In our new series Bryan uses some resources from RSES NATE Prep to do some quick videos full of useful HVAC tips and data. In the first instalment Bryan discusses Motor Types.
Visit RSES website here: https://www.rses.org/
In our new series Bryan uses some resources from RSES NATE Prep to do some quick videos full of useful HVAC tips and data. In the first instalment Bryan discusses Motor Types.
Visit RSES website here: https://www.rses.org/
Many installers and service technicians know how to read and use a manufacturer fan table, but this is a quick review with a few extra tips for newer techs. It’s also a good reminder to senior technicians how this easy-to-use practice can also be easily abused.
At installation, it is imperative to the performance and longevity of the appliance to set up airflow properly. A practical way to do this is utilizing the manufacturer-supplied fan tables found in every installation manual. Here’s a review on how to set up airflow on a new system:
For servicing, techs may use the fan table method as a quick and dirty way of verifying airflow without extensive and time-consuming testing. This can be acceptable, but only if the following conditions are met:
Static pressure readings stand alone as a valuable measurement during a service call, and TESP can inform a technician whether more extensive testing is required. But if the equipment has never been worked on by you, or your company did not install the equipment, the fan tables will not be useful until a full-system commissioning has been completed.
Carrier FB4CNF Installation Manual
Another important tip is to always keep the return static pressure below 0.4” w.c. According to many manufacturers’ literature, a return static pressure of 0.4’ w.c. or higher can potentially result in water from the primary drain pan being picked up and thrown around inside the cabinet area, and sometimes into the ductwork.
It is important to understand static pressure measurement is NOT a measurement of airflow. This is where many technicians abuse this method. Static pressure is just that: a measurement of pressure in reference to the space outside the ductwork. Based on lab testing conditions, a manufacturer is able to determine the airflow of a system under a known resistance. Static pressure is used as a proxy to estimate airflow, but this method is only as good as the conditions in which it is applied. Static pressure readings are air density dependent, so zeroing a manometer in a cold, dry attic, then inserting the probes into a humidified, warm duct system will adversely affect the accuracy of your measurements. This method is also heavily dependent on how detailed the manufacturer fan table is. An example of a good fan table would be one that lists the equipment model, if the unit was tested under wet or dry conditions, if heat strips were installed during testing, and any corresponding wattage/rpm determinations under given conditions.
Carrier FB4CNF Installation Manual
The difficulty with using Fan Tables as a way to measure airflow is realizing the resistance across the equipment is dynamic, and will likely change many times over the course of a test (the coil may get wetter as it is loaded with latent heat, the coil will become dirty over time, etc.) Measuring actual airflow is difficult to do, but static pressure measurements are still very valuable, and are a good way to determine if a problem exists and on which side of the ductwork it exists (supply or return).
A great product for measuring airflow in the field is the TrueFlow Grid by The Energy Conservatory. For more information on Airflow and Airflow Measurements, TruTechTools has an entire section of literature and webinars on the topic. Here is a video we recorded for them in 2017 regarding Static Pressure and Fan Tables:
Business isn’t easy. Generally, when I look back at how much work it has taken to get a business off the ground, I wonder if I had known what I know now if I would still be willing to put in all that work all over again.
I’m not sure if transforming a business is easier than starting one, but it’s a painful process and getting started can be daunting. Lucky for you, this blog post came along at just the right time and will help organize your mind around all the soul-crushing work you have to do.
Attract Better People
Are you looking for the same sorts of people in all the same spots your competitors are? Analyze the way you are searching for help. Are you using language and incentives that make it clear to the top 1% in your field that you are the best place to work in your industry?
Do you hire only for experience? or do you hire for mindset and core attributes and train for skill?
Clarify your message
What do you offer and what truly sets you apart from your competition? Don’t give generic answers; if the answers you give to these questions is the same as ANY of your competitors, then it’s back to the drawing board.
Once you have it clear make sure all of your employees can recite it backward in their sleep while underwater in a bathtub (no not literally).
