HVAC School - For Techs, By Techs

In this short podcast episode, Bryan covers why and how to test heat pump defrost during maintenance. Heat pumps need defrost because the outdoor coil absorbs heat in heating mode. Moisture collects and freezes on the coil during this process, and the rate at which it happens depends on the temperature and the amount of moisture in the outdoor air. Frost interferes with heat transfer and airflow and must be defrosted; the reversing valve shifts and auxiliary heat turns on.

Before testing, identify the equipment brand and model, defrost control, and the defrost type (time & temperature or demand defrost); you may have a thermostat (open/close switch) or thermistor, and those have different operating and testing considerations. Some controls also allow you to accelerate timing.

Forcing defrost according to the manufacturer's literature will let you discover whether the command sequence works, but it may not tell you whether the sensors are working. Common visual checks can also help you resolve defrost issues dealing with sensors, base pan heaters, and poor airflow.

The key takeaway is to pay close attention to the defrost sequence, conditions, defrost logic, sensor type, and your own spidey senses when testing or diagnosing defrost.

This episode contains embedded sponsor messages from Refrigeration Technologies, Carrier, NAVAC, Filtrete, and the 2027 AHR Expo.

Resources

• Learn Everything About Heat Pump Defrost (video)
• HVAC Defrost Troubleshooting | Timers, Sensors, and Boards (video)
• Heat Pump Defrost Cycle & Heat Strip Wiring Safety | HVAC Heating Season Preparation (video)
• How to Test Heat Pump Defrost and How Defrost Works (video)
• Upgrading Time & Temperature Defrost with Demand Defrost for Heat Pumps (tech tip)
• Heat Pump Defrost Troubleshooting Tips (tech tip)
• Coil Temp Sensors: Thermostats vs. Thermistors (tech tip)
• HVAC School calculators
• Submit a podcast question
• Learn about the GRIT Foundation

Purchase your tickets or learn more about the 8th Annual HVACR Training Symposium at https://hvacrschool.com/symposium.

In this live stream episode, Bryan sits down with Tony Gonzalez, who has spent more than 25 years at Fieldpiece and now leads the company's training department. Tony started out packing boxes in the warehouse straight out of high school, and the two longtime industry veterans use his experience to dig into why culture matters so much when you are building a business that lasts. As Bryan puts it, culture may be talked about in HVACR, but it is true everywhere.

Tony walks through TURTL, the five core values that anchor Fieldpiece's culture: Tribe, Upfront homework, Right stuff, Trust, and Lean. The missing "E" is intentional, since it reminds everyone to leave their ego at the door. He explains why values can't be purely aspirational, and how Fieldpiece keeps them alive through recognition, one-on-ones, and development reviews. Bryan shares how the same ideas show up at Kalos, including the phrase "professional pride, personal humility."

The conversation then turns to leadership, which both guests agree is where culture is won or lost. They discuss why your culture is defined by the worst behavior you tolerate, why people stay at a company, and why curiosity should come before judgment. Tony describes the "bank account" of care that makes hard conversations productive, along with the Radical Candor idea of avoiding ruinous empathy. Bryan adds that clarity is kindness and that small problems should be dealt with before they become mountains.

They close by looking at team building, using Bryan's flight crew analogy and the "right people on the bus" idea from Good to Great. Every role matters, leaders shouldn't only hire people like themselves, and snap judgments can make you overlook great talent. Bryan wraps up with a few of his leadership commitments, and Tony's final advice is to start documenting what matters to your organization, live it consistently, and give yourself grace on the leadership journey.

Topics Covered:

• Tony's 25-year career at Fieldpiece, from warehouse to head of training
• The TURTL core values and why "Turtle" has no E
• Keeping core values visible through quarterly recognition, one-on-ones, and development reviews
• Leaders as culture carriers, and how culture shows up when things go wrong
• Defining culture as a social operating system and the worst behavior you tolerate
• Professional pride and personal humility, and leaders who celebrate their team's success
• Why people stay: growth, recognition, fair compensation, and connection to the mission
• Curiosity before judgment, root cause thinking, and celebrating failure
• Making "deposits" of care so difficult conversations go well
• Radical Candor, ruinous empathy, and clarity is kindness
• Handling bad news and building a safe environment for people to speak up
• Building a flight crew: hiring for attitude, valuing different strengths, and avoiding the horns effect
• The weakest link in the chain and treating every role as equally important
• Book recommendations: Good to Great, The Power of Company Culture by Chris Dyer, and Delivering Happiness by Tony Hsieh
• Bryan's leadership commitments: truth over comfort, open doors with no gatekeeping, and people over plans

Key takeaway: leaders must live the culture, give yourself grace, and define your North Star.

This episode contains embedded sponsor messages from Refrigeration Technologies, Carrier, Copeland, Santa Fe Dehumidifiers, and TruTech Tools.

