What causes the inside of microwave to have excessive condensation?

Make sure there is no liquid under the carousel plate inside the microwave, this could be from condensation and may cause the issue.

Also, if you know how you may need to check and make sure it is at full power.

Air from inside the oven is getting by the seals around the inside glass and condensing on the cooler outside glass layer.

A microwave oven works on the principal of a high power high frequency radio transmitter. The device that emits the microwave energy is a tube called a magnetron . When you run the microwave empty with nothing to absorb the microwave energy it is all reflected back to the magnetron causing it to overheat and destroy itself or cause failure in the High Voltage power supply due to excessive current draw.This is caused by standing waves.

Rust can form from the steam and condensation as you say, and it's a good idea to always cover food and wipe the oven out after using it. You can sand off the bad paint and rust the same way you can on a car, and then touch up the paint if it's a minor amount. Spray paint specifically made for microwave cooking cavities is available. (You don't want to use paint that may have metallic components.) It may be available locally if you have appliance parts stores in your area, and you can find the paint online as well. There's no need to replace the oven just yet, unless you find a good deal on a new one and you're looking for an excuse.

That is normally caused by the clear plastic adhesive cover either having been removed or missing. It covers the perforated door inner and stops condensation and food particles from getting inside the door cavity where is cannot be cleaned.

Check the door interlock switches. One faulty switch will cause this problem as will excessive condensation problems.
Hope that helps.

Hello there
you can hear the oven running and it sounds normal but there is no heat then there is an internal problem with the high voltage circuitry or you may have a problem with the circuit board. Changing the circuit board or the high voltage components is something that you want experienced hands to do.

Intermittent heating problems are often caused by steam making condensation of the electronic components or a loose connection in the circuitry. If it is moisture the circuitry will dry out and work after some time. If it is a loose wire then it will need to be fixed by a technician.

If your unit microwave runs but is buzzing very loudly, then you have problems with the magnetron, the high voltage capacitor, or the power diode. These components are all high voltage components and need to be treated with great care. A good technician knows how to diagnose and repair them safely.

If you observe sparking inside the microwave, turn it off immediately. This can be caused by metal inside, or can also be caused by excessive food or liquid buildup. If it causes any burn spots you will need to have then repaired or fix them to have a safe appliance.

This will give you many of the basic causes for problems in a microwave oven. As you can see there is very little that an untrained person can safely do to repair this appliance.
This can however give you some idea of what to expect if you need to call a repair technician to work on your appliance.

It`s not you that`s caused the problem, it`s the condensation from the cooking which gets under the paint, It`s worth investing in a stainless steel lined oven. Ian

Many over-the-range microwave ovens suffer from intermittent problems caused by excessive moisture from the range/stove entering the microwave cabinet and collecting on the circuitry. Often the problem is with one or two simple connections that may need tightening or soldering. But, to repair these components, the microwave cabinet needs to be opened. So we recommend that you seek the assistance of a qualified appliance repair technician.