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When you are checking a unit of any kind you should be keeping your eyes open for signs of arcing and melting at all of your wire connections and contact points. We find issues with melting terminals on contactors and in disconnects regularly, but rarely do we think about the relationship between circuit ampacity and wire size and the connections to our equipment.

First, consider the fact that a #10 wire doesn’t always have an ampacity of 30 amps, it has an ampacity of 30 amps with a 60° Celsius rated assembly at 30° Celsius ambient. 


Now, look carefully at the wire and the contactor at the start of the article.

The wire (conductor) is rated at 90° and the contactor is rated at 75° when torqued down to 22 in/lbs on screw type terminals and 40 in/lbs on lug type.

So the entire assembly is only as good as the weakest link and the weakest link is the terminals and the terminals are only as good as the contact they are making.

Conclusion: The termination points are usually the weakest point of the circuit

When sizing conductors don’t forget ALL of the termination points. From the breaker to the disconnect to the unit, every termination point should be properly connected and the rating checked if you intend to use any ampacity other than 60° Celsius. 

Check those terminations.

For more great info on this go HERE

— Bryan

I have spent the last few days checking run capacitors on various systems with several different meters and this is what I found.

#1 – Comparing Start wire amps against Run + Common under the clamp together is meaningless as a practical test.

I used this test on 3 different systems with 3 different meters and came to the same conclusion, whether the capacitor is way too large, way too small or the right size, made no repeatable difference in the reading no matter how we read it.
Even if this is a valid test (which I cannot confirm at this time) the difference is within the uncertainty tolerance of the meter so it’s not useful for field testing.

#2 – The under load test does work (If your meter works)

reading the amps at the herm (compressor start wire) terminal multiplying by 2652 and dividing by the start voltage (herm to c) on the capacitor does work consistently on the compressor and the fan motor however some meters are less accurate at lower amperage readings so that may make a slight difference.
#3 – Power Factor works as a test but it’s a small change
I tested several systems with the Testo 770-3 in power factor mode by installing too large and too small capacitors. The power factor did decrease in all cases when the incorrect size was installed but in some cases the difference was very slight (from 1 to .99 with a 15 mfd too small run capacitor in one case). This means that while it is a valid and useful test it may not be sensitive enough to act as verfication that a capacitor is slightly outside of allowable specs.
— Bryan

This is a quick article from the archives that got a big response 4 months ago. I also just did a Facebook Live video this morning baring my soul on the topic of flowing nitrogen in response to an Email.

Enjoy.

Why is it called single phase 240 when there are two opposing phases?

I wondered why two 120v opposing phases was called “Single phase 240” for years.

Then someone pointed out to me that a typical “single phase” pole transformer only has one power leg entering and two coming out.

This freaked me out. How can a transformer primary be one phase, a SINGLE sine wave and output two perfectly opposing sine phases?

It’s just two separate winding wraps in OPPOSITE directions on the secondary. Stupid simple, but I just never knew it.


So unlike a three phases services that uses all three power phases from the power supply, the single phase service only uses one. The second phase is “created” in the secondary of the distribution transformer itself and is the same “phase” but opposite.

Pretty cool.

— Bryan

This quiz was written by Benoît Mongeau

 

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This article was written by Senior Refrigeration tech Jeremy Smith. Big thanks to Jeremy for his contributions to HVAC School and the tech community. 


Having spent many years in the trade and many years reading posts from techs on forums and social media, a big issue that I see is that troubleshooting is something of a lost art.

Troubleshooting is where the rubber meets the road for a service technician. Nobody cares what certifications you have, what union you belong to or anything else. If you can’t find the problem and solve it in a timely fashion, your customer and employer are not going to be happy.

One of the things that I think most guys struggle with is the mental aspect of troubleshooting. I’ll relate this in the form of a recent call I was sent on to “clean up”. It was a no heat call in a small convenience store. Trane RTU on a zone sensor.

The tech called me and related that the unit had a call for heat at the unit but the ignition sequence didn’t start. We talked a little about the problem, he checked some limits and a few other things. He wound up ordering an Ignition board and limit sensors. These were replaced late that night and the unit still didn’t work.
I was sent the next morning. Now, we get into the mental part of troubleshooting. 

I met the tech so that he could communicate the basics of what he did. We talked for about 10 minutes and he went on to his job and I went to have a chat with the trouble unit.

20 minutes later, I had the problem solved. I found a failed RTRM board. Now, you guys that do Trane all the time probably aren’t surprised, but let’s analyze what went wrong and how this could have been handled on a “one stop” basis.

What did I do that the first Tech didn’t?
For starters, I took everything that I was told about the unit, what it was and wasn’t doing and what everybody and their brother thought was wrong with it and I threw it all out. Put it in a box in my head, closed the lid and locked it.

I dug out the basic Trane “Service Facts” book and started the troubleshooting procedure from Step 1 and followed it to the end.

Now, I can make these arrogant claims about how I’m a Billy Badass service guy and how I’m more awesome than anyone else, but the simple fact is that I’m not. I do things a little differently and think a little differently than many others  and that sets me apart.

What did the first Tech do wrong? While I’m not in his head, I think that he focused on why the heat didn’t work instead of taking the unit AS A WHOLE and diagnose it as a whole. Kind of like the guy who can’t figure out why the fridge is warm and spends an hour working on it only to find the plug pulled.

So, the the mental aspect of troubleshooting cannot be ignored. 
Start at the beginning, work the process and troubleshoot the entire system. Being willing to read the manufacturers troubleshooting info isn’t a newbie move, it shows maturity.

Work on the troubleshooting mindset, don’t be a parts changer.

— Jeremy

(Edited by Bryan Orr, any mistakes are my fault)

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