HVAC School - For Techs, By Techs

In this episode, Bryan talks to YouTube star Stephen Rardon about combustion analysis. In Florida, we mostly have A/C units and heat pumps. High-efficiency furnaces are not in our wheelhouse, but furnaces are more like A/C units than you would imagine. Stephen Rardon makes some excellent comparisons between the two. For example, you can get an idea of how an A/C system is running without checking superheat and subcooling. With a gas furnace, you can get an idea of how it's running without checking combustion. Of course, these are both general, and you lose out on knowing the specific parameters. In a sense, oxygen (O2) and carbon dioxide (CO2) in a high-efficiency furnace can be compared to superheat and subcool on an A/C system. Going even further, we could say that a furnace's stack temperature is equivalent to airflow. Stack temperature indicates if the system is moving enough air to pull the heat off the heat exchanger. If the furnace can't adequately heat the air, then we have to look at how it's moving air in the first place. Meter clocking is a bit controversial. There is an attitude that clocking meters doesn't matter, especially among old-school techs and ones who don't have a lot of experience clocking meters. However, it is a vital step for accurate combustion analysis. Knowing how many BTUs the system is dumping is a useful measurement, especially for diagnosis. You could compare it to a delta H reading on an A/C system; the number likely won't affect the outcome, but it helps you learn more about the system. Bryan and Stephen also discuss: Stephen's HVAC YouTube journey Gas furnaces Underrated readings Fancy diagnostic tools Follow Stephen HERE. As always, if you have an iPhone, subscribe HERE, and if you have an Android phone, subscribe HERE. For 6% off of tools go to HVACRschool.com/trutech offer code = getschooled Big thanks to Carrier & Carrier Enterprise for their generous support of HVAC School.

In this unedited episode of HVAC School, Bryan and Nathan talk about some basic rules for circuit board diagnosis. So, circuit boards are boards with circuits in them. They come in two types. The traditional printed variety contains switches, relays, and resistors. The other type contains silicon chips and uses logic and processing inside the boards. You may notice these in some high-end commercial systems (EMS), but we rarely see them in residential HVAC. The diagnostic challenges come in when technicians are unfamiliar with what's on the circuit board. It helps to break it down and look at one thing at a time. Yes, there are lots of wires and relays. You may not know what it does. Take your time and get to know where everything goes and what the components are doing. Techs often misdiagnose boards because they simply don't understand how it works, and many of them don't make the effort to understand it. It may help to look at the overall purpose of the board. For example, a defrost control simply initiates and terminates defrost. It controls the condenser fan, reversing valve, and heat strips, all of which have a function in the defrost process. If you have a short on the board (no-load path), you will see arcing somewhere. You would most likely see melting on the board if that were the case. If you have a board that has failed open, the switches are closed, and there is an input. However, the board doesn't travel through the time delay to bring on the contactor. Bryan and Nathan also cover: Isolation diagnosis Best practices Pulse-width modulation (PWM) "Ghost voltages" Jumper wires vs. meters for diagnosis Blown fuses As always, if you have an iPhone, subscribe HERE, and if you have an Android phone, subscribe HERE.

Benoit Mongeau comes on the podcast to talk about high-efficiency gas furnace basics and maintenance practices. When maintaining a high-efficiency gas furnace, you typically don't have to worry about cleanliness in the same way you'd worry about an oil furnace. However, condensate drains need regular cleaning. You'll want to look for cracked heat exchangers and pay attention to your manifold gas pressure. We also have to check the temperature rise, also sometimes called delta T. Bypass humidifiers will often affect your temperature split, so that's something you need to account for in cold, dry climates; hot air will go from the supply plenum to the return. (However, corrosion typically isn't a concern for bypass humidifiers.) Water is a product of combustion, so drainage is very important to gas furnaces. Manufacturers tend to recommend that most high-efficiency furnaces be built slightly pitched to aid condensate removal. Since the combustion air contains moisture, the condensate ends up being quite acidic; that condensate is really a mix of condensed combustion products. Combustion analysis is also an important part of maintenance. If your gas burns incompletely, the furnace will end up making deadly carbon monoxide, which is the main value we measure in combustion analysis. Typically, the carbon monoxide levels should stay below 100 PPM. You can do your combustion analysis anywhere in the flue pipe as long as you're past the inducer motor. (Note: the exhaust pipe should never be above the air intake.) A liquid petroleum (LP or propane) furnace differs from a gas furnace because it has different pressure needs. You may also have to add a restriction to the burners. Benoit and Bryan also discuss: Air intake drains "Condensing" gas furnaces Inducer motor types High vs mid-efficiency furnaces Excess air Low-fire vs. high-fire gas pressure and potential effects on combustion If you have an iPhone, subscribe to the podcast HERE, and if you have an Android phone, subscribe HERE.

