HVAC School - For Techs, By Techs

In this episode, Bryan is joined by Matthew Taylor, a supermarket refrigeration specialist whose expertise centers on CO₂ rack systems, and Andrew Greaves, Director of User Experience at NAVAC Tools, for the third installment of their series on triple-point evacuation. The conversation expands beyond water to bring CO₂ into the picture, exploring where the two refrigerants behave similarly around the triple point and "more importantly" where the differences can create serious field problems. Whether you're pulling vacuums on residential equipment or servicing transcritical CO₂ racks at a grocery store, understanding what actually happens at these phase boundaries will change how you approach the work.
The triple point of water sits at 4,579 microns, corresponding to just above 32°F (273 Kelvin). Andrew shares a fascinating piece of metrology history: for decades, the Kelvin was formally defined as one two-hundred-and-seventy-third of the triple point of water, making it the most reproducible temperature constant ever established. In practical HVAC terms, this means that any time a technician hits industry-standard evacuation targets, they pass right through the triple point of water "every single time." The danger isn't the crossing itself but what happens when moisture is present in a cold ambient: the vacuum pump can create ice, and because sublimation requires enormous energy input from the surrounding environment, that ice can persist and deliver a falsely passing vacuum reading. Andrew explains why a decay test is the real proof of a dry system, since sublimating ice will continue to raise the micron reading after the pump is isolated. The conversation also covers how micron gauges actually work: they measure thermal conductivity, not pressure, which is why refrigerant vapor entrained in compressor oil can cause wild, erratic gauge behavior that mimics both moisture and a leak simultaneously.
For CO₂, the triple point arrives at roughly 70°F and 75 PSI "conditions that are easy to stumble into in the field." Matthew explains that in an operating transcritical CO₂ system, the triple point itself isn't the daily concern; the danger comes when a technician relieves pressure too quickly and liquid CO₂ flashes right through the triple point, instantly forming dry ice inside the lines and creating a hard plug. On the opposite end of the scale, CO₂ faces a critical point at just 87°F and 1,055 PSI, something that is essentially unreachable for most conventional refrigerants but is a routine operating reality in warm climates. Matthew walks through exactly what happens in a transcritical system: above the critical point, the CO₂ behaves as neither liquid nor vapor, the PT chart no longer applies, and a conventional condenser becomes a "gas cooler" that rejects heat but cannot condense the refrigerant. The refrigerant must be forced through a high-pressure valve to drop it back below the critical point, where it flashes instantly into liquid inside a flash tank. The episode also covers the "burping" behavior of CO₂ pop-off valves during high-ambient conditions, the dangers of isolating liquid CO₂, and how grocery stores have evolved from keeping spare CO₂ cylinders on hand to battery-powered fractional compressor systems that keep the flash tank subcritical through power outages.
The episode wraps up with takeaways that apply across both refrigerant worlds. Big hoses and fast pumps don't eliminate moisture problems; they can actually create a false-confidence scenario where ice forms, the system still pulls deep, and the technician believes the job is done. The decay test remains the only reliable proof of dryness, and nitrogen sweeps serve multiple purposes: adding turbulence to help release refrigerant from oil, displacing refrigerant from the micron gauge sensor, and temporarily raising the system back above the triple point so ice converts to liquid before being removed as vapor. The group also briefly touches on the emerging CO₂ carbon capture industry, where the triple point is used intentionally to separate and harvest CO₂ from industrial flue gases. The world of CO₂ service is growing fast, from niche grocery racks to mini-split-sized transcritical units, and the tooling needed to work on the high-pressure side hasn't fully caught up yet.
Topics Covered
Triple point of water: 4,579 microns / ~32°F / 273 Kelvin, and its historic role defining the Kelvin scale
Why technicians pass through the triple point of water during every standard evacuation
How ice forms during deep vacuum pulls and why sublimation is slow without adequate heat input
How micron gauges measure thermal conductivity, not pressure, and what causes erratic readings
Distinguishing moisture, refrigerant-in-oil, and actual leaks during a decay test
Triple point of CO₂: ~70°F / 75 PSI, and how dry ice forms when liquid CO₂ is vented through it
Why liquid CO₂ must never be isolated and the dangerous pressure implications if it is
The critical point of CO₂ at 87°F / 1,055 PSI and why transcritical operation is unavoidable in warm climates
How transcritical CO₂ systems work: gas coolers, high-pressure valves, and flash tanks
CO₂ system operating pressure ranges across the suction, liquid, and discharge sides
Pop-off valves and the "burping" phenomenon in transcritical CO₂ systems during high-ambient conditions
Grocery store power outage scenarios and battery-powered CO₂ subcooling solutions
The role of crankcase heaters when pulling a vacuum on systems with oil-logged refrigerant
Nitrogen sweeps: turbulence, sensor displacement, and temporary triple-point recovery
Heated nitrogen as an emerging technique for improving vacuum quality
CO₂ carbon capture: using the triple point industrially to harvest CO₂ from flue gases
The rapid growth of smaller transcritical CO₂ systems and the current gap in high-side service tooling
 
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.
Subscribe to our podcast on your iPhone or Android.
Subscribe to our YouTube channel.
Check out our handy calculators here or on the HVAC School Mobile App for Apple and Android.