Resources

• Good to Great by Jim Collins (book)
• The Power of Company Culture by Chris Dyer (book)
• Delivering Happiness by Tony Hsieh (book)
• HVAC School calculators
• Submit a podcast question
• Learn about the GRIT Foundation

Purchase your tickets or learn more about the 8th Annual HVACR Training Symposium at https://hvacrschool.com/symposium.

In this short podcast episode, Bryan discusses electrical connections and whether tighter is better (or if a connection is tight enough to fail).

Torque is a turning effect; force is applied at a distance from the screw's center, and that force creates pressure at the connection. A quarter-turn doesn't tell us how much force we have applied. You may notice a tight screw with other signs of a poor connection, like discoloration; tightening the connection may not help.

At a connection, we want very little resistance to current flow, and we get increased resistance and heat where we don't want it when connections are poor; according to Watt's law, when the resistance stays the same, doubling the current creates four times the heating power. However, temperature alone doesn't tell you the cause; thermal imaging is useful evidence, but we need operating conditions and current measurements, too.

The key takeaway is that tightening the connection as much as possible may do more harm than good; having a torque screwdriver and using it can help. When making new connections, use the torque screwdriver to torque to the proper specs right out of the gate. We must also consider wire sizing, wire placement, exposed conductors, and unacceptable double lugging. We must also be mindful of ferrules, including proper selection and crimping. Make all adjustments safely (without voltage), and if you do not have the manufacturer's data immediately available, look it up. Eventually, you will get an idea of what "good" looks like.

Remember: tighter doesn't necessarily mean better.

This episode contains embedded sponsor messages from Refrigeration Technologies, Carrier, NAVAC, Filtrete, and the 2027 AHR Expo.

Resources

• Tightening Electrical Threaded Terminal Connections (tech tip)
• HVAC School calculators
• Submit a podcast question
• Learn about the GRIT Foundation

Purchase your tickets or learn more about the 8th Annual HVACR Training Symposium at https://hvacrschool.com/symposium.

Glycol secondary loop systems are showing up in more and more grocery stores, and in this episode of the HVAC School Podcast, Bryan Orr sits down with Max, one of the company's lead startup techs and its in-house subject matter expert on glycol skids. Max explains what these systems are, why clients are choosing them for retrofits, and what it takes to commission one without taking a live store down. The big picture: a traditional DX rack chills a water and propylene glycol mix in a heat exchanger, and that glycol is pumped around the store to cool the medium-temperature cases.

The conversation starts with the "why." Reduced refrigerant charge inside the building, keeping flammable or higher-GWP refrigerants out of the sales floor, regulatory pressure, and zero-emissions initiatives all push clients this way. Max is upfront that efficiency isn't one of the reasons at this scale, since the extra heat exchange step, lower suction temperatures, and pump energy all cost something. He also covers the trade-off in reliability: case-level controls are simple, but a fault in one of the skid's main valves can take out every case at once, so techs have to move fast.

From there, Max walks through the skid itself, from the brazed plate heat exchanger, VFD-controlled pumps, and air separator to the expansion tank, strainers, suction guide, controller, and EEV drivers. He then covers flow control with balance valves, defrost strategy, and the importance of proper vents and drains in the piping. The two get into the details of startup and commissioning, and some key takeaways include pressure testing instead of pulling a vacuum, filling and purging air, and verifying that the refrigerant-side valves are wired and driven correctly so a swapped valve doesn't flood the rack.

The back half of the episode is practical field advice. Max shares how to recognize air in the loop, why store humidity and dew point matter so much for case performance, which specialty tools and fittings he carries, and how to handle glycol mixing and top-offs.

Topics Covered

• What a glycol secondary loop system is, and how it differs from direct expansion
• Why retrofits are happening: refrigerant charge reduction, safety, EPA regulation, and zero-emissions goals
• Efficiency penalties at small scale, and why efficiency isn't the driver
• How glycol behaves in the coil: no latent exchange, a temperature gradient, and frost patterns
• Reliability trade-offs: simple case controls versus centralized, mission-critical valves
• Staging a retrofit so the store stays open, including pre-piping, pre-testing, and pipe cleaning
• Brazing versus soft solder, and whether nitrogen flow matters with glycol
• Skid components: heat exchanger, VFD pumps, air separator, feeder tank, expansion tank, strainers, and suction guide
• Controller inputs, EEV drivers, and emergency mobile chiller connections
• Balance valves (automatic versus manual) and defrost methods, including off-time and electric
• Fluid distribution: pitching pipe for air and drainage, plus vents and drains
• Propylene versus ethylene glycol, the 35% mix, freeze point, and why more glycol hurts heat transfer
• CO2 as a secondary fluid for low-temperature applications
• Commissioning steps: electrical checks, pressure testing, filling, purging, and testing valve operation
• Proving performance: flow, glycol concentration, temperature, and superheat on the rack side
• Troubleshooting air in the system and pressure changes as glycol chills
• Store humidity, dew point targets, and case performance
• Heat reclaim using glycol loops
• Tools: PT ports, manometers, female-to-female hoses, refractometer, and transfer pumps
• Service tips: distilled water, matching glycol brands, and glycol safety

This episode contains embedded sponsor messages from Refrigeration Technologies, Carrier, NAVAC, and Filtrete.

