- Tech Tips
Watts law states that Watts = Volts x Amps. If a particular motor needs to do 1 horsepower of work at 120 Volts it will draw about 6.22 amps. And yes in an inductive load like a motor it’s not quite as simple as VxA=P but we are keeping it simple here.
A motor designed to do the same amount of work (1HP) at 240v will draw half the Amps (3.11).
This does not make the second motor “more efficient” because the power company charges by the Kilowatt NOT by the amp.
) If you take a load that is designed for a particular voltage and you DROP the voltage it will also decrease the wattage according to Watts law (Watts = Volts x Amps) as well as decrease the amperage according to Ohm’s law (so long as the resistance remains the same).
Let’s say you take a 5KW heat strip that is rated as 5Kw at 240v and you instead connect it to 120v.
It would then only produce 1.25 kw and draw 1/4 the amps, this is because while we may call it a “5 Kilowatt heater” it is actually just a fixed resistor designed to do 5 kilowatts per hour of work in the form of heat at 240 Volts. Cut the Volts in half you also cut the amps in half and you decrease the amount of work done down to 1/4 because Watts = Volts x Amps.
Callbacks are horrible… They kill the trade from every possible angle in ways that are hard to fully quantify or make up for. They destroy customer satisfaction, reduce technician morale by causing long hours resulting in unprofitability for companies and less earning opportunity for everyone. Possibly worse of all, callbacks tell customers that you are no better than their cousin the maintenance man or the $35 an hour Craigslist tech. If they wanted to call someone back they could have just called them instead of a true pro.
Callbacks make me furious!
They have always made me furious. Back when I was a tech there was NOTHING I hated more than having a callback… Wait… I take that back, I hated being accused of a callback when it wasn’t a callback in my mind even more.
Since those immature days of pitching a fit whenever I got a callback, I have come up with my definition of what is and isn’t a callback.
Callbacks Are –
What we have learned is that the only way to reliably prevent callbacks is to come up with systems and processes that actively PREVENT callbacks rather than assuming that if you are a good tech they won’t occur. Often we would blame the customer, the follow-up tech or faulty parts for callbacks when it was actually within our power to prevent if we were more proactive. Here is what we learned.
Look Around More Carefully
Before you start diagnosis with tools look over the equipment for anything abnormal. Strange sounds, signs of abnormal condensation and oil spots can all be signs of trouble. Look for wire rub-outs, loose connection and arcing. If it looks like work was done recently, double check that the correct parts were used and that they were installed properly. If wires are a mess, electrical connections exposed, refrigerant lines rubbing out or severe corrosion/deterioration on critical metal parts it should be addressed with the customer.
Never just fix the first problem you find and leave. If that’s all you do you won’t have a low callback rate and you will miss opportunities to serve the customer better. In my experience, the vast majority of systems have either initial installation/commissioning deficiencies maintenance issues, abrasion concerns or just plan faults that get missed when the tech fixes only the first and most obvious problem.
Diagnose More Precisely
The proper and full diagnosis of HVAC/R equipment isn’t that difficult if you are using the proper tools and techniques, but we still hear techs say “it should be fine” when looking at a charge or “That looks pretty normal” when taking an amperage reading. These aren’t things that a good diagnostician guesses at, it is either within design specifications or it is in need of repair, alteration or upgrades and the customer needs to be communicated about it. KNOW the target evaporator DTD, condenser CTOA, motor RLA and system design capacity vs. delivered capacity for the piece of equipment you are working on. If you don’t know what these things mean then start HERE and download the MeasureQuick app to help. Once you stop guessing you will get it right the first time more often and prevent some nasty callbacks.
Improve Your Workmanship
Most bad workmanship is due to poor training, tools, supplies and real or perceived time constraints. You always have time to do the work correctly or you need to FIND time to do it again. None of us get everything right, but you can work to improve your workmanship with every job you do whether it is how you make a wire connection to how to connect ducts or making a flare that never leaks. Get it right the first time and leave it looking like a pro did it instead of a handyman or a kid fresh out of trade school.
Keep the right tools and materials on your truck to execute great workmanship and then do it a little better each time based on what you learn along the way.
If parts are required make sure to get photos of EVERYTHING you can find, data tags, parts tags, boards, compressor model and serial etc… going back to a call just to get a model # because it was missed or written down wrong is a huge waste of time.
Eliminate the Careless Errors
Walk the job before you leave and put your tools away in their proper place. This will help prevent leaving disconnects out, caps off, float switches tripped, thermometers in the duct, screwdriver on the roof etc…
Some of you are just more prone to these sorts of careless mistakes but that is not an excuse, you just need to come up with systems that prevent these forgetful errors. Here are the best ways –
The final test is a gut check. If your gut tells you the diagnosis isn’t right, you didn’t make the repair right or the customer isn’t 100% understanding what’s going on then please DON’T LEAVE.
I know it can be tempting especially after a long day or an especially difficult call or customer but trust me, leaving never makes it better. Hang in there, read up on the system, perform more tests, check the ducts again whatever you need to do but don’t bail.
Sometimes you will have a customer that you just know is going to turn around and call back. You can tell they aren’t listening to you about your findings or they have a misunderstanding about the system operation. These are the ones you want to MAKE SURE you get your recommendations in writing, clearly spelled out with a signature.
If you really want to ensure it doesn’t come back, spend 15 extra minutes and write them a nice, positive email and copy your dispatcher and your service manager with a description of what you found, what you recommended, what you repaired, any system condition issues and how they should expect the system to operate with photos attached. It will really reduce those immediate callbacks from difficult customers.