Train your employees regularly
How often do you train your employees? If the answer isn’t on the tip of your tongue then you don’t have a good answer. Anything less than once a week isn’t enough. Habits are about repetition. An emailed memo will not change the behavior and habits of your team. Get out there and train, do role-playing and do it all over again next week.
I confess that the very BEST training in our business happens when we hop in the truck and ride around with our people, often we as leaders are the ones getting the training.
Track your key numbers
First, you need to know your key numbers. For years, baseball scouts thought that RBI and defensive stats were among the best indicators of baseball success. Turns out they were wrong. Billy Beane, GM of the Oakland A’s found that on-base percentage was the most valuable number, so he began choosing players and training to that metric instead of the others. Guess what? They started winning.
For HVAC we find that callback rate, customer satisfaction or net promoter score and billable per hour are some of the best field metrics.
For the overall business, you need to always be clear on your cash and you net value (cash + receivables – payables) as well as keeping a close eye on net profit and overhead %.
Prepare for a rainy day
Take all of your business expenses for 3 months and add them up. Do you have that much liquid cash in the bank? If not, start saving retained earnings until you hit that level of reserves. You never know what tomorrow holds and the businesses that last have enough cash to weather a storm.
Learn from your customers
Start by taking customer surveys, but not the way big companies do it. Instead, create a list of 2-5 questions and call your best customers once a year and check in on how they feel you are doing. Some great questions are:
Get better at sales
Sales is both overrated and underrated, simultaneously. Overrated because what most people think of as “selling” is an antique remnant of the cigar-smoking, back-slapping, used car salesman model. Sales aren’t pressuring customers to buy stuff by a few dudes with the “gift of gab”.
Sales is something all employees need to be doing with every customer by discovering their needs, fears, and desires and then providing them with solutions for which they pay you. Sales is both elegantly simple and ridiculously difficult as it requires the lost art of listening.
The good news is that once you accomplish these 7 hideously daunting tasks you will have a business you can truly write home about…. If you still have the energy.
Newer technicians often get hung up and frustrated when searching for low voltage shorts. This is understandable due to the broad spectrum of possibilities for the location of the short. However, this doesn’t mean the process needs to be complex. The time it takes to find a low voltage short may vary greatly depending on where the short is located, what components are failed, and how tedious the equipment is to access. Regardless of these variables, there are a few common processes that can make the technician’s life a bit easier when diagnosing a low voltage short. [Quick note: this is a guide for diagnosing a dead short in the low voltage circuit. In other words, the fuse immediately blows upon return of power to the appliance]
The first step is ALWAYS a visual inspection. You can save a lot of time and frustration by simply using good observation skills. Look for rub outs, loose connections at switches and coils, discoloration, wire splices, splits in wire insulation, etc. These can all give a technician a great starting point to searching for a short of any kind. I’ve done many visual inspections and found other issues unrelated to the short that may have gone unnoticed without thorough observation. This is why good observation skills and a thorough visual inspection is a great tool to use no matter what you’re diagnosing.
The second recommended step would be to power down the appliance and install a resettable fuse. You can find this valuable tool for cheap at any supply house, or you could even make your own from an old transformer that utilized a resettable fuse. This prevents a technician from blowing through 20 fuses before the source of the problem is found. Be careful the resettable fuse product you choose, some of them don’t trip as quickly as the factory and we have seen transformers and boards fail due to this. We suggest going to a 3A version rather than 5A when possible for additional protection.
Step three: Rule out the transformer and thermostat. These components are rarely ever the issue, but the thermostat is also one of the first things newer techs will replace when panicked and trying to solve a low voltage problem. The first quick tests will help rule them out entirely. With your meter, check primary and secondary voltage against the rated voltage on the transformer. If the transformer secondary voltage is 24v, it is typical to see a range between 22v-28v. If you measure higher or lower than normal voltage from the transformer, it may be a good idea to disconnect the transformer from the circuit and ohm out the windings and check for low resistance, which would result in higher amperage.