Resources

• HVAC School calculators
• Submit a podcast question
• Learn about the GRIT Foundation

Purchase your tickets or learn more about the 8th Annual HVACR Training Symposium at https://hvacrschool.com/symposium.

In this short podcast episode, Bryan talks about why your thermostat is reading the wall, not the actual air temperature.

A thermostat is an instrument designed to read temperature (and sometimes humidity); it displays those readings based on sensors and makes decisions. Most of these sensors are thermistors, which are resistors that change resistance with changes in temperature. Thermistors have low mass and respond to radiant, convective, and conductive heat.

Air coming through the wall (convective heat), the temperature of the things around the thermostat (radiant heat), AND the wall temperature (conductive heat) can influence your thermostat's reading. We may see a service call where the thermostat reads above the air temperature and runs the air conditioning unit even when the air temperature is already below the set point. Our first move as technicians should be to ask customers when they noticed the problem; the timing can give us some clues about what is going on. Looking behind the thermostat is one of the first things we should do, as air can move through the hole where wires come through, especially if there is air leakage elsewhere. If there is a temperature difference and an airflow path, that could be the source of the issue.

Use a reliable temperature probe near the thermostat, off the wall and away from the thermostat casing and electronics, to get a reliable temperature measurement to compare to the thermostat. If the probe and thermostat disagree after several minutes, we should investigate deeper for a warm wall. Infrared thermometers and thermal imagers can help you identify warm surfaces. Keep in mind that thermostats may have sensors in different locations, offsets, and programmed corrections as well.

If you find an open wire penetration, use non-flammable insulation and/or an appropriate putty to close it. Be careful not to block the sensing vents, too. Let everything settle and repeat the comparison. Some other solutions include changing the location of the thermostat or remote sensor.

This episode contains embedded sponsor messages from Refrigeration Technologies, Carrier, Copeland, and Santa Fe Dehumidifiers.

Resources

• HVAC School calculators
• Submit a podcast question
• Learn about the GRIT Foundation

Purchase your tickets or learn more about the 8th Annual HVACR Training Symposium at https://hvacrschool.com/symposium.

In this episode of the HVAC School Podcast, Bryan sits down with Chris Howells, senior training manager at AprilAire, to talk about what really makes a filtration system perform. Chris has nearly thirty years in the industry, including fifteen as a technician, and brings a field-first perspective on why filtration is more than just "a filter." Bryan also admits up front that his own contracting company is looking to put more high-efficiency filters into the field, so this conversation doubles as a practical learning session.

The discussion starts with a common misconception: that a "thicker" filter is simply a filter with thicker media. Chris explains that what matters is surface area, face velocity, and pressure drop, not the width of the cabinet. They cover why using the full face of the filter is one of the easiest wins, how a poorly designed return can load just one section of the media, and why a high MERV rating does not automatically mean high resistance. Cabinet design, media construction, and overall system design all play a role, and modern ECM blowers make low static pressure more important than ever.

From there, the conversation turns to bypass air and measurement. Chris describes how AprilAire's cabinets use top and bottom rails and a self-seal media overhang to force air through the filter, backed by a 10-year clean coil guarantee. He and Bryan stress using the right tools, including a dual-port manometer and a proper static pressure probe, and checking pre-filter and post-filter pressure drop against manufacturer performance data at around 500 feet per minute. Chris also debunks the idea that deeper media is always more restrictive, pointing out that a typical retail one-inch pleated filter can raise pressure drop dramatically compared with a basic fiberglass filter.

The final stretch is about communication and growth. Chris and Bryan share simple, natural questions technicians can use to start air quality conversations without sounding like a sales pitch, and they encourage listeners to stay curious and keep asking "why." Chris closes with resources for learning more, including AprilAirPartners.com and the AprilAire Academy, and mentions that the Santa Fe and UltraAire product lines are now part of the AprilAire family.

Topics Covered

• Why "thicker" filters are really about surface area, face velocity, and pressure drop
• Using the full face of the filter and avoiding uneven loading
• How filters affect blower performance, system capacity, and equipment protection
• Why filtration is a high-value upgrade compared with bulbs and modules
• AprilAire's new high-efficiency product line and its three-layer media design
• Reducing bypass air with rail design, self-sealing media, and the 10-year clean coil guarantee
• Measuring static pressure correctly and using manufacturer pressure drop charts
• Sizing media cabinets by CFM and face velocity instead of what fits under the air handler
• Common myths about MERV ratings and restriction
• Conversation starters that help technicians talk about indoor air quality
• How to learn more through AprilAirePartners.com, the AprilAire Academy, and local distributors

This episode contains embedded sponsor messages from Refrigeration Technologies, Carrier, Copeland, Santa Fe Dehumidifiers, and TruTech Tools.

