magnetron circuit, the fan circuit or the motor circuit etc. You would need to have the schematic of the oven or at least to trace the wires from the switch (one side would most probably come from the input power connection) and check where it goes to and then check the components if the switch is rated correctly. Be safety aware when working in microwave ovens as they are dangerous if you don’t know what you’re doing. The HV capacitor can seriously injure you as it can store enough voltage (>6000V DC) for months, even if the oven has been disconnected for this amount of time. It needs to be discharged correctly before attempting any repair work. Most simply short out the terminals on the HV capacitor to dissipate the voltage but this can damage the capacitor or if an inappropriately sized screwdriver was used can actually weld it onto the terminals. Most people doing it this way are too impatient to do it correctly. Make a lead (12 gauge wire) with alligator clips at each end and a 10W 1 MegOhm resistor in series i.e. clip- lead - resistor - lead - clip, and connect it between the +ve terminal of the capacitor and the chassis and let it discharge the capacitor. Wait for about 5 minutes and then use the screwdriver to dissipate any residual charge that may be still there just to make doubly sure.
You do not need to replace “bad” switches, just open the switch box with a razor, sand away rusted metals, bend the spring to make stronger. It will work again
What happened on my microwave was that after a while, the switch alignment was a little off between the three door switches, which caused them to actuate at slightly different times when I opened the door. This was totally fine if the microwave wasn’t running. But if I opened the door while the microwave was running, what was supposed to happen was all the switches would get tripped simultaneously causing the microwave to stop; what would actually happen is they would trip at slightly different times, which would cause an overload in one of the switches, cause the switch to fuse together like you’re experiencing, and cause the breaker to trip. I’m not an electrician and don’t know how to technically explain it, but all I know is as long as I press the stop button before opening the door, the switches stay fine and the breaker doesn’t get tripped. I hope this is helpful.
Try buying the actual OEM part. I would get from a local Appliance parts dealer. In Seattle I use Apex Appliance on Aurora., Inspect it at the store and see if it looks materially different? If the wire you say is melting is larger, that could be your issue. I also wonder if the microwave itself could be cooking the switch? It’s an odd theory, but a switch doesn’t usually have high voltage, its usually just a gate for the rest of the circuit; If SOMEHOW the microwave was leaking radiation onto the switch, that could be an explanation too. wrapping the wire in foil tape might help this. Just crazy thoughts, I know.
No, My issue was with the top switch. I was replacing the switch about every 2-3 weeks. I finally gave up and replaced it with an oven from Sharp.
From what I’ve seen there are two major manufactures of Microwave ovens, Look at any brand, you will find a door lock switch that goes straight out with a hole in it, and another type of swich that is like a hook that slides into an opening on the frame of the oven. My KitchenAid has the first type of switch, Whirlpool, Maytag, GE, Frigidaire all have an identical door lock switchs so that is one manufacturer, this is a very common problem! The ones that have the hook type switch (LG, Samsung, Toshiba, Zline) seem to be more reliable in my experience. My Kitchen Aid is bad now and this is the fourth time its gone bad so my extended warranty is giving me a refund of the entire purchase price under their “No Lemon policy”! I’ve had the oven for almost 5 years.
If you have a problem with the microwave blowing fuses or the breaker while opening the door, chances are really good it’s the monitor switch. Which is the middle or second switch. If you remove the plastic “latch board,” the receptacle the door hooks latch into which holds the switches, be certain to reinstall correctly. Because there’s a small plastic hook or clip that must go through the metal structure before the board is slid downward into position. It’s possible to install this without properly seating it, without sliding it downward into position, but if you do the switches will not align properly with the door hooks and it’ll just blow the fuse or breaker again. Also when ordering the monitor switch make sure you order the right one. Because the upper switch has the same KW3 number on it but they’re not the same switch. And they cannot be substituted because the upper is normally open and the monitor switch is normally closed. Lastly, do not open the microwave door while it’s running. Because it arcs the monitor switch internally every time and shortens its life. Let it finish running, or hit cancel. Finally, the price of the switch imo makes no diff. Some are overpriced simply because the supplier is price gouging.
I have another problem with our GE over the stove microwave. The monitor switch is blowing the 20A fuse when I close the door. I replaced the monitor switch twice to no avail. When I disconnect the monitor switch, the microwave works fine. I cannot see a way to misaligned the switch assembly, but it seems obvious that the monitor switch is not opening before the primary and secondary switches close; thus bowing the fuse every time. Has anyone encountered this problem and how can I test this and rectify the problem? Operating the microwave without the monitor switch is probably not the best solution.
These switches are notoriously hard to align properly. If you can get a new bracket to replace the worn one it may help. After ten years you will notice allot of wear on the bracket where the door latches make contact. Mine kept blowing the 20 amp breaker and burning it the center switch. I got tired of trying to fix so I ended up buying a new microwave.
