Month: June 2019

 

You’ve probably heard the famous last words “Dude, watch this” before a concussion, burn, shock, broken bones or some other bodily harm. This phrase has become synonymous with young guys doing something dumb to impress their friends.

Technicians have two common phrases that may not lead to bodily harm (although sometimes it might) and they are –

“That’s Good Enough” and “That’s Normal” 

Pulling a vacuum for 30 minutes without a micron gauge and then “That’s good enough”.

Doing a standing pressure test and the pressure keeps dropping JUST A LITTLE and “That’s normal”.

Running a 0 superheat and “I see that all the time” followed by some made up reason about this particular equipment, or load conditions.

I have heard lot’s of made up explanations over the years… some of them out of my own mouth and almost all of them being used as a justification for something being good enough or normal.

 

Don’t misunderstand, normal and good enough are both real concepts, but they need to be backed by deep understanding of the equipment you are working on (have you read the entire installation instructions and / or service manual?) and the readings you are taking (Do you understand what they mean, why you are taking them and how your test instruments / tools work?).

If you can’t follow it up with “It’s normal because…..” or “That’s good enough because….” with a real answer, not a made up reason, then you need to keep working.

This is a journey for all of us, but stop for one second and be honest with yourself. When you get frustrated, short on time or feel in over your head… Do you ever use these phrases? If so, congratulations. You are in an elite group of techs  willing to admit what you don’t know.

Now repeat after me…

“I will no longer make excuses for what I don’t understand, I will stop and work to understand what is actually going on until I have it mastered”

 

— Bryan

 

P.S. – Sorry for the repeat after me thing… It’s a bit too much, but this whole article is nerdy as heck so I figured I would just take it all the way.

Have you ever noticed a blower motor rated for 120V draws about twice the amperage of  the same horsepower motor rated at 240V?

This is because motors are rated in Watts or Horsepower and according to Watts law Watts = Volts x Amps.

In order to keep the Wattage output the same at 120V, it draws twice as much current.

This is different than what happens when you drop the voltage of a motor below its rating.

Here is an experiment I did.

I took a regular 1/6 HP 208 – 230v condenser fan motor and tested it under normal conditions at my office and here is what I got


I then connected the common wire to neutral instead of L1 power which leads to approximately 120v applied and here is what I got.


By dropping the voltage by around 50% the amperage dropped slightly, the wattage went to less than half and the power factor also went in half and the motor slowed way down.

The motor slowing down is due to slip in the motor, meaning that the motor is running significantly slower than the speed it is designed for.

This means that not only is the motor running inefficiently, but it is also going to get hot because as the motor runs slower it has lower inductive reactance (the magnetic resistance in the windings). As the inductive reactance drops the windings have lower resistance and thus get hotter.

Even after all of this, the motor still consumes less than half the watts.

Rubber meets the road is that when a motor is designed for lower voltage it will draw more amperage to do the same work becasue it is designed to hit a wattage (horsepower) target at a designed voltage.

When you apply lower voltage you both decrease the work done as well as the efficiency and life of the motor because more of the energy goes to heat instead of mechanical work as the motor slips more and more. You also see higher power factor as the motor begins to slip resulting in even worse power efficiency.

This is one reason why voltage drop is a such an important thing to consider when sizing conductors and why 208-230V units are slightly derated or n both capacity and efficiency when installed on 208v.

Pay attention to Voltage, it can save a lot of money over time in both power efficiency and motor longevity.

— Bryan

How many times have you looked at the bottom right hand side of an evaporator coil and seen all sorts of rust, even on a fairly new coil?

You may have noticed that many evaporator coils and even some condenser coils will start to corrode where the galvanized steel end plates touch the copper u-bends of the coil. This is a common example of “galvanic corrosion” and it occurs anytime two different (dissimilar) metals come into contact with one another in addition to the presence of an electrolyte such as salt water or condensate water when other particles are present in the water. The reason for this is when electrical contact is made between these metals, ions travel from one metal or “anode” to the receiving metal or “cathode”. When this occurs the anode metal corrodes and the cathode metal is protected from corrosion as the anode metal “gives itself up”.

In fact in the 1980’s, the statue of Liberty was found to have galvanic corrosion on the steel substructure where it connected to the copper skin of the statue, resulting in a major renovation.

The chart above shows that different metals have different galvanic properties and some act more as an anode, giving up to galvanic corrosion more easily and others resist galvanic corrosion and are protected by the other metals.

For example, you may be aware that galvanized steel is more resistant to corrosion than regular steel or cast iron. The “galvanized” part of galvanized steel is just a thin coating of zinc on top of the steel that gives itself up to corrosion, therefore protecting the steel below. This method is more effective than many other protective coatings because even if the coating were scratched or compromised the steel below is protected by the zinc and its sacrificial anode properties.

So let’s think about a common copper tube, aluminum fin, steel framed coil. Where all three of these come together. Where the aluminum touches galvanized steel the galvanized part will go first, then the aluminum, then the steel, then the copper. The galvanized (zinc), aluminum and steel that contact the copper tubing actually act to PROTECT the copper so long as they are in physical contact in the presence of an electrolyte. The only issue is that once that steel rots out the copper may not be held in place as firmly resulting in the occasional abrasion leak.

Now, because of recent studies, we know that most coil leaks are caused by formicary corrosion and copper is more prone to formicary corrosion than aluminum and this is why we are seeing so many units coming with aluminum evaporator coils. Just don’t be fooled into thinking that the rusty mess caused by galvanic corrosion is the cause of your evaporator coil leaks. That rusty steel may actually be protecting the copper more than harming it. There are even some companies that make sacrificial anodes that attach to the suction to help further protect the system from corrosion such as THIS. While many techs use a rusty coil as a system sales technique, you are better off actually performing a proper leak detection instead of assuming that rusty steel means corroded tubing.

— Bryan

 

 

 

 

I got in one of these tiny torches the other day to experiment with brazing aluminum in tight spots and one of the techs walked in and asked “what type of torch is that” to which I answered “It’s oxy/acetylene”, he picked it up and looked at it a bit then asked “Does that get hot enough to braze copper?”

It’s actually a tough question to answer simply

When we say does something get “hot enough” we often mean that the TEMPERATURE is high enough to melt solder or brazing rod, but heat is both an intensity (temperature) and a quantity (BTUs), so while this tiny torch is certainly high enough temperature to melt a rod, it may or may not be enough BTUs to heat up the base metal being joined.

The temperature of the flame is primarily dictated by the fuel or fuels being burned as well as the oxygen mixture. The BTUs depending on the pressure being used and the size/type of the tip.

Most torch manufacturers will list the size of the (copper) pipe that the tip is rated for as well as the proper oxygen and acetylene pressures for the task.

So, heat is both a quantity (BTU) and an intensity (Temperature) and when we say how hot or how cold it really depends on what you mean.  But to answer the question… Yes ,you can braze copper with the tiny torch, so long as it is small tubing.

— Bryan

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