Resources

• AprilAire Partners
• HVAC School calculators
• Submit a podcast question
• Learn about the GRIT Foundation

Purchase your tickets or learn more about the 8th Annual HVACR Training Symposium at https://hvacrschool.com/symposium.

In this short podcast episode, Bryan talks about the fuse that only blows when you leave. The service call usually goes like this: you replace a blown fuse, the system runs fine, you leave, and then the fuse blows again. There could be several causes of a blown fuse.

First, ask what was happening right before the system stopped, such as if the unit was starting up, if it was raining outside, or if the operating mode changed. The customer may not know the specifics, but they may be able to offer a clue. If the control fuse blows during a specific call, we may be able to locate a short in one of the circuits involved. We may also be able to find out a bit by inspecting places where wire often gets damaged, such as common points where conductors pinch or rub.

Isolation diagnosis can help us isolate the specific circuit or component with a problem. First, look at the wiring diagram, label conductors, and take pictures of the original setup before disconnecting anything. Keep the correct fuse protection instead of using a larger fuse, leave all safety controls in the circuit, and use the manufacturer's test procedure if it's available. Then, isolate different loads and conductors so they can be energized individually; some modern thermostats make this easy. Also note that continuity testing alone isn't always reliable for locating problematic paths.

Sometimes, motion (from motors), temperature, and moisture can also contribute to intermittent issues. Additionally, some inductive loads, like contactor coils, experience unique intermittent issues that cause the components to draw high current; inductive reactance matters. Measuring current on the different circuits as you energize them can also point you toward circuits that have higher current than expected.

Once you've found and repaired something, go back to the condition that made it fail. Make sure you fix the underlying problem, such as exposure to excess heat, vibration, or moisture.

This episode contains embedded sponsor messages from Refrigeration Technologies, Carrier, Fieldpiece, TruTech Tools, and Filtrete.

Resources

• Isolation Diagnosis (tech tip)
• HVAC - Isolate to Diagnose (video)
• HVAC School calculators
• Submit a podcast question
• Learn about the GRIT Foundation

Purchase your tickets or learn more about the 8th Annual HVACR Training Symposium at https://hvacrschool.com/symposium.

In this episode of the HVAC School Podcast, Bryan welcomes back Bill Spohn to talk about carbon monoxide and a troubling trend in the alarms being sold online. They start with the basics: the difference between a standard UL 2034 alarm and a true low-level CO monitor. UL 2034 alarms were designed to avoid nuisance calls, so they can stay silent through long exposures at relatively low concentrations. Low-level monitors are far more sensitive and can warn you that something is brewing before it becomes a life-threatening emergency.

Bill explains why that gap matters, walking through how carbon monoxide displaces oxygen on hemoglobin, why it lingers in the body, and why children, older adults, and people with heart or lung conditions are especially vulnerable. Bryan adds the troubleshooting angle: a UL 2034 alarm is the safety net that keeps people from dying, but low-level monitoring helps you find and fix a problem early, much like catching a refrigerant leak before the system is flat.

The conversation then turns to the main story. Bill bought a pair of inexpensive alarms advertised as both low-level and UL 2034 compliant, which is a contradiction, since the two cannot be the same device. They arrived with no instructions, no model number, and no visible certification control number, and they closely resembled a product tied to a Consumer Product Safety Commission warning covering roughly 375,000 units and 91 reported failures to alarm. Bill traces the marketing back to what appears to be a single factory selling under many brand names, backed by a virtual office address, a fake firefighter endorsement, and a flood of promotional emails.

Bryan and Bill close with lessons for technicians, consumers, and manufacturers alike. Be skeptical when price and performance seem too good to be true, verify who is behind a brand, and remember that claiming to meet a standard is not the same as being independently certified. They also urge established manufacturers to be humble, test claims thoroughly, and make sure published specifications reflect how their sensors actually perform.

Topics Covered

• Low-level CO monitors versus UL 2034 alarms, and why they are not interchangeable
• How the 1990s Chicago nuisance-alarm events led to the UL 2034 standard
• Why standards built around healthy adult males leave gaps for vulnerable people
• How carbon monoxide binds to hemoglobin and why it accumulates in the body
• Why "CO leak" is the wrong phrase: carbon monoxide is created, not transported
• Online alarms claiming to be both low-level and UL 2034 compliant
• The Consumer Product Safety Commission alert and the 91 reported failures to alarm
• Red flags: no instructions, no model number, no certification mark, a virtual-office address, and a fake endorser
• What the alarm test button actually checks (the circuit and horn, not CO response)
• The challenge of validating alarms without accessible CO test kits
• How to vet unfamiliar brands, including using AI to research price, company history, and website age
• Sensor signal smoothing and why muted low-end readings can mislead users
• A call for manufacturers to test in the field and for honest specification claims
• Why price alone should never drive the purchase of life-safety devices

This episode contains embedded sponsor messages from Refrigeration Technologies, Carrier, White-Rodgers by Copeland, Santa Fe Dehumidifiers, and TruTech Tools.