I am like most contractors and techs, I’ve heard about HEPA for a long time but I never looked into how it could be integrated into a A/C IAQ strategy until now.
First… What HEPA is –
HEPA (High-Efficiency Particle Arrestance) is a, ASME, U.S. DOE standard that specifies a capture rate of 99.97% of particles sized at 0.3 microns.
Becasue the HEPA standard isn’t something is regulated or policed there are many filters and products that use the term in one way or another. Even the term “True HEPA” has no scientific meaning and is often used to market products that don’t meet the DOE standard.
For the sake of simplicity, let’s just stick with the DOE standard and call anything that has been tested to capture 99.7% of 0.3 micron particles HEPA.
Let’s start by answering the question on everyone’s mind at the moment –
HEPA has been demonstrated to effectively capture particles the size of Coronavirus
So much so that in the airborne infection isolation rooms the CDC allows air to be circulated out of the rooms when it has been filtered through a HEPA filter
HEPA filtration is effective on many different particle sizes and had been shown to be even MORE effective when particles get smaller than 0.3 microns due to some weird behaviors of tiny “nano” particles called Brownian Motion.
Don’t believe me? This is a great article on the topic by our friends over at Smart Air Filters
One reason HEPA filters are rated that 0.3 microns is becasue particles of that size are dangerous to human health and are in the size range that have been demonstrated to be the hardest to remove.
The issue with HEPA is that it works best with lower air velocity AND they are SUPER restrictive. This means that running all of the air for your A/C system through HEPA is going to be tough if not impossible. This is why manufacturers have often turned to other technologies like UV, electrostatic, cold plasma and oxidizing ions to “assist” less restrictive filters.
Some of these products may hit the 99.7% number but they may not do as well at filtering the smaller than 0.3 micron particles, they may also generate other byproducts like O3 or Formaldehyde or they may have costly maintenance required. This isn’t to say these other products are always a bad idea but many aren’t as tried and tested as HEPA.
In the photo above we are installing a bypass HEPA filter on the return of a system that serves a dentist office. In this case the blower runs continuously so we are using the HEPA filter to constantly filter 300 CFM of the 1700 CFM system airflow. In this case the HEPA unit comes with a carbon prefilter to help with odors and VOCs and the location has multiple filter back ceiling returns throughout the structure with pretty low face velocity due to the number of them.
We added 20x20x1 MERV8 carbon filters to all of the filter back returns, the bypass HEPA system and MERV 11 filters in the existing 4″ media filter racks.
This did result in a static pressure that was slightly higher than we would like in a perfect world (0.7″wc) but we performed a full MeasureQuick system test and found it was still performing well.
All of this was done at a price point similar to many of the high-cost UV / Ionization / PCO type solutions but without some of the questions marks those can bring, especially in a medical environment where the risks of chemical interactions and viral spread are higher.
Alternative Methods of Install
In an ideal circumstance, the air from the bypass HEPA filter would be pulled from a central location inside the space and then discharged into the return AFTER the equipment filter to effectively reduce system static pressure and prevent the unneeded step of filtering air through the system filter after it has been HEPA filtered.
Like most things, the existing design will often dictate what is practical rather than ideal and one of the beauties of HEPA is how many different ways it can be installed.
Also, running the blower continuously on a low speed will help with filtration but may or may not be a good idea depending on moisture load and equipment dehumidification capacity.
We are now offering HEPA solutions because it has been demonstrated to be effective above the other options, is cost-effective and can be applied in a variety of applications without adding system static when installed in a bypass fashion.
Sure, it doesn’t replace the existing system filter but neither do many of the other options being sold today.
P.S. – As a final word on the topic… I know I will get messages about hundreds of other air purifying tech out there. Before asking more questions please have a look at these resources.
You have seen the C terminal on a dual run capacitor before. You have also seen the C terminal on a compressor.
It stands to reason that they would both connect together right?
They don’t connect together and they aren’t even related, at least not in the way that you think.
In both cases, the C denotes a “common point” in the dual capacitor it is the common point between the fan capacitor (fan) and the compressor capacitor (herm).
In the compressor, it is the common point between the run and start windings (this is why R+C + S+C = R+S if you ohm a compressor)
The C terminal of a dual capacitor is actually fed from the OPPOSITE leg of power as the C terminal on the compressor. This is because you must power the start and run windings with the same leg and common with the other leg.
A way to remember it is memorizing “The same leg that feeds start feeds run” and the C terminal on a capacitor is actually the common feeds for the start winding of the compressor and fan (OPPOSITE side from the fan and herm plates on the capacitor)
So compressor terminals
C goes to one leg of power
R goes to the other
S goes to the HERM terminal on a capacitor with the other side of that capacitor (C) going to the same leg that feeds R.
C what I’m saying? Confusing
With 208v or 240v circuits the L1 and L2 high voltage incoming lines make no difference which is which when you connect. You could swap them on the L1 and L2 on the contactor and it wouldn’t change anything. But once we decide which is connected to Run and which is connected to common on the COMPRESSOR then we need to hook the run side to capacitor C not the compressor common side.
There is also ANOTHER common common we see and that is the secondary side of a low voltage transformer that is opposite from R or hot. You may notice that many low voltage transformers have an ungrounded secondary meaning that either of the wires in the secondary could be hot or common depending on how you hook it up.
In other words… one side of the transformer is designated HOT because we connect it to the line side of our control switches (thermostats, defrost boards, safety circuits) and common is the common point where all the loads connect on the opposite side of the circuit from line.
If you are new to the trade and you see the designation C or the word common don’t assume it is the same as other C and common terminals and start connecting stuff together… Unless you like creating smoke.