HVAC School - For Techs, By Techs

In today's podcast, Bryan covers the four basic gas laws and how they apply to you as an HVAC technician in the field, not just in theory. Remember, when dealing with pressure, you must convert the units to PSIA, not just PSIG. To do that, you merely add 14.7 to your gauge pressure. In every equation, the "1" indicates an original value, and the "2" indicates a new value. The simplest of the gas laws was discovered first, Boyle's law. The law states that there is an inverse relationship between absolute pressure and volume. When a gas's pressure increases (such as via compression), you decrease its volume. Inversely, when you decrease a gas's pressure, that gas will expand, and its volume will increase. Mathematically, the law looks like this: P1 x V1 = P2 x V2 Charles's law focuses on volume and temperature. This gas law states that volume and temperature rise or fall together so long as the pressure stays the same. You can mathematically describe the law with the following equation: V1 / T1 = V2 / T2 The general law of a perfect gas combines Boyle's and Charles's laws. You can mathematically describe the law like this: (P1 x V1) / T1 = (P2 x V2) / T2 As HVAC technicians, we should care about the gas laws because our pressures and volumes will change as temperature changes throughout the day, such as when doing a standing pressure test with nitrogen. Nitrogen is a relatively non-reactive gas, so it will follow the gas laws and won't condense to a liquid or react with other chemicals. Dalton's law is the final law, and it states that the combined pressure of all gases in a closed space is equal to the sum of the individual gas pressures.   If you have an iPhone, subscribe to the podcast HERE, and if you have an Android phone, subscribe HERE.

Alex Figueroa is a VRF and refrigeration tech in Puerto Rico, and he talks to Bryan about his work and specialized experiences. Since Mitsubishi is a forerunner in the ductless industry, many of the units that Alex has worked on are Mitsubishi units. Alex works on lots of ductless mini-splits and VRFs in central air in commercial buildings. He typically works on VRF units that have ceiling cassettes or fan coils. Some VRF units also have branch boxes with electronic expansion valves (EEVs), and those components help distribute refrigerant flow. These systems have expansion lines, which some technicians may confuse for liquid lines. As with other large commercial HVAC units, oil is also a concern in VRF systems. Smaller-tonnage systems have large accumulators, but larger systems may also have large separators. Some of these systems are large and may contain 200-300 pounds of refrigerant. Unlike many other HVAC units, these systems have an electronic interface that indicates superheat, subcooling, and other criteria that can help with charging and troubleshooting. (Techs can, however, hook up gauges at the condenser, but the practice is not often necessary.) When you open up a VRF system for the first time, you will see lots of solenoids and other components that resemble refrigeration parts. Therefore, Alex felt that his experience as a refrigeration technician benefited him as he began working on VRFs. Like heavy refrigeration (especially grocery refrigeration), VRF systems may have several compressors and refrigerant circuits in a single system. Digital scrolls are common compressor types for these systems. The greatest maintenance issues with VRFs deal with are dirty evaporator coils and filters. In Alex's experience, the electric controls are the most commonly failed component. If you have an iPhone, subscribe to the podcast HERE, and if you have an Android phone, subscribe HERE.

What do you need to know to walk up and fix a VRF or ductless system? John Chavez, longtime VRF/ductless pro, covers his approach to ductless and VRF diagnosis in Part 2 of this podcast. (Listen to Part 1 HERE.) If you believe that there is a component failure, you'll want to check the voltage going into the unit. You'll want to pay special attention to the board and see where power is going in and out. In other words, pay attention to your inputs and outputs on the board and pay attention to the documentation in the manual. Make sure you have a quality voltmeter on hand. Another potential electrical issue occurs when the board blows out entirely. When that happens, you'll have to watch the input voltage and be mindful of the utility quality and local geography. Utility companies WILL NOT admit if they are part of the problem, so it is good for a technician to ask about the property and utilities to study the history of the unit and the location. Watch your discharge air temperatures and make sure they perform correctly under AHRI conditions (the standard is 95 degrees outdoors, 86 degrees indoors); should have 40-50 degrees coming out of the discharge of the ductless unit. Pipes may even get as cold as 37 degrees before discharge protection kicks in. To sum everything up about VRF diagnosis, you'll want to do whatever you can to find the root cause; don't be a parts-changer. To consider all possibilities, you must take your time to understand the unit. We also discuss: Lightning strikes and power surges Determining delivered capacity Critical charge Electrical/controls terminology Building science, thermal envelopes, and VRF performance Sensible and latent heat loads Inverter-driven compressors Resources Computer Room Application Formula Ductless Steps Friedrich Service Form Seven Common Install Answers If you have an iPhone, subscribe to the podcast HERE, and if you have an Android phone, subscribe HERE.

