Active Vent opens and closes continuously while unit is idle

There is a short in the door interlock or related wiring.

It may need a reset. You can do that by unplugging the power for a minute or two, then plugging it back in and setting the clock.

If it still fails, you may have a failing sensor switch in the vent fan / louver assembly or a damaged component.

There should be a technical sheet hidden behind the grille or behinds the controls. It's very handy to locate and test components.

You can find a video here that shows you how to remove the grille & controller in about 5 minutes.

You can find helpful exploded view diagrams and order parts by entering your full model number here.

My Advantium 240 damper motor was cycling as mentioned above in the morning after a power failure had occurred. Removing the top vent grille and control panel I could see the inlet damper was opening fully and stopping about halfway closed then retrying. Removing power and cycling by hand, i could move it freely until just before it would contact the micro switch at home position where there was a hard stop. I removed the light assembly on top of the cavity and was able to access the rod that spans across to the outlet damper near the halogen light. A combination of fiddling with the connecting rod inside the light housing and manually cycling the inlet damper reseated the rod and everything was working again. My guess is the power failure was the cause and hopefully the issue won't return.

I have this same problem occasionally. Pull the vent grill open and look for a white cam that rotates when the microwave is on. To the right of that cam, there are two gray switches. The bottom switch should have a red tab that pops out. When the vent grill opens and closes continuously, the red tab is stuck in. Take a flat screwdriver or tooth pick and push gently in on the red tab to release it. It must get stuck due to grease or dirt accumulation. Good luck.

Interesting post, because I have the same problem! I have spent the better part of today researching and taking our microwave apart (partially) to inspect the top portion re: outside vent. Everytime the microwave is on, the "active vent door" (manufacturer's term, not mine!) opens. Apparently this is normal. But it also opens when you turn on the vent fan, when cooking on the stovetop. I don't like this feature, because I think it 'overrides' the outside venting system. I double checked our outside vent to ensure that when this oven was installed, the person did in fact allow the flap to be open when the fan is on (he did). So I think what 'our' problem is, is that the microwave active vent sort of interferes with the outside vent, thus more of the cooking smell being blown into the house instead of the outdoors. I was thinking of simply disconnecting the gizmo that make the active vent door open each time you use the oven and/or vent fan option however I don't think that's a good idea as apparently the main purpose of the active vent door is to keep the electronics of the microwave oven from overheating. The more I read about this version of microwave, the less impressed I am with it. Lots of electronic issues with it. I am not fussy either with having the microwave over the cooktop. Sorry I don't have a solution for your problem but I do feel your pain!!!

If the cooling fan, light and turntable run continuously when the door is open, but not when it is closed, your secondary interlock (bottom door switch) is shorted (always on).

Even if it's shorted, the actuator button (usually red) will still move up and down when you open and close the door.

It will need a new door switch.

See the service manual here. See our file on door switches here.

We're happy to help you with free advice and we'd appreciate your thoughtful rating of our answer.

if unit runs with door open then one of the door switch is stuck closed.there are 2 door switches and they could be assesed by removing the control panel.disconnect wires from top and bottom switches and chkf for continuity.they should be normaly open when the door is open and closed when door is closed.one of them will closed even when door is open.replace that bad one.

When the unit begins the never ending opening and closing cycle, turn the vent fan on for a few seconds and then turn the fan off. This seems to stop the active vent from opening and closing. If this is GE quality, this is the last thing that I am going to purchase. GE refrigerators are garbage and now I am having problems with a new microwave oven.

A simple test is to place a piece of bread in the microwave ( it heats up very fast) and then if your microwave was actually ON and generating RF, the bread would get hot very fast.. If it remains cool then only the fan is on. It appears that you may have a faulty door switch thou because once you open the door, your microwave should be off..

Are you sure the VENT is not on? That blower will operate regardless of the door open or closed so you must switch it OFF.

The magnatron is shorting, overloading the high voltage transformer. From the picture this looks like an older unit and is probably not worth a magnatron replacement.