Remove the thermostat from the wall, and unwire all the wires except Common. Then, using either a pair of jumpers or a wire nut, connect R, G, Y, O, W wires together. Now, re-energize the system. If the fuse pops, the thermostat is NOT the problem, because it isn’t even in the circuit and the fuse still popped. If the fuse holds, and the equipment is running perfectly fine without the thermostat in place, then you may start to suspect the thermostat.
Next, remove the jumpers or wire nut and isolate R, G, Y, O, W wires from each other. Reset the fuse, and one by one jump G, Y, O, W to R. Eventually, one of those combinations will pop the fuse, and it will be in that circuit the short is located. For example, let’s say the Y wire circuit pops the fuse when jumped to R.
At this point, you’ve isolated the problem circuit, and you can begin testing everything related to that circuit. On a split system, the Y wire circuit will have the wire run from the thermostat to the indoor unit, from the indoor unit to the outdoor unit, from the outdoor unit to any defrost boards and switches, from those components to the compressor contactor. The best way to determine what is in the circuit is to read a wiring diagram, then follow the wire to verify the schematic. It is at this step a technician will repeat the visual inspection; this time more focused on a specific circuit.
Now it’s time to test all circuit components (i.e. switches, relays, contactors, circuit boards, wire splices, etc.). Look for loose connections, burn markings, bare wire, rub out locations (like wire bending over sharp edges of the chassis) etc.
If your testing leads you to suspect the wiring itself, you may isolate the wire by disconnecting the low voltage wire from the Outdoor unit completely. If the fuse still trips without any appliance connected to it (except the transformer power), then you can be certain the short is in the wire harness.
The final step in the process is to make all necessary repairs. Don’t forget to remove your resettable fuse and install a new, appropriately sized fused for the appliance! This process is one of MANY processes senior technicians have developed, and you may find yourself using your mentor’s methods, instead, and that’s perfectly fine. Just remember to always diagnose the WHOLE system! Never know what else might be happening once the short is repaired, and you can operate the system again.
For another take on a low voltage short diagnostic that comes with a little entertainment, here’s #BERTLIFE Ep. 4
If you are primarily a residential technician working on equipment under 5 tons, there are a lot of similarities between the systems you are used to and 5 – 20 ton rooftop units that are common to the light commercial market. There are MANY additional things to consider on larger equipment and here are just a few. Wash Fresh Air Filters While fresh air intake is becoming more common across the entire industry, it has been most common in commercial environments. Fresh air filters are often metal mesh and should be washed regularly with a hose and maybe some degreaser when they are in an environment near exhaust hoods. Check and Adjust Belt Tension When I was a new commercial maintenance tech I used to get belts far too tight. This would result in high amperage on the blower, belt breakage, stretching and excessive bearing wear. You want the belt to be tight enough that it doesn’t slip or vibrate excessively but no tighter. In most cases, the tension is adjusted by moving the position of the motor itself, either by way of adjusting the height of the motor base plate or sliding the base plate back and forth. In some cases, the tensioning will be done with a tensioner pulley like the one shown below. Many techs will use the 1/2″ deflection rule or something similar to guess at belt tension. The trouble is this rule doesn’t account for the length of the belt or the amount of pressure used for deflection. Many experienced techs have a good “feel” for proper belt tension, but even that can be pretty far off at times.