This episode covers some basics of matter that relate to HVAC/R. These basics include mass, weight, and volume. There will also be some talk of specific gravity and specific volume. Matter and energy are the building blocks of the HVAC industry; we move matter around and transfer energy. Matter refers to anything that exists and takes up space, including all solids, liquids, and gases. We use three means of measuring matter: volume, mass, and weight. Volume refers to how much space an object occupies. Even though we use mass and weight interchangeably, they mean two different things. Mass refers to the amount of matter an object has, and weight is the force exerted on an object by gravity. Density is a mass-to-volume relationship. Density comes into play when items float or sink in water, and it is a component of specific gravity. Specific gravity does not have an absolute unit of measure; it merely compares an object's density to water. For example, propane has a specific gravity of 1.5 in comparison to air and would sink. Conversely, natural gas has a specific gravity of 0.6-0.7, meaning that it would float in air. Specific volume is NOT relative; we use a set unit for it, typically cubic feet per pound. The cubic feet of air per pound changes with temperature, humidity, and barometric pressure. So, "standard air" isn't a fixed value. All gases can be compressed and can be affected by temperature much more easily than the other states of matter. Specific volume is important because it helps us determine the amount of refrigerant we can safely put into a recovery tank; you must know the difference between the specific volume of water and the refrigerant you are using.   If you have an iPhone, subscribe to the podcast HERE, and if you have an Android phone, subscribe HERE.

What do you need to know to walk up and fix a VRF or ductless system? John Chavez, a longtime VRF/ductless pro, explains his approach in Part 1 of this podcast. You CANNOT have a haphazard approach to installation or service. The best thing you can do is respect VRF and ductless technology for what they are. When you take the time to understand the equipment and the processes at work, you will be successful. The best thing you can bring to a job is patience. Unlike on typical split systems, gauges should NOT be hooked up to a ductless or VRF system unless they are absolutely necessary. Gauges may introduce contaminants into the system, and they may cause more harm than good if techs use them when they are unnecessary. Superheat is rarely a useful diagnostic reading for mini-split and multizone systems. However, superheat and subcooling are readily available readings that may be useful for diagnosing VRF systems. Diagnostic work requires detective work; ask questions about the system history to see how it has performed in the past. Involving owners in the repair process is a good way to build a relationship while understanding the problem better. Like split systems, dirty coils and air filters can severely compromise a VRF/ductless system's performance. So, try to make sure filters and coils are all clean during diagnosis. The fins of evaporator coils can get especially dirty and should be cleaned. Some ductless systems can be cleaned in place. Be sure to take down the model and serial numbers of the system. If you need tech support, you MUST have those numbers to be as specific as possible. Service and installation manuals are also useful tools for diagnosis (yes, we know that some techs are allergic to reading). However, don't over-rely on the error codes. Resources Computer Room Application Formula Ductless Steps Friedrich Service Form Seven Common Install Answers If you have an iPhone, subscribe to the podcast HERE, and if you have an Android phone, subscribe HERE. Watch the sequel to this podcast episode HERE.

