Sam Brown

[Sam Brown]

Ok, no big deal. It just confused me a little on the question since there appears to be two right answers depending where I look.

That question is making a distinction between the pressure after the meter regulator (which we gave as 7″ WC) and the pressure after the appliance’s own regulator (which we gave as 3-5″ WC). The video that you’re referencing is talking about a meter regulator, which is why we have that note mentioning that the pressure would be 5-7″ WC.

Since the question is asking specifically about the pressure after the appliance’s regulator, 3-5″ WC would be the only correct answer.

[Sam Brown]

The exact pressures will vary a bit from manufacturer to manufacturer. What we gave in the unit was some general specs. The important takeaway for you is just that natural gas is used at lower pressures than LP.

[Sam Brown]

In the video on evaporator fans in Unit 1.8 the first video mentions that the fan has a DC power supply which confuses me. Can you clarify please?

Small-scale BLDC motors, like the kind you find used as evaporator fans, are built to run on a 12 VDC power supply. These small BLDC fans do still have an inverter board on them — it’s just built into the fan itself. That little built-in inverter board takes its power supply and inverts it into electronically commutated AC to run the motor, just like a larger scale inverter does.

If any part of that still isn’t clear, let me know.

[Sam Brown]

We’ve got a lot of stuff on diodes that should help you understand them. Here’s a recording of a webinar we gave about diodes over at Appliantology:

Also at Appliantology, I’ve put out a blog post explaining diodes in detail. Click here to check it out.

[Sam Brown]

Good catch! I’ve clarified my previous reply.

The point does stand, however. Due to friction, you do lose some pressure between the evaporator and the compressor inlet, so using that pressure to calculate saturation temperature will still be only an approximation.

[Sam Brown]

1) If another component in the stove ends up grounding to the chassis, would that cause the flame detection system to think there is no flame and keep sparking?

Depends what component we’re talking about. Is it a load or conductor with line on it? If so, you would get a short, and that would cause a lot more problems than just with the reignition module.

2) Also, is the spark voltage always ac?

In modern reignition systems, yes. It needs to be AC for flame rectification to work. Older reignition systems used high-voltage DC, however.

[Sam Brown]

Without a good evaporator thermistor, it’s going to be tough. You can approximate with either a gauge at the compressor inlet or an IR gun, but neither would be very accurate.

[Sam Brown]

By the time the refrigerant has reached the compressor, it will have lost some pressure due to friction and gained some superheat. To calculate the saturation temperature accurately, you would want to use the pressure at the inlet to the evaporator, since you know that the refrigerant will be at saturation there and the pressure and temperature will correspond exactly.

[Sam Brown]

I do see how the wording could be confusing, but that question isn’t saying that PR1 and DLB are EEPs — it’s saying that those are the two test points you would put your meter leads on. When we say that they’re EEPs, we’re referring to the fact that each one is an EEP for measuring across that element. In other words, rather than having to disassemble the unit and put your leads directly on either side of the element, you can simply use PR1 and DLB to do your test. PR1 is an EEP for one side of the element, and DLB is an EEP for the other.

Make sense?

[Sam Brown]

The fact that he was able to measure 120 VAC across the push to start switch means that the door switch is closed. If it were not closed, there would be no valid neutral at the push to start switch to use as a reference for the 120 volts.

Make sense?

[Sam Brown]

Correct! Once that switch is closed, P29-1 and P27-1 are EEPs. But if it’s open, they are not EEPs. So a continuity measurement — or, better yet, a voltage measurement — will tell you if that switch is closed.

[Sam Brown]

The key part of deriving pressure from temperature is that you do your temperature measurement at saturation. At saturation, you can always tell pressure from saturation (and vice versa). That’s why, in the first video of this unit, the Samurai makes a special point of saying that you need a thermistor at the evaporator inlet for approximate low side pressure, and you need to take your temp measurement in the middle of the condenser coil on the high side.

There will be slight variations in pressure throughout one side of the sealed system, but they’ll be relatively small — small enough that we can pretty accurately approximate

I would recommend rewatching the first video in this unit — it covers this in detail. And let me know if you still have questions.

[Sam Brown]

I know exactly which part of that lid switch is tripping you up — there’s that weird connector that seems to bypass one of the lid switches. You’re correct that, if that were a path through which current could flow, it would cause a short. But actually, this is a case of a poorly drawn schematic.

Here’s another drawing of that same lid switch, but you’ll notice a key difference.

Now they just have a dot instead of a line between those two lines — and now the circuit makes much more sense! No shorts here. As for what they’re trying to show with that dot, I’m not sure. They certainly don’t give us any help in that department on the tech sheet (no label or anything). My guess is that it’s perhaps an odd way of representing a fuse.

[Sam Brown]

It really doesn’t matter what the exact number of your meter’s input impedance is on its non-LoZ settings. 7.8 megaohms is going to be just fine — that’s effectively open as far as the circuit is concerned.

The important part is just that you don’t use LoZ when measuring sensor voltage, since that’s voltage that’s not supposed to be running a load.

[Sam Brown]

This question is specifically asking about the board’s power supply, so J1-4 is the correct answer for that.

As for the connection to J2-6, I believe that you’re correct — that would seem to be a sensing line so that the board can tell what state the switch is in. Good spot!

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