How to Install Microwave Thermostat 3518905500 in a Kenmore Microwave

Quick answer: Unplug the microwave, remove the outer cabinet, discharge the high-voltage capacitor, find the small disc thermostat screwed to the magnetron or cavity wall, move its two spade wires to the new 3518905500, screw it down flat, reassemble and run a cup of water.

Thermostat 3518905500 is a thermal cutout, a small disc switch that opens the circuit when the magnetron or oven cavity gets hotter than it should. It is a one-purpose safety part: when it trips, the microwave stops heating or goes completely dead, and it stays that way until the part is replaced or, on resettable versions, until it cools. Kenmore lists it for 13 models, including microwave 11183509910, and it also appears on several Magic Chef countertop units such as MCO160UB.

Before you start, read the safety section carefully. The manufacturer states that a service technician should install this part because the high-voltage capacitor inside a microwave can hold a lethal charge even after the plug is pulled. If you are not comfortable discharging a capacitor and verifying it with a meter, hand the job to a technician. The mechanical part of the swap is simple; the danger is in what sits next to it.

See part details and every compatible model: 3518905500

⚠️ Safety First
  • Unplug the microwave and wait several minutes before opening the cabinet. Never work on it while plugged in, even for a quick test.
  • Discharge the high-voltage capacitor by bridging its terminals to chassis ground with an insulated screwdriver, then confirm with a voltmeter that it reads zero. Treat it as charged until you have proven otherwise.
  • Do not bypass or jumper the thermostat to make the oven run. It exists to prevent a fire inside the cabinet.
  • Wear gloves; the cabinet edges and the magnetron cooling fins are sharp.
  • Never run the microwave with the cabinet off or with the door interlock defeated.

Tools and Parts You Need

  • Phillips screwdriver and a Torx or security bit if the cabinet screws need one
  • Insulated screwdriver with a long shank for discharging the capacitor
  • Multimeter with continuity and voltage functions
  • Needle-nose pliers for the spade connectors
  • Flashlight
  • Painter's tape and a marker to label wires

Step-by-Step Installation

  1. Unplug and clear the area Pull the plug, pull the unit out from the wall or, on an over-the-range model, take it down and set it on a padded bench. Give the capacitor a few minutes to bleed.
  2. Remove the outer cabinet Take out the screws along the back and sides, then slide the wrap toward the rear and lift it off. Set the screws aside by location because some are shorter than others.
  3. Discharge the capacitor Locate the large metal can near the transformer. Bridge both terminals together and to the chassis with the insulated screwdriver, hold for a moment, then verify zero volts with the meter.
  4. Find the thermostat The disc thermostat is a small round part with two spade terminals, screwed to the magnetron body or the cavity wall near the exhaust. On some models there is more than one; match the one whose location and lead colors correspond to the old part you were sent.
  5. Label and disconnect the wires Tape a label on each wire, then pull the spade connectors straight off with pliers. Do not twist them or you will loosen the crimps.
  6. Remove the old part Back out the mounting screws and lift the thermostat away. Wipe the mounting surface so the new disc makes flat, full contact with the metal it is supposed to sense.
  7. Mount 3518905500 Set the new thermostat in the same orientation, drive the screws snug without crushing the housing, and push the spade connectors on until they seat firmly. A loose spade is a hot spot.
  8. Check continuity With everything still unplugged, place the meter across the new thermostat terminals. A cold thermostat should read as a closed circuit.
  9. Reassemble and test Slide the cabinet back on, replace every screw, plug in, and heat a cup of water for a minute. It should get hot and the oven should not shut off early.

Fit Checks Before You Call the Job Done

  • The new thermostat reads closed on the meter before power is applied.
  • Both spade connectors grip firmly and cannot be pulled off by hand without effort.
  • The disc sits flat against the magnetron or cavity surface with no gap.
  • No wire is pinched between the cabinet and the chassis.
  • The cooling fan runs when the oven starts and air exits the vents normally.

Common Mistakes to Avoid

Skipping the capacitor discharge This is the step that hurts people. The mechanical work is easy; the electrical hazard is not, and an unproven capacitor should always be treated as live.

Mounting the disc on a dirty or bent surface A thermostat that does not touch the metal reads late and no longer protects the magnetron.

Replacing the thermostat without asking why it tripped A blocked vent, a dead cooling fan, or a stuck relay will cook the new part too. Check that the fan spins and the exhaust path is clear.

Mixing up two similar thermostats Some cabinets hold a magnetron cutout and a cavity cutout. Compare the mounting position and lead routing before ordering and before removing anything.

Troubleshooting After Installation

Microwave is dead after reassembly Verify the spades are on the new thermostat and that no connector was knocked off the door interlock switches while the cabinet was open.

Oven heats briefly then shuts off Check that the cooling fan is running and the rear vents are not blocked. The new thermostat is doing its job if the magnetron is overheating.

New thermostat reads open when cold You have a resettable version that has not reset, or a damaged part. Let it cool fully and recheck; replace it if it stays open.

Care Tips After the Repair

  • Keep the rear and side vents clear of grease and cabinetry so the magnetron can shed heat.
  • Do not run the oven empty; nothing absorbs the energy and the magnetron overheats.
  • Wipe the interior and the mesh over the waveguide cover regularly so heat does not build up behind it.

Compatible Models (Sample)

This part is listed for 13 Kenmore models in our fitment data. Always confirm your exact model number on the appliance's rating plate.

Repair Difficulty and Time

Difficulty: Advanced. Typical time: 45 to 90 minutes.

Frequently Asked Questions

Can I do this myself?

The manufacturer recommends a service technician because of the stored charge in the high-voltage capacitor. If you know how to discharge and verify a capacitor safely, the swap itself is straightforward.

Does the thermostat reset itself?

Some thermal cutouts reset once they cool; others open permanently. If yours reads open after cooling for an hour, it needs replacement.

Why did it trip in the first place?

Usually blocked ventilation, a failed cooling fan, or running the oven empty. Fix the cause or the new 3518905500 will trip as well.

Is the part specific to Kenmore?

It is listed for 13 models, including Kenmore 11183509910 and Magic Chef units like MCO160UQ. Confirm your model number on the rating label.

Final Checklist

  • Microwave unplugged and capacitor discharged and verified
  • Wires labeled before removal
  • Old thermostat mounting surface cleaned
  • New 3518905500 mounted flat and screws snug
  • Spade connectors firmly seated
  • Cabinet reinstalled with all screws
  • Cup-of-water test passed with no early shutdown

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