Frank Besednjak talks about proper communication in conflicts between techs and managers. He also covers the potential problem with inexpensive air conditioning maintenance specials. When it comes to communication, Frank is a proponent of honesty and straightforwardness. However, he understands and appreciates the fact that people have different communication styles. He encourages people to write down their ideas, whether those ideas benefit the company, themselves, customers, etc. Frank encourages managers to set up an email or text line for people to input their ideas via written media; the leaders should make employees feel empowered to become part of the solution. The difference between a committed and complaining employee will become clear in the way that they communicate suggestions. Cultivating positivity in the business starts with future-oriented leaders. Managers who focus on the past allow negativity to breed, especially when they fixate on poor performances in the past. Frank also suggests that managers take the "good in public, bad in private" approach when discussing employee performance. The point is to find solutions, not make employees feel bad. Some PM "specials" include the infamous $89-tune-up. Some techs use these PMs as opportunities to push products and make sales. Frank believes that the pricing is not the issue; dishonesty about the tune-up's intentions is the issue. Sadly, these "specials" are often scams, but they still work for bringing in business. Some companies even do "classes" that are truly sales meetings; those meetings teach techs how to upsell and push products. This practice also opens the door for honest, skilled techs to be replaced with salespeople who do not fix units as they should. Frank recommends implementing a good pricing strategy that lets customers make their own decisions. Then, you will attract business honestly.   If you have an iPhone, subscribe to the podcast HERE, and if you have an Android phone, subscribe HERE.

Carter Stanfield, a co-author of Fundamentals of HVACR, talks about the entire refrigeration circuit. He also explains how to read and plot a pressure-enthalpy diagram. The refrigeration circuit has four main components: evaporator, compressor, condenser, and metering device. When teaching, Carter likes to explain that boiling is a cooling process and condensation is a heating process. He describes saturation as the breaking point at which liquid refrigerant can no longer hold more heat (in the evaporator). The superheated vapor from the suction line then enters the compressor; the compressor adds even more superheat. So, the discharge line has very superheated vapor. In the condenser, saturation occurs when the vapor cools to the point that it can no longer hold more moisture; the temperature stays the same until the refrigerant becomes entirely liquid. Subcooled liquid travels to the metering device via the liquid line. The metering device reduces the pressure of the refrigerant and feeds the evaporator. However, some flash gas occurs and helps drop the temperature of the remaining liquid. A pressure-enthalpy diagram illustrates the refrigerant's changes in and out of the saturated state as it moves through the refrigeration circuit. The chart looks like a curved dome, and saturated states are inside the dome. Pressure is on the y-axis, and enthalpy is on the x-axis. Pressure is a logarithmic arrangement; a linear arrangement would be impossible to plot. The bottom of the chart shows low pressures, and the top shows high ones. Enthalpy is the heat content of the refrigerant. We express it in BTUs/lb. When you plot one of these diagrams, you can start with four lines and readings: high and low-side pressure, suction line temperature into the compressor, and liquid line temperature into the metering device. You will end up drawing a parallelogram shape on the chart.   If you have an iPhone, subscribe to the podcast HERE, and if you have an Android phone, subscribe HERE.

James Bowman talks to Bryan about leak sealant products, including RectorSeal's Leak Freeze product. James talks about how sealants work, what happens when they don't work, and how to be open-minded without being gullible. Leak sealants must not react adversely with the components inside a system (oil and refrigerant). Just as mineral oil caused some issues with O-rings, POE oil has additives that cause acid to form on the system. RectorSeal's Leak Freeze is technically an oil that can work with the oil and refrigerant that already exists in an HVAC system. Leak Freeze is a high-performance lubricant that creates a soft bond around a leak and doesn't clog the system. Many refrigerant-based polymer leak sealants are hard chemicals that technically succeed at sealing leaks. However, these leak sealants are prone to clogging a system when they clot together (via flocculation). If a sealant has hazard pictograms, then there's a good chance it is a refrigerant-based sealant that creates polymers. When selecting a product, there will always be pros and cons with each product category. There are cases where each type makes sense; you must know your customers, business, and employees to determine the best choice for each unique situation. In a test that Bryan performed with Leak Freeze on a rubout leak on the high side of the system, he noticed that the sealant managed to stop the leak while the system ran. Then, the system shut off. After that, there was only a slight leak. Generally, the product was meant to work better on formicary corrosion on the low side, but it still proved to be effective at sealing a leak in a challenging location.   If you have an iPhone, subscribe to the podcast HERE, and if you have an Android phone, subscribe HERE.