In this episode of HVAC School, Bryan talks with Ulises Palacios about some cool technology. Ulises has become a technology expert through his many years of working with new tools. He has recently been involved in testing new technologies, and he has worked with Jim Bergmann. Cutting open a compressor is one of the most useful diagnostic tools you can use on a failed compressor. It is also an excellent way to learn more about your equipment. They help quite often with burnouts and mechanical failures. Although winding damage is an electrical issue, other mechanical failures cause winding damage and arcs. Copper plating is relatively common in compressors. However, it makes compressor failure even more likely, as copper can be easily corroded by acid. Copper in the bearing surfaces can corrode due to moisture, manufacturer additives, and industrial byproducts in the condensing unit. Additionally, POE oil mixes with moisture to make acid. Older mineral oil (MO) does not react with moisture to the same degree. The iManifold is an expensive but convenient and helpful piece of technology. It takes the information required for the five pillars of HVAC diagnosis. It saves you time on the job site and gives you all of the readings you need. You input the tonnage, SEER rating, and refrigerant to help with diagnosis. The iManifold also syncs up to an app on your phone. Thermal imaging is not just cool. Like the iManifold, thermal imaging can also be a helpful tool for diagnosis. It can be useful for duct inspections and locating restrictions. It also doesn't have the same accuracy concerns as infrared thermometers because it compares temperatures in an area. As always, if you have an iPhone, subscribe HERE, and if you have an Android phone, subscribe HERE. Check out our handy calculators HERE.

In this episode of HVAC School, Bryan covers the basics of heat pumps. Heat pumps are common technologies in Florida. They reverse the sequence of the typical refrigerant circuit: the indoor coil can become the condenser, and the outdoor coil can become the evaporator. Heat pumps can achieve that transition via a reversing valve, which changes the directions of the suction and discharge lines. They also have two metering devices. Reversing valves contain a solenoid (typically 24v) that rediverts the suction and discharge lines via shifting the slider with a pressure differential. Pilot tubes shift gas from one side of the slider to the other, which shifts it and triggers heat mode or cooling mode. Reversing valves are typically energized in cool mode (except for Ruud/Rheem reversing valves; they energize in heat mode). Defrosting is rarely necessary for us in Florida, but it can be a scary occurrence when we do need it. The outdoor coil can freeze over entirely when it gets cold enough due to Florida's high humidity. Hot gas goes through the coils during defrosting, and it may make alarming noises. Many Floridian heat pumps also use auxiliary heat strips to provide heat while the system defrosts. Many defrosts rely on set times and sensors to determine when to initiate and terminate defrost. (That is true of heat pumps AND most refrigeration systems.) Thermistors are common sensing technologies used in defrost. Join Bryan on this informative monologue about: Reversing valves Aux heat W and W2 Heat Pumps Defrost Checking refrigerant charge in heat mode Heat mode expansion valves Common heat pump considerations For a more detailed written explanation of heat pump reversing valves with pictures, check out this article. As always, if you have an iPhone, subscribe HERE, and if you have an Android phone, subscribe HERE.

