My Whirlpool over the range microwave stopped heating foods. All else seems fine with the unit. I tested the door switches and found that the lower switch was 0 ohms when door open and infinity when door shut - the opposite of the upper switch, which was 0 ohms when door shut, as I expected. Does that mean the lower switch is bad? Can a switch "change polarity" like that? Also, can I test to see if the problem is the lower switch by hooking it all back up such that the lower switch doesn't get pressed in when the door it shut, thus making both switches at 0 ohm resistance when door is shut?

I tested using the only 2 terminals on the switch - COM and NO - and when the switch was depressed (door closed), the resistance was infinity. When it was not depressed and the door was open, the resistance was 0. I suspect that is opposite from what should happen?

The microwave is working just fine except it does not heat foods. It does not make any irregular sounds. Lights, clock and control panel work.

I completely removed the switches to test them. Both terminals were disconnected from any wires when I tested. For the lower switch that I think is the problem, I am sure the terminal is the NO terminal. There is no terminal at the NC label - only one at the NO label. I do know that the switches acted differently, for sure. One had continuity when switch was depressed, and the other (the lower switch) had continuity when the switch was not depressed. I have the lower switch with me now (at work). I am not 100 percent what was the terminal on the upper switch - NO or NC - but I imagine it was NO.

I am not good with electrical stuff. I do not feel very comfortable testing much other than the switches, or replacing something that obviously looks broken. The microwave is only 3 yrs old and cost me about $330. If its not a switch issue, I'll probably buy a whole new microwave.

Can't I test to see if the lower switch was the problem simply by bypassing it and connecting the 2 wires together? Or by connecting the wires to the switch and keeping it unmounted so there is continuity at that switch even when the door is shut? I can't hurt anything doing that, as long as the door is shut, can I? If both switches allow continuity with the door shut, and I heat water, I would think all I need to do is replace the lower switch.

Thanks. I intend to try the test.

The problem I now have though, is in the diagram. From the diagram, I cannot tell which switch in the diagram is my lower switch. If I look at the individual part pics, it would seem part 18 is the one most like my lower switch, but in the big diagram, it has 2 terminals coming out one end, unlike my switch which has one terminal on top, and one on the end. Part 8 looks like the upper door switch and I did not see another switch while working on it, although there is a part 7 switch which has 3 terminals in the individual pic - not like either of my 2 door switches. Is there a way to tell which switch is upper and which is lower in the diagram? My lower switch has 2 terminals, one at COM and one at NO, coming out the side farther from the actuator, while the label NC is closer to the actuator but has no terminal.

I know my 2 door switches are slightly different in appearance. It appears one may have a terminal at NC and the other at NO, which would mean they SHOULD act differently, which is what my two switches do. Let me ask this, when the door is shut, should the switches BOTH have continuity (0 ohms) - or is it possible one should have continuity and the other no continuity?

I do appreciate your help, and I don't want to be a pain, but I have more to add. I found a manual from Sears that discussed a Kenmore model that is very similar to mine. On page 24, it has detailed info on the 3 switches, and discussed the NO terminals on part SZM-V16-FC-63, and says the switches should be at 0 ohms when actuator is depressed (door closed).
http://www.appliancefactorypart...ontent/pdfs/130524-8.pdf

Unless they used FC-63 in an unusual (incorrect) way in my microwave, it seems it should be 0 ohm but they are not. I guess I will try my test and see what happens.