Let's take a look at the interlock switches in a Kitchenaid microwave-oven combo unit with a simple question to answer: which of the microwave interlock switches should be closed when the door is closed, and which should be open?

Here's the schematic for this model with the switches in question circled:

Should be simple enough to find the answer to our question. In fact, most schematics worth their salt tell you the state the unit is in as shown. Ours has just such a note:

Seems simple enough! But wait... is it referring to the door of the conventional oven portion of this unit, or the door of the microwave oven? It's a little ambiguous. But even if they are referring to the main oven door, surely they would be consistent and also draw the schematic with the microwave door closed as well.

That seems like a reasonable theory, so let's proceed on that assumption and see if we can find any more information in the tech sheet that confirms it.

Here we go -- we've got some specs for the interlock switches in the diagnostics section of the tech sheet:

Huh, interesting -- if we compare the specs for the primary switch to the schematic, they're implying that the microwave door is open...

...and the monitor interlock switch specs agree with this.

But wait...

The secondary interlock specs say that that switch should be open as shown on the schematic when the door is closed. So we have a contradiction in our specs. The schematic must be showing the state of the circuits with the microwave door either open or closed -- there's no in-between. So how do we reconcile this?

Well, for starters, we stop relying on these dummy directions, and we start analyzing the circuits in the schematic functionally. That is to say, we'll trace out our power supplies and figure out the only way that the circuit actually works. This is a key skill for reading schematics: you have to understand circuits, electricity, and the technology being used to make sense of things.

Applying our circuit mojo, we can determine the following:

The circuit as drawn in the schematic can only be with the microwave door open. Seems silly that the microwave door is open and the oven door is closed, but there you have it. With the switches in this state, the microwave control board gets power, but the magnetron doesn't. There's no way that this is the "door closed" state, since the magnetron could never run and you would never get heat in the microwave. Therefore, this must the "door open" state.

And here's what the circuits look like with the door closed:

There we have it: another case of misleading specs conquered by schematic know-how. All in a day's work for an Appliantologist!

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