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Use EEPs to Troubleshoot This Circuit Entirely from the Control Board

Son of Samurai

Entry posted by Son of Samurai in Tech Talk

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I covered troubleshooting 240 VAC heater circuits in a previous post, but I wanted to revisit that topic with a more specific focus: can you troubleshoot an inop electric heater entirely from the control board?

Why is this useful to look into? Because in real-world troubleshooting, avoiding unnecessary disassembly is key to quick troubleshooting and avoiding liability. This makes finding Electrically Equivalent Points (EEPs) for your electrical test points eminently practical.

Let's look at the circuit in question and get our bearings.

Screenshot_2026-02-14_at_8_16_46 AM-15.png

Circled is the electric heater we're interested in. It's a dual element, so we actually have two parallel heating elements. That's a good thing for our plan to troubleshoot entirely from the control board -- it helps us do that!

Let's look at the heater's circuit.

Screenshot_2026-02-14_at_8_16_46 AM-3.png

Our heater needs both L1 and L2, like all 240 loads. These two legs of the power supply pass through a few controls, which we need to take note of:

Screenshot_2026-02-14_at_8_16_46 AM-16.png

In the L1 side, there are two thermal switches -- the inlet safety and the outlet control backup. In the L2 side, there's the centrifugal switch.

A quick note on the centrifugal switch: notice that there are two electrically separate switches circled, both of which are centrifugal switches. One is in the motor windings' circuit, and it's normally closed. The other is in the heater circuit, and it's normally open. Both of these switches are actuated when the motor starts spinning. We're only interested today in the normally open centrifugal switch in the heater circuit.

Great, we know how our heater gets its power supply, and what controls that power supply has to get through to reach the heater. But what about starting by testing the heater itself? Can we do that from the board?

We sure can, and it's thanks to the fact that we have a dual heater. If we read from one of the heater relays on the board to the other (while the machine isn't running, of course), then we'll read through both heater coils, like so:

Screenshot_2026-02-14_at_8_16_46 AM-12.png

Even if we don't know the exact resistance spec for the heater, as long as we don't read a very high or infinite resistance, we can say with reasonable confidence that the heater is okay.

Now what about all these different controls in the heater's circuit? We can test those from the control board, too!

Let's test those two thermally controlled switches in L1. All we have to do is check from one of the heater relays (doesn't matter which; we just pick one) relative to Neutral.

image.png

This test is done without the unit running. If we have 120 VAC on our loading meter, then we know we have L1 at the relay, and that means both of those controls are good. Simple, elegant, and requires minimal disassembly!

So that's L1 sorted. What about the L2 side of things?

For this one, we first disconnect the heater connection from one of the heater relays (again, we just pick a relay). Then, we start a cycle and check from that wire we disconnected to Neutral.

Screenshot_2026-02-14_at_8_16_46 AM-10.png

With the dryer running, the centrifugal switch in the heater circuit will close. And with the wire disconnected from the relay, there's no current flowing through the outer coil. This means that L2 will be present right up to the wire we disconnected. So if the centrifugal switch is good, we'll read 120 VAC on our loading meter, since we're reading L2 to Neutral.

And just like that, you can check the heater itself and every switch in its circuit right at the control board. How much testing you can do this way depends a little on the exact machine you're working on. This one had circuits that are particularly amenable to troubleshooting with EEPs, but you can almost always find at least some clever tests at more easily accessible points, no matter what you're working on. The key is to look at the schematic beforehand and analyze your load of interest and its circuit, just like we did. Practice that, and soon the EEPs will start jumping off the page at you.

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6 Comments

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Andrew Thompson

Andrew Thompson

Posted (edited)

Love these explanations. Question regarding the final test (checking L2). If I disconnect the outer coil as indicated in the final diagram and measure 120v, why is that not measuring L1 “traveling” through the inner coil and backwards through the outer coil? There won’t be any amperage of course, with the outer coil circuit being open, but wouldn’t you still read the voltage potential present from L1 via the second relay?

Edited by Andrew Thompson
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Son of Samurai

Son of Samurai

Posted

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1 hour ago, Andrew Thompson said:

Love these explanations. Question regarding the final test (checking L2). If I disconnect the outer coil as indicated in the final diagram and measure 120v, why is that not measuring L1 “traveling” through the inner coil and backwards through the outer coil? There won’t be any amperage of course, with the outer coil circuit being open, but wouldn’t you still read the voltage potential present from L1 via the second relay?

Great question!

The reason you don't read L1 at the outer coil relay is because it's being dropped across the inner coil. That's why I drew the red L1 line stopping at the inner coil in that markup. The inner coil has a complete circuit, since we didn't disconnect its relay, so there's current flowing through it and therefore L1 is being dropped across it. But since we disconnected the relay to the outer coil, it doesn't have a complete circuit, so we can read L2 feeding up to our disconnected wire.

Make sense?

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Samurai Appliance Repair Man

Samurai Appliance Repair Man

Posted

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Great example showing why techs need to understand the distinction between voltage potential difference and voltage drop.

Voltage potential difference makes the power supply for a circuit. Nothing else happens without that.

Voltage drop, on the other hand, only appears as electrons are being forced through a load by voltage potential difference and is determined by the Ohms Law equation E=I X R. If current is zero, voltage drop will be zero. 

JohnC

JohnC

Posted

In the last step, what would taking an amp reading on each element tell you? I know that we would need to know the resistance of the outer & inner coil to make sure we get the correct amp reading. The amp readings could be taken while the dryer is in operation on T-14 & N-14 without disconnecting any wires.

Would this be a good test or would it be better to follow the course of action you laid out? I've had an element that was touching ground show an amp reading that was close to what it should have been.

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Son of Samurai

Son of Samurai

Posted

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1 hour ago, JohnC said:

In the last step, what would taking an amp reading on each element tell you? I know that we would need to know the resistance of the outer & inner coil to make sure we get the correct amp reading. The amp readings could be taken while the dryer is in operation on T-14 & N-14 without disconnecting any wires.

Would this be a good test or would it be better to follow the course of action you laid out? I've had an element that was touching ground show an amp reading that was close to what it should have been.

You don’t need to know the resistance to interpret an amp measurement. Amps are a proxy for watts, so you would want to know the watts.

However, since we’re dealing with a no heat issue here, we know just from the symptoms that there aren’t any amps. If there were current going through the elements, they would produce heat.

Where your test would be useful is if you have a low heat complaint. In that case, you might suspect that one of the coils has gone open, but not the other. Your amp test on the two different coils would tell you which is passing current and which isn’t.

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JohnC

JohnC

Posted

Thanks

 

"can you troubleshoot an inop electric heater entirely from the control board?"

I had missed the part about it being a no heat issue.

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