Dick Wirz, author of Commercial Refrigeration for Air Conditioning Technicians, talks about making the switch from A/C to refrigeration. Dick Wirz is an advocate for using rules of thumb, which is a controversial position. However, rules of thumb are an excellent way for A/C techs to dip their toes into the refrigeration world. Rules of thumb are less likely to overwhelm technicians than the exact technicalities of certain readings and measurements. Some prime examples of using rules of thumb in air conditioning are condenser split, evaporator split/TD, subcooling, and superheat. Those all have relatively neat "rules of thumb" that don't vary too much. (30-degree condenser split, 35-degree evaporator TD, 10-degree subcooling, and 10-degree superheat.) On medium-temperature refrigerators, a common rule of thumb is a 10-degree TD for a 35-degree box with an evaporator running at 25 degrees (35 - 10 = 25). On low-temperature applications, the box temperature is -10 degrees. You still have the 10-degree TD, so the design conditions for the evaporator would be -20 degrees (-10 - 10 = -20). The pressures will vary across refrigerants, but the temperatures WILL REMAIN the same as the rule of thumb. Ice is an alarming sight for residential technicians. However, commercial refrigeration technicians will occasionally see frost or ice under perfectly normal circumstances. Frost merely indicates that the temperature of a pipe is below freezing. Ice alone does NOT indicate floodback. In commercial refrigeration, the fans run all of the time to defrost the system (even during the off cycle). However, in freezers (low-temperature refrigerators), hot gas or electric defrost is required. Dick also talks about: Subcooling vs superheat in diagnosis R-410a pressure confusion Reach-in and walk-in refrigerators Medium and low-temperature refrigerators Defrost controls Common issues in commercial refrigeration   If you have an iPhone, subscribe to the podcast HERE, and if you have an Android phone, subscribe HERE.

Camron Conlee joins the podcast to give us an introduction to ammonia chillers. He also explains what it's like to work with a poisonous refrigerant. The California division of TDI Refrigeration, where Camron works, primarily works on ammonia systems. We often see ammonia refrigeration in cold storage and food processing; ammonia refrigeration is usually in industrial applications away from the public. Ammonia is more hazardous than CO2 and other refrigerants because it is toxic. When working on ammonia chillers, the most important thing is to keep the ammonia inside the pipes. You may even need to wear full-face respirators and personal monitors when working on potentially leaky ammonia systems. Ammonia chiller oil systems are a bit different from R-22 systems. Oil separation is important in both ammonia and R-22 refrigeration, as ammonia systems typically use coalescing separation methods to isolate oil from the refrigerant. However, the oil generally doesn't mix with ammonia as readily in the first place. Some systems rely on pressure differentials to move liquid, and others use pumps to move liquid ammonia into the evaporator. Preventive maintenance on ammonia systems is quite similar to PMs on other types of refrigeration systems. Compressors are also important components that require occasional maintenance. Like many other commercial refrigeration systems, several ammonia chillers have hot gas defrost. The ammonia refrigeration world has a few different types of job opportunities. Some companies require in-house operators, but there are also external service companies, which may have a few smaller customers. In almost all cases, these jobs require technicians who can stay calm in crisis situations, as there is a lot at stake. Camron and Bryan also discuss: Recirculated vs. gravity-fed systems High vs. low-pressure receivers Dry vs. wet suction Screw compressors Copper and brass leaks Finding ammonia refrigeration companies and trade schools   Find out more about TDI at tdirefrigeration.com. If you have an iPhone, subscribe to the podcast HERE, and if you have an Android phone, subscribe HERE.