Resources

• HVAC School calculators
• Submit a podcast question
• Learn about the GRIT Foundation

Purchase your tickets or learn more about the 8th Annual HVACR Training Symposium at https://hvacrschool.com/symposium.

In this short podcast episode, Bryan talks about what happens when you adjust the condenser airflow: you have the same charge, different numbers. This short covers HVAC condensers and flooded condensers in refrigeration applications.

When you increase condenser airflow by repairing a condenser fan or washing the unit, the pressure and subcooling readings change even though the charge stays the same. Refrigerant enters the condenser as superheated vapor and goes through three stages: desuperheating, condensing, and subcooling. The key thing to remember is that these three stages can occur at different points of the condenser as the operating conditions change.

Higher head pressure doesn't necessarily lead to higher subcooling, as subcooling depends on both saturation temperature and actual liquid temperature; if both change, head pressure can't tell us which way subcooling went. Exceptionally bad airflow across the condenser and high compression ratios can also interfere with liquid delivery. Uneven condenser airflow distribution also affects refrigerant distribution in the condenser. We shouldn't use low subcooling as an automatic indicator to add more charge.

If there's one thing to remember, it's that you need to fix the airflow problem before deciding there is a charge problem. Operating readings can change without the total refrigerant charge changing.

This episode contains embedded sponsor messages from Refrigeration Technologies, Carrier, NAVAC, Fieldpiece, and Filtrete

Resources

• NIST: Effect of Common Faults on the Performance of Different Types of Vapor Compression Systems
• NIST: Performance of a Residential Heat Pump Operating in the Cooling Mode with Single Faults Imposed
• University of Padua: Condenser Airflow and Refrigerant-Inventory Modeling
• Condenser Fan Blade Shroud Depth (tech tip)
• Condenser Fan Blade Placement (tech tip)
• HVAC School calculators
• Submit a podcast question
• Learn about the GRIT Foundation

Purchase your tickets or learn more about the 8th Annual HVACR Training Symposium at https://hvacrschool.com/symposium.

Some people light up when they find a difficult electrical problem. Others want a wrench in their hand or take real satisfaction in a beautifully planned installation. Those differences can shape how we learn, what frustrates us, and where we find satisfaction in HVAC work.

Bryan and Bert explore three overlapping tendencies in the trades: the technician, the mechanic, and the craftsman. In their framework, technicians gravitate toward diagnosing problems and understanding hidden causes. Mechanics engage with the physical work of repairing and assembling equipment. Craftsmen bring careful preparation, spatial planning, and pride in the finished result. Most people have some of each, and experience can build skills across all three.

The conversation also covers comfort with chaos and Bryan's distinction between moralizers, who feel a strong pull toward how things should be, and normalizers, who work readily with conditions as they are. Both approaches have strengths and blind spots, especially when a job needs a mix of planning, troubleshooting, and execution.

For owners, trainers, and field leaders, the practical question is how to recognize what energizes a person and give them opportunities to use it. Bryan and Bert discuss apprentice training, promotions that move people away from work they enjoy, and the value of building crews with complementary strengths. They close with mentorship and gratitude for the people whose abilities make our own work possible.

Key Takeaways

•

Observe apprentices across different tasks. Troubleshooting, assembling a training board, and hands-on installation can reveal different interests. Notice the questions people ask, the work they stay absorbed in, and the details they care about.

•

Separate ability from inclination. A person can develop a skill and still find that work draining. Talk about what brings energy and satisfaction before assuming the next promotion is the right fit.

•

Pay attention to frustration. Uncertainty, interrupted preparation, repetitive work, and physical challenges affect people differently. Use those patterns to start better conversations about training, support, and job assignments.

•

Build complementary teams. A crew benefits from people who can diagnose, people who readily tackle the physical work, and people who plan and execute careful details. Recognize the contribution each person makes.

•

Value mechanical skill alongside technical knowledge. Bryan makes the case that the willingness and ability to get physical work done deserve more recognition as information becomes easier to access.

•

Make room for mentorship. Experienced tradespeople can multiply their impact by helping others develop similar strengths, even as the physical demands of daily fieldwork become harder to sustain.

Chapters

00:00 — Three ways to thrive in the trades 10:10 — Chaos tolerance and work preferences 12:45 — Moralizers and normalizers 18:15 — What craftsmen care about 22:15 — Ability, energy, and burnout 24:00 — Recognizing strengths in apprentices 31:20 — The changing value of mechanical skills 39:35 — Building teams with complementary strengths 44:25 — Mentorship and a longer career in the trades 46:05 — Appreciating your strengths and your teammates

This episode contains embedded sponsor messages from Refrigeration Technologies, Carrier, NAVAC, Fieldpiece, and the 2027 AHR Expo.

Resources

• HVAC School calculators
• Submit a podcast question
• Learn about the GRIT Foundation

Purchase your tickets or learn more about the 8th Annual HVACR Training Symposium at https://hvacrschool.com/symposium.