In this episode, Bryan and Nathan have a banter-filled conversation about electrical components that confuse techs. If you are looking for a serious educational episode, we suggest you look elsewhere. Low-voltage circuits may confuse the new technician because the "common" terminology is far too common in the circuit. (See how confusing it sounds in everyday use? We don't have to say "common this," "common that," but we do.) Single-phase power can also be confounding for technicians. One phase of line voltage comes in, and it gets split when it enters the circuit. That is why we also call single-phase power "split-phase" power. Another perhaps surprising area of confusion is normally open (NO) and normally closed (NC) switches. Water metaphors could potentially contribute to the confusion, as shutting off the faucet seems analogous to "closing" a circuit, but it actually has the same effect as "opening" a switch. As instructors, we need to clarify that "open" and "closed" are different from doors, faucets, etc. "Open" means that there is no path, and "closed" means that there is a path. "Normally" merely indicates the state of the switches when nothing is happening. Sometimes, transformers can be difficult to understand. A transformer is an inductive load that alters voltage and "steps it down" to a secondary voltage. Loads are what "do something" in a circuit, like a light bulb or motor. Inductive loads are magnetic (motors and transformers), and resistive loads create heat (light bulbs and toasters). Inductive and resistive loads are perfect subjects for PG-13+ metaphors, as Nathan demonstrates. Join Nathan and Bryan on a vulgar learning adventure of bad metaphors as they discuss: Relays Sequencers Inductive loads Resistive loads Blower/heat interlock Transformers Contactors As always, if you have an iPhone, subscribe HERE, and if you have an Android phone, subscribe HERE.

This podcast is a high voltage A/C electrical class that Bryan gave to some of the Kalos apprentices. The high voltage journey begins with basic electrical theory. Basically, a difference in charge is needed for electrons to move and generate power. Motors, which are inductive loads, are the greatest users of power that we will encounter in the field. Inductive loads generate magnetism and utilize alternating current (AC) power. AC power is generated by a rotating magnetic field, and the direction of the current alternates. Comparatively, resistive loads generate light and heat, and direct current (DC) moves in one direction. Theoretically, we can use Ohm's law in the field to determine the voltage, amps, or resistance (ohms) without a meter, so long as we know two of the three values. However, we may not get an accurate measurement of ohms due to reactance on inductive loads. The windings you will encounter in the field include common, start, and run. (Remember: the same side that feeds start feeds run.) In a PSC motor, the start winding stays in the circuit the entire time. When you ohm the windings, you will notice that common has the lowest resistance, run has moderate resistance, and start has high resistance. (Common to run + common to start = run to start). Universally, capacitors contain a brown, black, white, and brown-and-white wire. You can wire a capacitor in two different ways; one uses three wires, and the other uses four. The three-wire method caps off the brown-and-white wire, leaving it unused. Join Bryan and the apprentices in their high voltage class as they cover: Basic Electrical Theory Potential Difference Basic Capacitance Motor Lead identification Different motor type Motor Direction Proper Wiring MOCP and MCA As always, if you have an iPhone, subscribe HERE, and if you have an Android phone, subscribe HERE.

In this episode, Bryan talks to Justin Skinner about the standard gas furnace sequence of operation. Regardless of the furnace type, it all begins with a heat call on W... Then, the furnace checks the safeties to make sure ignition is possible and safe. If all systems are a go, the inducer motor comes on and clears a path for the exhaust. The furnace then proves that the path for the flue is clear, and a pressure switch closes upon sensing a pressure differential. The miracle of ignition comes next. There are a few different types of ignition, including hot-surface, intermittent spark, and standing pilot. Once the furnace opens the burner, it has to prove the flame. Proving flame is somewhat similar to proving the flue path. A flame sensing rod creates a potential, and it determines if a flame is present by picking up microamps of current to ground. We're merely scratching the surface here, but the bottom line is that the furnace does a lot of checking and proving throughout the startup procedure. Above all else, remember to check the fault code if the sequence of operation fails to complete. The absolute WORST thing you can do is restart the furnace, take the door off, or turn the furnace off. You lose a major troubleshooting clue. Join Bryan and Justin as they talk about these furnace sequence topics: Low Voltage Wiring Boilers Forced and Natural Draft Flame rectification Cleaning Flame Sensors Gas Pool Heat Silicon Nitride and Silicon Carbide Hot Surface and Intermittent Pilot As always, if you have an iPhone, subscribe HERE, and if you have an Android phone, subscribe HERE. Check out our handy calculators HERE.

