Low Voltage Diagnosis Basics w/ Bill Johnson

HVAC School - For Techs, By Techs

Bryan Orr

Training, Careers, Airconditioning, Self-improvement, Hvac, Business, Education, Refrigeration, Heating, Ac, Apprenticeship

4.8 • 985 Ratings

🗓️ 3 April 2018

⏱️ 37 minutes

🔗️ Recording | iTunes | RSS

🧾️ Download transcript

Summary

In this podcast, Bill Johnson shares his practical tips to make low-voltage electrical diagnosis easier in HVAC work. Bill is one of the original authors of the Refrigeration and Air Conditioning Technology manual.

A common issue that techs have in low-voltage diagnosis is that they overcomplicate the issue. Techs should take the time to trace out the system and see where all the wires lead. The techs can be more effective if they know a system's components and those parts' relationships. During diagnosis, some techs also don't allow themselves to use their hands. Bill recommends using an alligator clip on the system as you "walk your way" through the whole circuit for diagnosis.

"Short" is a commonly used term. A true "short" occurs when the current takes an undesigned path with almost no resistance. Some of the things that we casually call "shorts" are actually open-circuit issues where the current doesn't make it all the way through the circuit. Real "shorts" include shunts on the load and blown fuses. If a fuse blows but everything else in the low-voltage circuit seems to be operating fine, check the amperage at the transformer outlet.

Electronic boards give techs a lot of trouble because they seem complicated. But, in the end, these boards are just switches where a hot wire goes in and a hot wire goes out. (The common wire goes straight through the board.) The board is nothing more than a distributor of voltage, and the best way to work on them is to simplify them. You can simplify electrical boards by figuring out the inputs, outputs, and sequence of operation.

Bill also discusses:

Grounding on one leg
Connecting to ground
"Probing" the hot side
Measuring amperage on a thermostat
"Spark-tricians"
Commercial vs. residential low-voltage electronics
Stripping wires

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Transcript

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0:00.0	You're listening to the HVAC school podcast and this show is made possible by our corporate
0:18.2	partners carrier and Mitsubishi Comfort. When you partner with a manufacturer, you need them to keep up their part of the bargain.
0:28.0	They've got to do what they say they're going to do. The equipment's got to do what it's supposed to do. Distribution has to work. You
0:34.2	got to be able to get parts when you need it. If they make a mistake, they've got to
0:37.4	fess up to it. If there needs to be a change in an order, they've got to act quickly.
0:41.3	And that's been my experience with Mitsubishi
0:43.3	Comfort. I've been a Mitsubishi Diamond Contractor for a good many years. I think it was
0:48.0	2008, 2009 when we first became a Mitsubishi Diamond contractor, and it's been a really good experience.
0:55.8	I'm very thankful to Mitsubishi for all that they've done to help me in my business.
1:00.3	So if you're familiar with the Mitsubishi Diamond Contractor program or even if you're not you might want to go check that out.
1:05.5	Just go to meh H VAC.com forward slash diamond contractor.
1:11.0	Meet ZoomL on the 10 second flame-free refrigerant fitting from Parker.
1:15.8	Reduce labor costs by 60% with no braising, no flame, and no fire spotter.
1:20.8	Discover how Zoomlock can help you be more efficient and productive.
1:24.4	Visit zoomlock.com for more information.
1:27.0	Help me welcome the man who thinks a slang psychrometer makes him look like a cowboy, so he always shouts,
1:38.0	Yee-ha while using it. Brian Orr.
1:42.0	That's actually not true.
1:43.0	Because who uses a sling psychrometer anymore? I mean, I used to use one years ago.
1:48.0	And of course, when I did use one, of course I ran around saying yah. I mean who doesn't do that right?
1:55.2	This is the HVAC school podcast the podcast that's four technicians by technicians that helps you remember some things that you might have forgotten
2:02.2	As well as helps you remember some things that you might have forgotten as well as helps you
	...

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