# Month: September 2018

## Parallel Circuit Resistance

In a Series circuit (loads connected in a row end to end) it’s easy to calculate total circuit resistance because you simply add up all the resistances and you have the total.

In a Parallel circuit the voltage is the same across all the loads, the amperage is simply added up but the resistance is a bit more tricky.

It gets tricky to imagine because the total circuit resistance of parallel loads goes down the more loads you add.

For example, if you have one light bulb connected to a power source, the total resistance of the circuit is just the resistance of the bulb.

Add in another bulb in PARALLEL and the resistance of the circuit goes DOWN

When you are calculating the total resistance of a parallel circuit you take each individual resistance and divide it into (not by) one. You then add up all the resistances that were divided into one and divide that sum into one. The formula looks like this for the diagram at the top of the article.

1÷Rt (total resistance)= 1÷R1 + 1÷R2 + 1÷R3

For this particular application as shown above it would be.

1÷Rt(total resistance)=1÷120 + 1÷45 + 1÷360

So 1 ÷ 120 = .0083 + 1 ÷ 45 = .022 + 1 ÷ 360 = .0028

Then we add them all up

.0083 + .022 + .0028 = .0331

Then to find the total you divide one by the total

1 ÷ .0331 = 30.21 Ohms total

As you will notice, 30.21 Ohms is less than the lowest resistance in the circuit. This makes sense when you think about ohms law.

The lower the resistance the higher the amps. Adding in additional parallel loads INCREASES the amperage in a circuit, and we see this ever day when we notice that compressor amps and condenser fan amps added together equals total condenser amps.

So it stands to reason if lower resistance equals higher amps and adding in more parallel loads increases the amps, then adding in more parallel loads reduces the resistance.

Another myth this busts is the idea that electricity ONLY takes the path of least resistance. Electricity actually takes all paths between positive and negative charges and every additional path (parallel circuit) just decreases the resistance between the two points of potential difference. This increases the total circuit amperage, which is why when you try to run two hair dryers on one 15a circuit the breaker trips. Two hair dryers in parallel = lower  total circuit resistance = higher amps.

Not that I would use two hair dryers….. maybe that’s why I’m almost bald.

— Bryan

## How to Measure System BTU output w/ Testo 605i

HVAC school shows how to use the Testo Smart Probes app and Testo 605i’s from the new expanded Testo Smart Probes case. We use the kit to calculate total system BTU removal during operation. Featuring Bryan Orr.

–Bryan

## How to Measure Air Filter Static Pressure Drop

HVAC school measures static pressure drop across an air filter using the Testo 510i from the new expanded Testo Smart Probes Case. Featuring Bryan Orr.

–Bryan

## How to Calculate HVAC System BTU capacity

HVAC school shows how to calculate system capacity using enthalpy. We use the UEI hub kit and some simple calculations to do this. Featuring Bryan Orr.

–Bryan

## Short #22 – Mineral & POE Oil (Podcast)

Bryan talks about the difference between Mineral and POE Oil, the advantages and disadvantages of using them, and when to use them.

If you have an iPhone subscribe to the podcast HERE and if you have an Android phone subscribe HERE.

## Putting Water Inside our Leak Detector

Warning! Sucking water into your leak detector is something you should never do! In the case that this does happen, we see how to get it out with the NAVAC NRP8DI Vacuum Pump.

–Bryan

## Don’t Forget the Service Wrench

One of my most popular YouTube videos goes over how to adjust TXV superheat. It’s a very simple little video that I did at my desk and the other day I got this comment –

“Good Video but I hate to say this BUT, with the title SCHOOL, why would you show the public an instructional video depicting the use of an adjustable wrench on a valve stem? Service valves, valve stems on TXV’s and Acetylene tanks should NEVER be touched with anything but a service wrench… Its hard to unlearn bad habits”

It was a well-deserved rebuke, in my haste I used an adjustable wrench to show the adjustment of the TXV stem rather than a service wrench.

The refrigeration service is as much a staple of the HVAC/R industry as a gauge manifold. It’s really just a square drive ratcheting box wrench, usually with several sized built in with 1/4″, 3/16″, 5/16″ and 3/8″ being the most common

There are many purposes for the refrigeration wrench including –

• Opening and closing acetylene tanks
• Opening & Closing multiposition service valves to the backseat, front seat or neutral seat
• Opening typical residential HVAC Service valves using a 3/16 (liquid line) &  5/16 (suction line) combo hex key (Like shown below)
• Adjusting other square refrigeration valve stems

The primary lesson is that whenever you are making an adjustment on a device, tank etc… you want to use a tool that will do the least amount of harm by damaging the stem edges as well as use a tool that will apply the correct amount of force without providing enough torque to break anything.