Central Florida techs know the Southern winter all too well. Let's face it. It doesn't get super cold here regularly, but when it does, EVERYONE FREAKS. We get an abundance of service calls for unpleasant but not truly problematic conditions when people use their heaters. When people first turn on their heat, they can get a nasty surprise: a horrible dirty-sock smell and sometimes a shrieking smoke alarm. These are normal, albeit unpleasant, and do not require a service call. Another unpleasant or alarming occurrence is when a heat pump unit goes into defrost mode. Defrost mode shifts the unit into cooling mode, which may make some cold air come out of the vents. On top of that, customers may hear an awful noise and feel concerned when they see steam coming out of their unit! Pool heaters are a completely different animal in a Southern Winter, and they are often made quite poorly. You may come across gas pool heaters, propane pool heaters, heat pump pool heaters, and even solar ones. Each type has its own set of maintenance needs and varying degrees of effectiveness. When working with them, the goal is to set establish realistic expectations and explain best practices to the customer to minimize those frustrating service calls. In this episode, we talk about: Burning off heat strips Heat pump defrost mode Gas pool heater Heat pump pool heaters The thermodynamic principles of heat pump heating Defining BTUs Liquid petroleum (propane) vs. natural gas And much more... This podcast is in an unedited "meeting format" and is not usually the type of thing you will get on HVAC school, but I still think it may benefit junior techs and office staff. As always, if you have an iPhone, subscribe HERE, and if you have an Android phone, subscribe HERE. Check out our handy calculators HERE.

In this episode of the HVAC School Podcast, Bryan talks with Jeremy Smith about refrigeration tips, terms and processes. They also cover the similarities and differences between A/C and refrigeration. Being on-call as an A/C tech is not all that different from being on-call as a refrigeration tech. Similarly, the principles of heat transfer don't change between the A/C and refrigeration trades. Both trades follow the same basic rules, but all of those valves, adjustments, and tuning on rack refrigeration systems may make an A/C tech's head spin. Refrigeration techs may come across glycol chillers, rack refrigerators with several refrigerant circuits on a single piece of equipment, or piping that has been warped by hot gas defrost. There is also a greater emphasis on regulating suction pressure rather than merely measuring it, and refrigeration techs use EPR valves to help control that pressure. Each refrigerated case also has its own expansion valve. Jeremy also covers the complexity of defrost. In A/C, defrost could be as simple as shutting a unit off for a period of time. Defrost is more critical in low-temperature applications, though hot gas defrost may damage pipes and make them prone to leaks. Electric defrost typically has a lower potential to cause damage. Also, subcooling is less of a big deal in refrigeration. Sight glasses and receivers make subcooling less vital than it is in HVAC. Join Bryan and Jeremy as they discuss: Reznor startup Being on call in the refrigeration world Differences and similarities between rack refrigeration and A/C Hot gas and electric defrost Glycol refrigeration systems Subcool and superheat Refrigeration TXV settings EPR valves and their settings Rack manifold pressure And many more refrigeration tips... As always, if you have an iPhone, subscribe HERE, and if you have an Android phone, subscribe HERE. Check out our handy calculators HERE.

In this episode of the HVAC School Podcast, Bryan talks with Tim Bagnall about flowing nitrogen. Many techs don't flow nitrogen. Some may say that it is overkill, but it has been shown that flowing nitrogen displaces oxygen while brazing and prevents harmful scale from forming on the copper. Scale is very problematic, and it will likely ruin your copper lines if you keep those lines open to air. (The jury is still out as to whether climate/geography affect scale formation, though.) There are many different intensities for flowing nitrogen, particularly high-pressure purging and low-pressure flowing (2-5 SCFM). You may also have heard that you should flow nitrogen at 1.5-3 PSI, though SCFM is the preferred unit. Some best practices for flowing nitrogen while brazing include using wet towels or heat-resistant putty on the service ports, removing the Schrader cores, removing the TXV sensing bulb before brazing, and watching your torch control so that you do not overheat the metal. Join us today as we discuss the following: The proper tools and flow settings for brazing How the pressures should be set to SCFM and not PSI The possibility that geography may contribute to scale How to flow nitrogen in a practical way And much more... As always, if you have an iPhone, subscribe HERE, and if you have an Android phone, subscribe HERE. Check out our handy calculators HERE.