Browning makes a belt tension tool that you can use to ensure that the best has the proper tension for the application. Here is a quick video showing how it works. You can read the full guide on using the tool as well as proper deflection force HERE Keep in mind that belts do need to be replaced regularly. If a belt begins to loosen significantly due to stretching after the initial break-in period, it is often best to replace it rather than to keep tightening it. Align Pulleys When aligning pulleys keep in mind that you need to align the pulley centers with one another both right to left as well as the “camber” or angle of the pulleys themselves. Often pulley misalignment can happen when one of the bolts holding the motor base in place begins to slip or if a pulley has been adjusted or replaced. Misaligned pulleys and result in thrown or damaged belts, damaged bearings and noise. In addition to aligning pulleys, keep in mind that pulleys can become worn over time and lose their designed shape or wear grooves in the sides. If a pully becomes worn it will lead to improper airflow, noise and shorter belt life. Clean Condensers, Split as Needed Many commercial units have multirow condensers that will need to be split from time to time to get them completely clean. The frequency that this will be required is dependant on the location of the unit and the amount of debris in the air. Here is a video showing the process. Checking Phase Balance Many 3-phase systems will already have phase monitoring controls installed that check for voltage imbalance and dropped legs of power. This is important on 3-phase systems because even small imbalances can result in motor heat and failure. Check voltage from leg to leg on all three legs on the equipment. Any imbalance of more than 2% is considered detrimental and an imbalance of over 4% is totally unacceptable. To learn more about exactly how to measure voltage imbalance read this excellent article by John Tomczyk — Bryan
Fan laws and fan curves are a deep subject with a lot of nuance and variation. Just to get our heads around the subject let’s focus on two different types of fans that we see all the time in HVAC, the prop/axial type and the radial/centrifugal type. Centrifugal / Blower With a typical PSC blower motor (non-variable/ECM) as we increase the pressure differential across it due to any variety of factors (small ducts, dirty filter, dirty coils) the blower moves less air and it uses less power to do it. The easiest way to test this is to measure the amperage of a PSC blower with a blower door off and then measure again with it on. The current will be higher with the panel off because the static pressure is LOWER and the blower is moving more air. Take a look at this chart which shows the huge impact static pressure (and input voltage) have on airflow If you do the same test (door on then off) on an ECM constant torque or constant airflow motor the amperage will go DOWN with the door off but this is because of the motor characteristics ramping the RPM down not because of the blower wheel properties. Take a look at this chart for an air handler that uses an ECM motor. The lines of airflow to static pressure are pretty constant until the static gets above the 0.5″wc If you were to check amperage on an ECM blower you will notice it draws higher amperage the higher the static pressure across it gets due to the motor ramping up to maintain the designed flow or torque. The PSC motor is the opposite, if we increase static the airflow, amperage and wattage all drop due to the characteristics of the centrifugal blower. To Summarize –
A blower wheel decreases in power used as static pressure increases UNLESS there is a ECM motor changing the RPM to compensate
Axial / Prop A prop fan performs in an opposite way in relation to pressure. As pressure differential across it increases the power used INCREASES even as the airflow it produces decreases. This means that if you block a condenser coil the fan will move less air and draw higher amps… illustrating again why keeping condenser coils clean has a big impact on performance. To Summarize –
A prop fan “loads” more based on pressure while a centrifugal fan “loads” based on mass flow
Again… this is a simplification but for a technician understanding these relationships can help you diagnose and understand system issues. Read specific system fan charts and curves for a better look at how a particular fan performs. — Bryan
When you first start checking your supply air with a thermo-hygrometer you may notice that the relative humidity is REALLY HIGH. Often the RH in a supply duct will be between 85% and 96% relative humidity on a system that is functioning as designed. The reason for this is fairly simple.
In order for dehumidification to occur the air must reach dew point, otherwise known as 100% relative humidity
Jim Bergmann explains it this way. Think of a sponge being like air and when it is fully expanded it is like the air in the return. When the sponge is fully saturated and can accept no more water it is at 100% RH and when it is completely dry it is at 0% RH. Let’s imagine that the sponge is 50% saturated and full size in the return. When that sponge (air) goes over the evaporator coil it is compressed, because colder air can hold less moisture. Once that air is compressed (cooled) enough it will begin to give up moisture. This point at which it starts to give up moisture is called dew point or 100% relative humidity. Once that air leaves the coil it still remains in approximately the same temperature state (compressed sponge) as it was when it went over the coil. This means that unless heat is added or removed from that air, it will remain at 100% relative humidity.
So why is it less that 100% RH in the supply?
There are several reasons why the air in the supply will be slightly below 100% in the supply. First is contact factor or bypass factor which are both terms used to demonstrate the efficiency of a coil at “contacting” the air. The greater the surface area of the coil and the longer the contact time of the air on the coil the more efficiently heat will be transferred from the air to the coil.