A liquid-line restriction should cause high subcooling, right? Not always. In this short episode of the HVAC School podcast, we look at why normal subcooling does not rule out a restriction and why one familiar diagnostic pattern cannot tell the whole story.

Subcooling describes the refrigerant's temperature margin below saturation at a particular location. It does not directly measure how much refrigerant is stored in the condenser or prove that the metering device is receiving adequate liquid. A thermostatic expansion valve may compensate for a moderate restriction by opening farther, while a receiver can provide another place for liquid to collect. Incorrect charge, poor airflow, and other faults can also exist alongside a restriction.

The practical lesson is to follow the liquid all the way to the metering device. Pressure losses through tubing, filter-driers, valves, and vertical rises can affect liquid delivery even when the reading at the outdoor unit looks normal. Temperature differences across a filter-drier can be useful clues, but a pressure drop may be difficult to detect with temperature clamps while the refrigerant remains subcooled liquid. The episode also discusses flash-gas clues, sight glasses, and the importance of inspecting the actual refrigerant path before settling on a diagnosis.

The key takeaway is that normal subcooling at one measurement point does not clear the entire liquid line. Follow the refrigerant path and consider the equipment, valve response, receiver, and other operating evidence together.

Topics Covered

• Why a liquid-line restriction can occur with normal subcooling
• Subcooling as a temperature margin rather than a measure of stored refrigerant
• How expansion-valve response can mask a moderate restriction
• How receivers change refrigerant storage and the diagnostic picture
• Why multiple faults can exist at the same time
• Pressure losses between the condenser and the metering device
• The limits of temperature checks across a filter-drier
• Flash-gas clues, sight glasses, and liquid quality versus pressure
• Avoiding kinks, excessive line-set rise, and overlooked filter-driers

This episode contains embedded sponsor messages from Refrigeration Technologies, Carrier, NAVAC, Filtrete, and the 2027 AHR Expo.

Resources

• Liquid Line Temperature (video)
• HVAC School calculators
• Submit a podcast question
• Learn about the GRIT Foundation

Purchase your tickets or learn more about the 8th Annual HVACR Training Symposium at https://hvacrschool.com/symposium.

In this episode from the 7th Annual HVACR Training Symposium, Alex Meaney delivers a live conference talk he calls "Airflow Serenity," built around the idea of knowing which duct problems are worth chasing and which changes will actually move the needle for a customer.

He opens by describing and reframing how technicians identify airflow problems, including the "complementary failure" situation where both the ductwork and the equipment are improperly sized. The way we communicate with homeowners plays a massive role in how well we can identify these problems. The time spent learning about a homeowner's comfort complaints is a sales tool in itself.

The middle of the talk is where the technical takeaways come in, including how to measure system airflow with anemometers, manometers with static pressure probes & a blower chart, and the TrueFlow Grid. The main engineering takeaway is that friction, not duct size alone, governs airflow, and that friction increases with the square of velocity — so relatively small increases in duct size or reductions in restriction along the path can produce outsized gains.

There are several practical, low-cost fixes technicians can make: pulling slack out of flex duct, adding return capacity, using proper transitions and radius fittings instead of abrupt ones, avoiding compound fittings, and making sure supply plenums have a proper end cap rather than dead-ending against a wall. These can be bundled into a system replacement.

This episode contains embedded sponsor messages from Refrigeration Technologies, Carrier, Copeland, Santa Fe Dehumidifiers, and TruTech Tools.

Resources

• Mean HVAC Consulting & Design (Alex's website)
• HVAC School calculators
• Submit a podcast question
• Learn about the GRIT Foundation

Purchase your tickets or learn more about the 8th Annual HVACR Training Symposium at https://hvacrschool.com/symposium.

In this short podcast episode, Bryan talks about compression ratio and compressors, particularly why you see more suction pressure when the compressor unloads and what that means for the HVAC system's operation.

When the compressor drops into low-stage or unloads, the suction pressure goes up. Regardless of the cause of reduced pumping, the head pressure will also drop as the suction pressure rises. If the conditions stay the same and the compressor stages down, the pumping capacity drops; the compressor moves less vapor while the evaporator still needs to absorb the same amount of heat.

However, if the indoor airflow also drops along with the compressor stage, the load on the evaporator also changes and drops the suction pressure. Dynamic metering devices (such as TXVs and EEVs) also need to equalize and factor into the compression ratio.

We should understand the sequence before condemning a compressor and then use that sequence in diagnosis. To troubleshoot and test staging, we want to identify the equipment and sequence (including how the manufacturer wants us to test staging) and then record everything at each stage or at least a few different points. We want to see how the equipment responds, such as if one part does not respond when the compressor drops to a lower stage.

This episode contains embedded sponsor messages from Refrigeration Technologies, Carrier, NAVAC, TruTech Tools, and the 2027 AHR Expo.

Resources

• Compression Ratio (video)
• Why Compression Ratio Matters (tech tip)
• HVAC School calculators
• Submit a podcast question
• Learn about the GRIT Foundation

Purchase your tickets or learn more about the 8th Annual HVACR Training Symposium at https://hvacrschool.com/symposium.