In this episode, Bryan goes back over the basics and stresses the importance of diagnosing the whole system. I'll cut to the chase: inspection is NOT overrated. Inspections help you become more familiar with HVAC systems and can help you catch on to minor issues before they spiral out of control. Check air filters, check the charge, check the evaporator coil... does the inspection checklist ever end? Whether you see crunchy brown contactors or oil on the lines, none of those issues are too small to warrant investigation and repair. Those may not seem worth the hassle, but a leak or low charge can negatively impact the A/C function over time, leaving you with unhappy customers. Checking everything may seem a little over-the-top, but it really is in your customers' best interest. The same goes for mundane procedures like cleaning out drains. We also have our controversial practice of the day: you don't NEED to remove a slant coil for cleaning all the time. Cleaning it in place is A-okay. Some of the system procedures I'll discuss include: Checking the charge completely Superheat and subcool Checking the evaporator coil Inspecting the filter Looking for wire rubouts Checking the drain line and drain pan Checking capacitors and contactors And much more... As always, if you have an iPhone, subscribe HERE, and if you have an Android phone, subscribe HERE. Check out our handy calculators HERE.

In this podcast episode, Bryan goes over best practices for diagnosing and replacing an A/C or refrigeration compressor. When testing for a shorted compressor, make sure the compressor is isolated from all of its circuitry. You would see low ohms to ground in a shorted compressor. Do NOT measure from winding to winding or terminal to terminal to diagnose a short. You may also come across an open winding failure. In the case of an open compressor, the power is going to the compressor, but it's not doing anything. Locked compressors also go out on internal overload and draw high amps. Try your best to unlock the compressor but be realistic about the state of compressor health. Poor compression also indicates a failure. You would typically see low head pressure and high suction pressure with low system capacity. When replacing the compressor, you'll want to start off by knowing the type of failure that was diagnosed. Reconfirm the diagnosis. Then, do your acid test and make sure you have a matching capacitor and enough refrigerant to do the job. Know your connection types, compressor model, and warranty status. Fully recover the old refrigerant charge and remove all existing driers in the system. Braze in the new compressor and pressurize the lines with nitrogen. Bubble-test all new joints and check them thoroughly. Then, pull your vacuum before adding charge by weighing a factory charge into the liquid line. When you power on the unit, monitor the performance and inspect the unit closely. Bryan also discusses: Clarification on flowing nitrogen Learning theory vs. application Pulling terminals off Proper megohmmeter use "Redneck" test (running the system without the compressor) Acid and oil testing Hard start kits and oil migration Accumulators and acid protocols Suction line driers Mufflers Vacuum pump oil If you have an iPhone, subscribe to the podcast HERE, and if you have an Android phone, subscribe HERE.

In this episode of HVAC School, Bryan covers the "5 pillars of refrigerant circuit diagnosis" and why they matter. They are: Superheat Subcool Suction pressure Head pressure Air temp split (delta T) These 5 readings give you a holistic idea of the A/C system. Instead of getting hooked on checking only superheat and subcool all the time and dismissing potential diagnoses, you can use these five readings to get an idea of the health of several parts of the system. Making it a priority to take these five readings also promotes open-mindedness, which is perhaps one of the most vital qualities of a diagnostician. The five pillars will give you the clues to diagnose overcharge or undercharge, a wide variety of restrictions, kinked suction lines, expansion valves failing open, improperly seated pistons, condenser fan issues, and so many more conditions. Also, regularly check and calibrate your tools. These 5 readings won't be helpful if you aren't constantly making sure your tools are accurate. As always, if you have an iPhone, subscribe HERE, and if you have an Android phone, subscribe HERE. Check out our handy calculators HERE.

