HVAC School - For Techs, By Techs

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
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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.