A refrigeration wrench fits the bill in many applications and in general getting away from adjustable wrenches is a good idea anyway.

— Bryan

## How to Measure Total Static Pressure w/ Testo 510i

HVAC school measures total A/C external air static pressure demonstrates using the Testo 510i manometer from the new expanded Testo Smart Probes case. Featuring Bryan Orr.

–Bryan

## A Critical Technician Trait in Decline

Our technician Sam sauntered into my office this afternoon like techs often do on a slow Spring afternoon before the Summer hits.

It’s been a long day for me, lot’s of training prep, a bunch of little fires and errands to stomp out and I still didn’t get my article for the day written. I look up at Sam and say “You can write my article today” to which he smirks and says –

“Sure thing, my article will be on perseverance

Now, let’s pause quickly and take a peek inside our business (Kalos Services). There is a lot of sarcasm around here, A LOT!

We know one another well on account of the fact that many of us are related one way or another. Many of us have been friends or acquaintances long before we ever worked together. I knew Sam when I was a punk kid and he was just a baby, riding around the country with his parents and many siblings in a converted school bus turned into a hippy / evangelical Christian family house on wheels.

Fast forward a few decades and his sister married my brother.

Fast forward almost another decade and Sam is one of our techs…. and a darn good one.

Sam is like my brother Nathan and my brothers-in-law Bert and Dan (Who also work here) in that they don’t shy away from making fun of me (or one another) to my face or behind my back. When Sam said that today’s article should be on perseverance I thought he was ripping me… Turns out he was serious.

He scooted his chair in a bit closer and gave me some sincere examples of times newer techs (and even more experienced techs) gave up too quickly rather than seeing a problem through.

Sam isn’t the sort of tech to read more than he absolutely needs to. He’s not a tech or science nerd like me, but he does get the job done and he learns what he needs when he needs to learn it more often than not. We talked a bit more about old-fashioned grit and how it seems to be in decline.

He walked out of my office and I got to thinking… He’s right, perseverance is an important trait that’s in decline among techs and it’s worth taking a few minutes to think about it.

Technology as a Crutch

Techs who never look anything up or read drive me crazy, I’ve been pretty outspoken about that. But I’ve noticed a recent trend towards techs using their phone to “search” for quick answers in groups, on forums and using text to other techs rather than RESEARCHING from quality sources like manufacturer data and quality articles from reputable trade magazines.

It was Dan Holohan who first introduced me to this idea of search vs. research and I think it’s spot on. For complicated problems, you often need to dig a little deeper and read a bit more completely to get to the root of the problem you are facing rather than getting a quick answer.

Common Cases

Sam brought up cases where a blower wheel, fan blade or pulley get “stuck” and a tech reaches for a puller or a grinder way too quickly. Now don’t get me wrong, some jobs require a puller, but some sand cloth and penetrating lubricant along with some “working” of the blade, wheel or pulley can do the job better and just as fast with a bit of patience and perseverance.

Finding a low voltage short circuit is another case for perseverance. So many techs just start swapping conductors rather than systematically working through the circuits one at a time until you find the cause.

Proper electronic leak detection takes time and patience to go through every part of the system before proclaiming that the leak is “in the evap” or even worse that you “can’t find it”. Most good, modern leak detectors have a sensitivity down to 0.15 oz per year…. when that system is dropping a few pounds per month you can… and you will find the leak if you exhibit some perseverance.

Lifting heavy things without hurting yourself requires a lot of prep, thought and perseverance in many cases. Jeremy Smith did an entire series on lifting safely and in some cases doing things that appear impossible to a tech with a bit less gumption.

Do You Have It?

Do you give up after a while? Do you call other people multiple times in a day because you keep getting “stuck”? Do you roll a lot of calls to tomorrow so that someone else can have a look? Have a lot of leaks you “just can’t find” or electrical problems you just can’t seem to solve? Do you feel overwhelmed when things start going wrong?

Chances are you need to more research and less search and dig a bit deeper, look for some grit, gumption, sticktoitiveness, chutzpah, guts, nerve, snap, spark and good old get er done with a dash of “by golly, I can whip this thing!’

There is no manual for this… no quick tip I can give for how to keep a stiff upper lip…. you just need to do it, and you will be glad you did.

Sam and I believe in you

— Bryan

## Detecting Surface Moisture w/ Testo Smart Probes

HVAC school detects surface moisture using tools from the new expanded Testo Smart Probes Case. We show how you can use the Testo Smart Probes to detect surface dewpoint and prevent moisture issues before they start. Featuring Bryan Orr.

–Bryan

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