In this episode of HVAC School, Bryan talks to his sons about basic electrical theory. Electrical theory normally requires trigonometry, calculus, and all of those fun maths. However, the basics are so easy that a 12 and 14-year old can figure it out. Electrical theory follows many of the same principles as thermodynamics—however, electrical theory concerns charges rather than heat. Conductors and insulators behave similarly with electrical charges as they do with heat. Ohm's and Watt's laws establish what volts, amps, power, and resistance, and they explain the relationships between those units. However, magnetism can add a bit of confusion to those equations. We drive motors with inductive loads, making Ohm's law seem invalid, but the magnetism resists itself, which goes unnoticed on ohmmeters. That is untrue of DC motors, and Ohm's and Watt's laws will appear to check out under most circumstances. An electrical component can fall into three main functional categories: power source, switch, or load. If something doesn't fall into one of those categories, it merely adds resistance. The power source could be a transformer, which provides homes with power from the power company (and goes from a higher voltage to a lower one that our appliances can use). A switch opens/closes or rewires an electrical path, and a load is what does the work. That's the short of it, but it's still pretty easy. Join Bryan and his sons as they talk about: Differential charges Electromotive force Ohm's law Volts, Ohms, Amps, and Watts Electrical paths Conductors and insulators Resistive and inductive loads And much more... As always, if you have an iPhone, subscribe HERE, and if you have an Android phone, subscribe HERE. Check out our handy calculators HERE.

This episode of HVAC School is a Kalos meeting where Bryan talks to his team about an incident where a leak was erroneously detected on the evaporator coil. The system was three months old, and one of our junior techs diagnosed a leak on the evaporator coil. (What?? That never happens!) So, the customer was quoted for a new evaporator coil. One week later, the charge was low again. The junior technician quoted the customer for more refrigerant charge and leak detection. The customer freaked out. Unfortunately, there were so many things we could have done to prevent the hassle and frustration for the customer. All was fine in the end, but we could have gathered more data to perform a more thorough diagnosis, sent out senior technicians to verify the issue, and kept the bigger picture of the service call in mind from the start. During this meeting, Bryan stresses the importance of: Reconfirming parts before installing them Performing a complete diagnosis Using a micron gauge Becoming a valuable technician And much more... As always, if you have an iPhone, subscribe HERE, and if you have an Android phone, subscribe HERE.

In this episode of HVAC School, we discuss the entire basic refrigerant/compression refrigeration circuit. We are in the business of moving heat. Heat refers to motion in the molecules. Temperature is the average velocity of those molecules. Heat needs a temperature differential to move. So, HVAC systems absorb heat when the refrigerant is colder than the ambient temperature. They reject heat when the refrigerant is hotter than the ambient temperature. Remember the components and their functions in the following order: Compressor: increases the vapor refrigerant's temperature and pressure. Discharge line: carries hot, high-pressure, superheated vapor to the condenser. Condenser: changes the vapor to a liquid. Liquid line: moves the subcooled (high-pressure) liquid to the metering device. Metering device: drops the liquid's pressure (creates some flash gas). Expansion line: leads the low-pressure liquid/vapor mixture to the evaporator. Evaporator: changes the liquid/vapor mix to a vapor. Suction line: moves superheated vapor to the compressor. Note: Heat pumps can shake things up a bit; the suction line becomes the discharge line (and vice versa), and the condenser becomes the evaporator (and vice versa). However, heat pumps have two metering devices and a bi-flow liquid line drier, so the liquid line stays the same. So, watch out for heat pump systems with that tricky little reversing valve. We also elaborate on some fancy accessories. These include accumulators, discharge line mufflers, receivers, and more. And we discuss much more... As always, if you have an iPhone, subscribe HERE, and if you have an Android phone, subscribe HERE.

