Brand: Kitchen-Aid
Model Number: KCMS2055SSS-1
Main Symptom: Light turns on when starting but doesn’t rotate/heat food
What happens & when: Food was cooking and all the sudden the rotation stopped working and the food was no longer getting cooked.
Error Code (if any): NA
Parts or tests already tried: Turn table motor, magnetron, capacitor
Photos / video link: NA
A few points that strengthen your analysis:
If the cavity light comes on during a cook cycle, that confirms:
Line voltage is getting through at least part of the door switch circuit.
The controller is receiving enough information to initiate a cook command.
The control board is energizing at least some loads through its relays.
Since the turntable motor, capacitor, and magnetron have reportedly already been replaced, it makes sense to focus on components common to the high-voltage circuit rather than continuing to suspect those parts.
The primary interlock switch is a reasonable suspect because it sits in series with the power path feeding the high-voltage system. A switch can appear to function mechanically while still having high resistance, intermittent contacts, or a contact set that doesn’t fully close under load.
A couple of cautions:
Don’t completely rule out the control board yet.
Even if the lamp relay is operating, the relay that supplies power to the high-voltage transformer/inverter may be a separate relay. Some boards can run the light, fan, and turntable normally while failing to send power to the cooking circuit.
Verify what the fan and turntable are doing.
If the light, fan, and turntable all run during a cook cycle but there is no heat, the diagnosis becomes even more focused on the HV power path.
If only the light operates, that changes the analysis significantly.
Door switch failures are extremely common.
Given the symptoms and the parts already replaced, I’d agree that the primary interlock switch (and its mounting bracket) deserves close inspection. I’ve seen loose switch mounts cause a switch to test good with the door open but fail when the door is actually latched.
To test the door switch, unplug the microwave and remove at least one wire from the switch being tested. Using a multimeter set to continuity or the lowest resistance scale, check the COM and NO terminals. With the door open, the switch should read OL (open). When the door latch actuator is pressed, it should read close to 0 ohms. If the reading is intermittent, shows significant resistance, or does not change states cleanly, replace the switch.
I would also closely inspect the door switch mounting bracket. A loose, cracked, or warped switch holder can prevent the switch from being fully actuated even when the door appears to close normally. Try moving the switch by hand while observing the mount for any play. Any looseness in the bracket can cause intermittent no-heat conditions and should be corrected before replacing additional parts.