In this episode, Bryan welcomes back Louise Kellar of UEi Test Instruments for a deep dive into getting more out of a digital clamp meter than the basic volts, amps, and ohms most techs rely on every day. The tool in the spotlight is UEi's High Accuracy Clamp Meter (HAC), which is accurate when dealing with the low current draws common on modern condenser fan and blower motors and is critical for reliable wattage and capacitor-under-load testing.

The podcast also walks through a series of lesser-used but valuable meter functions, including microamp measurement for flame rectification testing, diode testing for diagnosing boards on mini-splits, the Low Z setting for eliminating ghost voltage readings and safely bleeding capacitors, and the safety-locking temperature toggle that prevents technicians from accidentally crossing voltage and thermocouple leads.

Bryan and Louise also cover common mistakes, such as not knowing when to use continuity or resistance and auto-ranging mistakes, as well as some crucial takeaways about true RMS measurements, temperature settings, and CAT safety ratings.

This episode contains embedded sponsor messages from Refrigeration Technologies, Carrier, NAVAC, and Filtrete.

Resources

• UEi products, manuals, and resources
• HVAC Multimeter Skills: Continuity vs. Resistance & Diode Testing (video)
• CAT Ratings on Electrical Multimeters (tech tip)
• HVAC School calculators
• Submit a podcast question
• Learn about the GRIT Foundation

Purchase your tickets or learn more about the 8th Annual HVACR Training Symposium at https://hvacrschool.com/symposium.

In this short podcast, Bryan and Roman discuss premature coil failure in ductless mini-splits and VRF equipment.

These coils are susceptible to a few different types of corrosion. Warmer coil saturation temperatures and shorter runtimes result in lower latent capacity; whatever moisture is on the coil dries on the coil instead of draining out. Minerals and chemicals (including chlorides from bleach or cleaners) interact with the coil and may cause corrosion, including formicary ("ant's nest") corrosion. Leaks and corrosion may be environmental rather than entirely attributable to manufacturer defects.

Technicians can use proper cleaners with correct dilution ratios and rinse the coils. In situations where the environment contributes to coil corrosion, such as with substances off-gassing or dealing with coastal air, we will need to dilute the pollutants by ensuring proper ventilation. Dilution needs to be intentional, especially in hot-humid climates, and ventilating dehumidifiers with good filtration may be a good move. Source control and filtration are also good mitigation strategies, and clear, open client communication can help clients understand the problem and make informed decisions about their HVAC system.

This episode contains embedded sponsor messages from Refrigeration Technologies, Carrier, NAVAC, and Fieldpiece.

Resources

• Coil Corrosion w/ Kevin Hart and Bryan Orr
• Living in a World of Acids (and why HVAC coils are secretly crying for help)
• HVAC School calculators
• Submit a podcast question
• Learn about the GRIT Foundation

Purchase your tickets or learn more about the 8th Annual HVACR Training Symposium at https://hvacrschool.com/symposium.

In this live episode, Bryan sits down with Jim Bergmann of measureQuick and NAVAC trainers Zane and Jesse Stewart for a deep, technician-focused conversation about advanced refrigerant recovery. The group covers diverse system types and environments, including low-ambient recovery.

Recovery machines cannot pump straight liquid, which we need to be mindful of during service. That said, vapor-only recovery works fine for small charges, but push-pull recovery becomes worthwhile once a system holds more than roughly ten pounds of refrigerant. Refrigerant and tank contamination, as well as general safety (including tank fill limitations), are a couple of other field challenges worth considering in our recovery best practices.

Some best practices to take away from this episode include attaching to the vapor side of the tank (and inverting it), pulling Schrader cores, using large hoses instead of manifold gauges, and keeping the recovery tank cool to eliminate restrictions.

This episode contains embedded sponsor messages from Refrigeration Technologies, Carrier, Copeland, Santa Fe Dehumidifiers, and TruTech Tools.

Resources:

• Don't Overfill Recovery Tank Cylinders the Easy Way
• Recovery Tank Safety
• Recovery Tank Capacity
• Push-Pull Recovery
• Recovery Best Practices w/ NAVAC
• HVAC School calculators
• Submit a podcast question
• Learn about the GRIT Foundation

Purchase your tickets or learn more about the 8th Annual HVACR Training Symposium at https://hvacrschool.com/symposium.

In this short podcast episode, Bryan and Roman talk about the A2L & refrigerant transition again, particularly sensors on R-454B and R-32 equipment.

Since the beginning of the A2L transition, we have seen the equipment evolve and begin requiring accessories, including refrigerant sensors and blower recirculation systems (BRS) or dissipation boards. In a BRS, the blower turns on and dilutes the refrigerant in the space to keep the refrigerant concentration below the lower flammability limit (LFL) and prevent ignition. Some systems may also have isolation valves and pump themselves down whenever the A2L sensor trips. These sensors use MOS technology, which measures gas changes by tracking electrical connectivity shifts; they have limited lifespans and can become corrupted over time.

