When your tumble dryer inner drum isn't rotating and only making a soft humming noise, it is possible that it could be the capacitor.
The capacitor has suffered a catastrophic thermal and electrical failure (meltdown).
The dark, bubbled material pushing through the plastic casing is the melted internal polypropylene dielectric film, tar, or electrolyte paste that boiled and ruptured out under immense heat and pressure.
Primary Causes of This Failure
Voltage Spikes or Surges: Exposure to an electrical surge higher than its rated peak AC voltage breaks down the thin internal insulation layers. This creates a direct short circuit inside the capacitor, causing immediate overheating and rupture.
Mechanical or Motor Strain: If the electric motor it connects to is seized, jammed, or under heavy mechanical load, the motor draws excessive current. This forces the capacitor to stay energized far longer or harder than designed, causing it to overheat and fail.
Age and Natural Degradation: Capacitors have a finite operational lifespan. Over time, the internal electrolyte breaks down, its equivalent series resistance (ESR) increases, and the normal heat generated during everyday operation eventually causes it to break down completely.
Defective Centrifugal Switch (Start Capacitors): If this is a start capacitor, it is designed to drop out of the circuit via a centrifugal switch within seconds of the motor starting. If that switch sticks closed, continuous power will rapidly boil and melt the component.
Before installing a replacement capacitor, ensure you turn off all power and inspect the connected motor to verify that its bearings spin freely and that it is not mechanically locked up.