Because no coil is 100% efficient, there will always be some air molecules that leave the coil warmer than others, this causes the airstream to be warmer overall and decreases the RH of the air stream. You will notice when a system has a higher coil air velocity (speed) it will have a higher bypass factor (lower supply humidity). When you run lower coil air velocity the bypass factor will drop and the supply RH will increase.
There is also some heat added by the blower motor and possibly even the cabinet or supply ductwork. This added dry bulb heat results in a warmer airstream and thus some additional moisture capacity. Imagine a slight expansion of the sponge due to heat from the duct walls and the blower motor.
Once that supply air exits the duct and mixes with the room air it is allowed to “expand” again and the relative humidity drops below what it was initially. This is why supply air has a high RH in cooling mode.
Here is a video we did on the topic –
This article is written by Jeremy Smith CM, experience refrigeration tech and all-around great dude. Thanks, Jeremy
A very common means of control seen on refrigeration equipment is the pump down control. Why do we use this rather than just cycling the compressor off and on like a residential HVAC unit?
Since most refrigeration equipment tends to be located outdoors, it comes down to ambient temperatures and the basic properties of refrigerant we all understand about temperature and pressure and how they can conspire to kill a compressor.
During periods of low ambient temperatures, if we were to just cycle the compressor off, it can easily get colder at the compressor than it is inside the space. If the compressor cycles off for long enough as it would during a defrost cycle, refrigerant vapor will start to condense within the crankcase. If we are lucky, the extent of this problem will be a unit that doesn’t start because the pressure of the refrigerant is lower than the cut in setting of the pressure control. What typically happens, though, is that enough refrigerant will condense to start to settle under the lubricating oil causing a lack of lubrication on restart leading to bearing wear and premature failure. If enough refrigerant condenses within the compressor housing, the resulting damage could cause valves, pistons and other internal parts to break if liquid gets into the cylinders.
How can we prevent this?
One thing that is applied across almost all sectors of our industry is crankcase heaters. These small heaters, either immersion style heaters or wrap around style heaters add a small amount of heat to help keep the compressor oil warm and help to prevent vapor from condensing there. The effectiveness of these are limited by the wattage of the heater, the ambient temperature and the size of the compressor. Too low an ambient or too large a compressor and they start to lose some effectiveness.
So, how else can we prevent condensation within the compressor? Let’s look to the pressure/temperature relationship of refrigerant for the answer. If we lower the pressure in the crankcase to a point where the saturation temperature of the refrigerant is below the ambient temperature the compressor is in, the refrigerant cannot condense. This is why we use a “pump down” type system.
In operation, a pump down control consists of little more than a liquid line solenoid valve, a thermostat control, and a low-pressure control. When the thermostat or defrost control opens, the solenoid de-energizes, stopping the refrigerant flow and allowing the system to pump the suction pressure down before the low-pressure control turns the compressor off.
How low should we set that cut-out? The Heatcraft installation manual has us setting the cut out as low as 1” Hg vacuum, depending on the minimum expected ambient. I like to set the cut in just below the lowest expected ambient temperature so that you don’t wind up in a situation like I mentioned earlier. If the ambient gets too low and the cut in is too high, your unit won’t cycle on until it warms up enough resulting in a preventable service call.
Combining a pump down control with a crankcase heater and ensuring that all controls work properly at all times can save your compressor from damage in cold weather.
Jeremy Smith, CM
The old adage goes:
“When all you have is a hammer, everything looks like a nail”
For some techs I know, even having a hammer can be challenging.
I was pretty new in business and my first real “employee” hire in the HVAC part of Kalos was my brother Nathan, who many of you know as he is quite famous or infamous in the social media circles (which it is, is for you to interpret).
We won a custom new construction home job as the HVAC contractor and this was a “custom” job to be sure. I think it may have been the first house this builder had ever built and he planned almost nothing.