In this episode of HVAC School, I talk with my brother Nathan... and he whines a lot about cool tools I like. As you might have guessed, Nathan is in the camp of people who believe that proper training promotes good practices; fancy tools won't make an outstanding tech. Even though I respectfully disagree with him on some things, he has a point. Tools will only be useful if a tech knows how to use them. They should make your life easier, but they shouldn't have much bearing on performance. He doesn't like wasting money or time on tools that probably won't help him. So, he doesn't like solder rings or thermal imaging cameras. On the other hand, I'm in the "tool nerd" camp. I love new technology and think tools can make us do much better work if we learn how to use them properly. On the job and in my spare time, I enjoy reading up on the latest technology and trying out the newest tools. Missing out on the newest "wow!" tools is a fear of mine. Spending money on a tool that will help me do better, more efficient work is ALWAYS worth it. I think solder rings and thermal imaging cameras are cool and can be put to good use. We talk about how efficiency, organization, training, job performance, and customer trust relate to tools. We can find some common ground in some areas, even if we have fundamentally different attitudes toward tools. Oh, and we talk about digital gauges and the jumping spider that lives in Nathan's van. —Bryan As always, if you have an iPhone, subscribe HERE, and if you have an Android phone, subscribe HERE. Check out our handy calculators HERE.

In this episode of HVAC School, Bryan talks to some apprentices about basic thermodynamics. That is the fancy scientific way of saying that we're moving heat. The way we think of "hot" and "cold" is relative to our comfort. However, the scientific concepts of "hot" and "cold" are very different from our relative understandings of those qualities. For instance, there is only ONE value of "cold" in the universe: absolute zero (0 kelvins, -460°F). Any temperature above that contains heat. Heat and temperature are NOT synonymous. Instead, heat refers to molecular motion, and temperature is an average measurement of molecular motion. Therefore, not all heat results in a temperature change. For example, adding heat to an ice cube at 32°F (0°C) changes the ice cube from a solid to liquid water. The heat added is called latent heat. Heat cannot move unless there is a differential in temperature, and it always moves from an object with more heat to one with less heat. Everything in nature tends towards equilibrium, and heat is no exception. In those cases, heat transfer will theoretically occur until both objects are at the same temperature. There are three main methods of moving heat: conduction, convection, and radiation. Conduction moves heat when a warmer object touches a cooler one. Convection occurs when heat moves through a fluid. Radiation occurs when heat moves on electromagnetic waves, such as when the sun's heat passes through a window. Join us as we cover: Heat & temperature and the difference Boiling and superheat Fahrenheit, Celsius, and Kelvin scales Absolute zero Molecular motion Hot and cold British Thermal Units (BTUs) Tons of air conditioning (and BTU/ton) Energy conversions Pressure and its effect on temperature Conduction, convection, radiation How heat transfer works in HVAC/R systems If you want to learn more about heat transfer, check out this article. As always, if you have an iPhone, subscribe HERE, and if you have an Android phone, subscribe HERE.

In this episode of HVAC School, Bryan talks to Leslie about the deceptive TXV. Thermostatic expansion valves, also known as TXVs or TEVs, are metering devices that maintain superheat. They contain an external equalizer. External equalizers give the pressure reading that you would normally take with a suction gauge at the end of the evaporator coil. They supply the closing force to the TXV. TXVs also contain a sensing bulb. The sensing bulb picks up the superheat on the suction line. When a vapor is superheated, its temperature exceeds its saturation temperature. The superheat value indicates how much the vapor temperature exceeds its saturation temperature. The bulb uses that superheat reading to adjust the TXV's opening force. System diagnosis can be tricky with TXVs, and you must set the charge by subcool on TXV systems. (Still check the superheat and follow manufacturer instructions, though.) However, TXV issues are pretty straightforward. Many of their issues deal with an undercharged sensing bulb. In those cases, you will notice issues with the opening force that acts on the valve. When replacing a valve, you typically make a new port for the external equalizer. However, getting solder in the tube can block off the closing force of the equalizer. Restrictions are also common issues for TXVs, and improper superheat is an indicator of a TXV restriction. When we think about the way TXVs manage superheat, "TXV" seems like a misnomer. We might be better off calling them "constant superheat valves" (CSVs). In addition, Bryan and Leslie discuss: Why Bryan doesn't like the name TXV Bulb, external equalizer, and spring forces Superheat and subcool Evaporator load How a TXV is supposed to work and how they fail As always, if you have an iPhone, subscribe HERE, and if you have an Android phone, subscribe HERE. Thanks to Daniel Anderson for making this his first episode suggestion.