The famous “loads-in-series” circuit configuration is one you’ll see used all over appliances. Did you know that the hot surface ignition system in gas ovens is a classic loads-in-series circuit?
Another example is switching in a dropping resistor (via the time contact configuration) to be in series with the timer motor for a particular dryer mode. If you don’t understand what I just said, then you don’t understand these circuits BUT you will after you watch the short video below.
Seeing this loads-in-series configuration is key to understanding how old-skool dryer circuits function in both timed dry and auto dry modes. And why would you want to know that? Well, how can you possibly hope to fix something if you don’t understand how it’s supposed to work? That’s like the baboons in 2001: A Space Odyssey poking and screeching at the mysterious black obelisk.
Before the days of computer control boards in appliances, engineers used other ways to make appliances do what they wanted them to do. Like this old-skool GE dryer.
What’s the difference between timed dry and auto dry and how does this affect my troubleshooting to find the cause of the problem? Could be low heat, timer not advancing in timed dry, whatever.
If you understand how a circuit is supposed to function, you don’t need to memorize “tricks” (if this problem, replace that part), you just read the circuit for your Load of Interest, identify test locations, and git ‘er done. This video is an excerpt from a recent Live Dojo workshop with other techs where we spent an hour going over these circuits. Even though it’s an excerpt, you’ll still the idea. Give it a watch:
As you can see, there’s some interesting Circuit Fu™ going on in this old-skool dryer. The difference between timed dry and auto dry comes down to that one resistor and a particular combination of timer switches, which is conveniently laid out for us in a simple timer chart.
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