I remember walking the job with him after the slab had been poured and asking, “Did the plumber run chase lines for the copper?” as it was clearly supposed to have been based on the layout, and he looks at me like I have three heads and one of them is on fire and says “What’s that?”.
We agreed that we would run line covers on the outside even though I hated to do it on a nice new house. The day arrived to run the copper and I started laying it out. The builder took one look at the covers and grunts “you aren’t putting those on the wall, those are hideous”, which they were of course (this was before the paintable plastic covers we use today). So we start walking all around the house looking for some way to pack out a wall on this concrete block house so we could punch out four line sets from the inside.
We finally settled on a spot and I started running line sets. I asked Nathan to punch through the holes in the block so we could run the lines (Yes, I would do this all very differently today so don’t ask all the obvious questions), he walks off and I don’t think much more about it.
Fifteen minutes later I round the corner to check his progress and I see him, bent over, smacking the concrete block as hard as he could with a CRESCENT WRENCH.
It’s been about twelve years since that job and a lot has changed for the better, Nathan is still the sort of guy who is more prone to use the tool in his hand rather than buy something flashy but he’s actually an incredible tech and has harnessed much of that early lack of preparedness into practical resourcefulness.
Resourcefulness and Preparedness
Accountants are prepared, they need to know every rule and have all of their I’s dotted and T’s crossed. If you throw a complicated problem at a good accountant they are prepared to take care of it with precision and if they have any questions they will make 100% sure they get them answered 100% correctly and precisely before they proceed. It’s important that they are that way to keep us out of trouble with the IRS.
HVAC techs aren’t accountants
We can prepare as best we can and sometimes something goes wrong, the valves at the rack doesn’t hold, the aluminum coil has a leak, the product is going to spoil and the Shizzle is about to hit the Fizzle.
This is why techs need to be both prepared with the proper tools, resources, materials, confidence and know-how to jump in and IMPROVISE.
Some techs use resourcefulness and improvisation as an excuse not to be prepared and others blame less than ideal circumstances when things go arwy to explain away their failure to execute.
You don’t need to choose… go ahead and do both, be both prepared and resourceful, do things by the book when you can and absolutely improvise when you must.
Practice in our field isn’t like practicing the piano for a concert. For us it’s more about learning while doing and redoing and redoing and improving every time we do rather than repeating the same mistakes and preparation errors over and over.
In our trade there are two levels of thinking, the first is always looking for what “works” and ways to get by. An example is a residential installer who knows to connect R to Red, C to Blue, G to Green and so on. He knows that when he does that and flips the breaker…. most of the time IT WORKS! He also knows about this thing called a meter, he has one in his bag and sometimes his boss tells him to poke it around in the unit a bit to “measure” some things called voltage and amperage and write the stuff that shows on the screen down on paper.
I know I sound condescending but if you are, or have been in the field you know I’m not exaggerating at all. This installer knows what works (most of the time) and he stops there. As far as he is concerned his bag is full of all the tools he needs because at the end of the day the unit usually blows cold (or hot).
We have all been there and maybe are there at one aspect of the business or another because we are just trying to scrape through a tough day without having our ignorance revealed (it’s how I feel every time I have Bergmann on the podcast).
But listen up for a second….
You never need to stop filling your skills and knowledge tool bag. NEVER!
If you haven’t tried brazing aluminum or steel before… give it a shot
Does rack refrigeration intimidate you? Look for an opportunity to work on it a bit.
You don’t learn well from reading? Guess who else didn’t… Hellen Keller, because she was BLIND and DEAF and she ended up becoming one of America’s most well known authors.
If you are good at your job and make a good living doing this stuff, CONGRATS, but that doesn’t mean you should stop growing and start allowing your brain to skills to decline.
If you are bored start doing new things like –
And the list goes on and on…
Keep adding tools to your skills toolbox, it will make your work more enjoyable, you will be more equipped to help others and you will increase your earning potential AND your ability to fix those really tough issues that has everyone else scratching their heads.
Those are the moments a good tech smiles… steps on his metaphorical (or literal) cigarette butt and digs deep into his bag of tricks… a bag that keeps growing every day.