In the field, you may notice a running fan without the outdoor unit running. Some diagnostic boards might give you error codes, but if you don't and don't have 24V when you troubleshoot the issue, you may want to check the sensor. The sensors could be wet, tripped by VOCs, or even have been cut out.

This episode contains embedded sponsor messages from Refrigeration Technologies, Carrier, TruTech Tools, Fieldpiece, and Filtrete.

Resources

• A2L Dissipation Boards and Leak Sensors
• HVAC School calculators
• Submit a podcast question
• Learn about the GRIT Foundation

Purchase your tickets or learn more about the 8th Annual HVACR Training Symposium at https://hvacrschool.com/symposium.

In this episode, Bryan sits down with Mike Pastorello, owner of Refrigeration Technologies, and Ashley Lynds, director of education and brand management for Viper, to talk about the company's roots, its newest product launches, and where the brand is headed next. This podcast focuses on "The Lab" and how it integrates field technicians with product development.

Refrigeration Technologies was built on a "for techs by techs" philosophy after John, an HVAC technician with a chemistry background, began inventing products to solve his own field problems. Now, technicians are using their field problems to inspire innovation in the Refrigeration Technologies lab, and the Easy Dose is the first product that was developed, tested, and distributed via the "Lab" initiative.

The team also discusses chemical safety in their approach to products and what's really inside products like the Viper Pan & Drain Treatment and Nylog.

This episode contains embedded sponsor messages from Refrigeration Technologies, Carrier, NAVAC, Fieldpiece, and AHR Expo 2027.

Resources:

• Refrigeration Technologies
• AHR Expo
• Careful With Cleaners
• HeatShield Demo
• HVAC School calculators
• Submit a podcast question
• Learn about the GRIT Foundation

Purchase your tickets or learn more about the 8th Annual HVACR Training Symposium at https://hvacrschool.com/symposium.

In this short podcast episode, Bryan and Roman talk about the ethics of IAQ, particularly in terms of microbial growth testing vs. remediation conflicts, based on Roman's recent experience hiring a mold assessor and then a remediation expert in his home. Remediation is governed by S520 of the IICRC.

Microbial growth is tricky because it is often hidden and has real health effects, but there is a history of fraud in its assessment and remediation. To help combat that fraud, in Florida, assessment and remediation are two separate practices with two separate licenses. Roman got to see the differences in action by working with different assessment and remediation professionals and witnessing how the two practices depend on each other but differ.

First, an assessor came to Roman's house with testing equipment and a means of collecting lab samples; this assessment started outdoors and continued indoors, and the assessor produced a thorough 87-page report with the tool findings, lab findings, and pictures. As with HVAC, the results are based on science and data, and reputable assessors are licensed, independent, and have the tools and training to carry out the job without using scare tactics on homeowners.

After the assessment, remediation must be done separately. In Roman's home, all equipment was isolated, and the house was brought under negative pressure with HEPA filtration. There was also surface cleaning and HEPA vacuuming. Then, after remediation, there is a post-remediation verification (PRV). The PRV is carried out by a mold assessor, not a remediator, and determines whether the remediator did their job (and in some states, like Florida, there are criminal penalties for referral payments between assessors and remediators). A PRV consists of IAQ tests and lab measurements, and the results should reveal lower numbers than the original assessment and the outdoor air.

Have a question that you want us to answer on the podcast? Submit your questions at https://www.speakpipe.com/hvacschool

Purchase your tickets or learn more about the 8th Annual HVACR Training Symposium at https://hvacrschool.com/symposium.

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400 CFM per ton is useful—until it isn't.

In this episode, Bryan and Ty take on one of the trade's favorite rules of thumb. It can be a reasonable starting point for many systems under moderate, near-sea-level conditions, but it is not a universal target. Proper airflow depends on actual delivered capacity, sensible and latent load, air density, climate, manufacturer data, and what the system is supposed to accomplish—not just the tonnage stamped on the cabinet.

They explain why dry-climate and high-altitude applications may require more volume airflow, why humid applications often use less coil airflow to improve moisture removal, and why mass flow matters more than volume alone. They also cover nominal versus actual capacity, suction-line pressure drop, equipment-specific performance at 208 V, Manual S and expanded performance data, and field verification with measureQuick and the TrueFlow® Grid.

The takeaway is simple: use the rule as scaffolding, then measure the system and follow the equipment data.

This episode contains embedded sponsor messages from Refrigeration Technologies, Carrier, NAVAC, and Filtrete.

Resources:

• Not All CFM Are Created Equal
• Impacts of Decreasing Evaporator Airflow
• Troubleshooting With DTD
• AHRI Data vs. Manufacturer Expanded Performance Data
• Bypass Dehumidification Airflow Design
• HVAC School calculators
• Submit a podcast question
• Learn about the GRIT Foundation

Purchase your tickets or learn more about the 8th Annual HVACR Training Symposium at https://hvacrschool.com/symposium.