Print
Microwave - Normal Operational Characteristics for a Microwave

It is normal to experience any of the following with a microwave oven:
  • Steam or vapor escaping from around the door.
    This does not mean that the unit is leaking microwave energy. The door is designed to allow heat and steam to escape to prevent the overheating of the unit. It is normal to see some condensation between the door panels, unless the condensation does not dissipate within a reasonable amount of time.

  • Light reflection around door or outer case.
    The light is located outside the oven cavity and can reflect light out around the hinge, door, outer case, and oven lamp access cover.


  • Dull thumping sound or hum while cooking at power levels other than high.
    When using a power level other than HIGH or 10 the magnetron tube cycles on and off to obtain the lower power. This cycling of the magnetron tube causes this dull thumping, pulsating, or humming noise. When combination cooking in microwave/convection models, the cycling of the convection element and fan will alternate continuously with the hum of the magnetron and the fan.

  • Humming noise when the microwave is not in operation.
    The transformer emits a slight humming sound that is usually not noticed. The transformer is used to power the clock.


  • The interior fan will run continuously while the microwave is in operation to constantly circulate the air to cool the working parts.

  • Exterior fan noise on JVM models.
    The fan will make noise similar to a vent hood.

    Note: This fan is controlled by a high/low/off switch but will automatically come on if the cooktop surface transfers significant heat to the microwave. The fan will not go off until the microwave thermostat reaches a lower temperature.

  • Fan bearing noise.
    This will occur if the microwave is operated in temperatures below 50 degrees Fahrenheit. It is recommended that the room temperature be at least 50 degrees Fahrenheit for proper operation.

  • Flickering light under low voltage conditions.

  • The light does not come on when the door is open.
    This is normal on some countertop models.

  • Warm outer case on the control panel side.
    The heat is normal and comes from the power transformer.

  • On models JMT19 and JMT20 ('85 microwave toaster ovens), when in "micro-bake" the lights will dim and the fan will slow down. When it changes to regular "bake" the lights will brighten and the fan will speed up again. This is normal.


  • It is normal for the door to have a little give in it, either up or down or in or out, up 1/8". This will not cause microwave leakage.


  • The Active Vent/Hidden Vent found on the JVM1800 series models will open during operation, and remain open as long as the microwave is running to keep the electronics cool during operation. It is also normal to hear a clicking noise as the "vent" opens and closes.


  • A "clicking noise" upon startup is normal operation. This is found in models JVM1840, JVM1850, JVM1851, JVM1860, JVM1861.