In this short podcast episode, Bryan talks about considerations for washing commercial coils and water challenges techs might face. Despite being the topic of debate within the last several years, cleaning coils matters and will affect performance.
When washing coils, we use Refrigeration Technologies Viper cleaners (especially Venom Packs) when we actually need cleaners. No matter which cleaner you use (or if you don't), you want some pressure and a high flow rate when rinsing, but keep in mind that some pressure-washers may produce too much pressure and too little flow; the sweet spot is around 300 PSI, and microchannel coils require extra caution. 
In terms of commercial maintenance contracts, we often have a lot of coils to wash and may not have adequate water access for the job. We find that the best move is to ask the client to install plumbing infrastructure that allows for better water access. If they refuse, you can increase the labor charge due to extra hose setups, reduced pressure, etc. The client must also be able to provide safe access to the coils; do not write a proposal or carry out a maintenance procedure if techs cannot carry out the work safely. 
Strict chemical policies are important, too. Water-first approaches are best; if a water wash is sufficient, use just water and only escalate to chemicals if there is a clear need for a stronger cleaning. If you use chemical cleaners, use the proper dilution ratio; over-concentrated cleaners can damage coils. Chemicals also require more rinsing, and it's more economical to do as little rinsing as possible. Pre-rinsing, adding cleaner from bottom to top, letting the cleaner dwell, and rinsing off is the ideal sequence.
If you encounter water challenges on the ground, you can use a ground-based water trailer with a high-output, low-pressure washer attached. If the issue is on the roof, a battery-powered washer can help (like the Dewalt 20V MAX cordless power cleaner); they draw from vessels of water, like 5-gallon jerricans. Remove the casing if you need to (making sure the client pays for that additional labor), and rinse from the inside out.
 
Learn more about Refrigeration Technologies cleaners at https://www.refrigtech.com/. 
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.
Subscribe to our podcast on your iPhone or Android.
Subscribe to our YouTube channel.
Check out our handy calculators here or on the HVAC School Mobile App for Apple and Android.

Bryan opens this conversation with Ty Branaman, Head of Training at the GRIT Foundation, by digging into a question that anchors everything else in the episode: what is trades education actually for? Ty's answer is unambiguous — it's about people, not information. He describes his own struggle with traditional, reading-heavy instruction and explains how that personal experience shaped his teaching method, one built around making concepts visible, relevant, and hands-on. Bryan builds on the idea, arguing that education is too often treated as a simple transfer of information when it's really a deeply human exchange, a kind of gift passed from one person to another through real, physical, kinesthetic experience rather than passive reading or watching.
From there, the conversation turns to artificial intelligence, the central topic of the episode. Ty is careful to clarify that he isn't anti-AI; he uses it daily to clean up grammar, soften prickly emails, and refine images. His concern is specifically about AI replacing the human elements of teaching — the mentor a student looks up to, the instructor who visibly cares whether someone actually learns. Bryan adds a related warning about AI confidently producing false information, citing examples from law and HVAC alike, and introduces the idea of an "AI human sandwich," where human creativity starts the process, AI assists in the middle, and a human vets and rehumanizes whatever comes out the other end.
Much of the discussion circles back to Ty's long-standing frustration with PowerPoint-driven training, and how AI threatens to make that problem worse by adding a synthetic avatar to read slides aloud instead of fixing the underlying issue. He recounts being written up at a previous job for skipping a PowerPoint lecture to take students into the lab, and shares a favorite teaching memory from Kalos, where an instructor named Burt used the Socratic method to walk trainees through assembling Unistrut by hand. Stories like the blower-wheel, set-screw lesson — where students learn far more by struggling through a mistake than by hearing the right answer recited to them — reinforce the episode's larger argument: hands-on repetition simply cannot be replaced by slides or scripts.
The episode closes on the mission of the GRIT Foundation and the broader case for investing in human mentors rather than administrative shortcuts. Ty and Bryan talk about the cost and effort behind genuinely human-made training videos from creators like Craig Migliaccio and SkillCat, contrasting that investment with how easily AI could fake the same content for far less. Bryan shares a personal story about teaching basic electrical work in Haiti and the unforgettable reaction of an elderly student who lit up the moment her circuit worked, while Ty reflects on the mentors who shaped his own career. Both agree that AI can support trades education, but it can never substitute for a person who genuinely cares whether someone learns.
Topics Covered
Why trades education is fundamentally about people, not the transfer of information
Where AI genuinely helps: grammar and tone, reassembling ideas, image editing, and basic legal or HR research
The line Ty draws — using AI to assist a person is fine, using it to replace one is not
The risk of AI confidently presenting false information, and why everything still has to be fact-checked
Bryan's "AI human sandwich" framework for using the tool responsibly
Ty's long-running critique of PowerPoint-heavy training and how AI avatars make the problem worse
Classroom stories: getting written up for skipping a PowerPoint, the blower-wheel set-screw lesson, and Bert's Socratic-method exercise with Unistrut at Kalos
The GRIT Foundation's commitment to hands-on, mentor-led learning over app-based or AI-generated content
The human effort behind training videos from creators like Craig Migliaccio and SkillCat
Personal mentorship stories, including a memorable lesson in Haiti and the mentors who shaped both guests' careers

 
Learn more about the GRIT Foundation at https://www.thegritfoundation.com/. 
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.
Subscribe to our podcast on your iPhone or Android.
Subscribe to our YouTube channel.
Check out our handy calculators here or on the HVAC School Mobile App for Apple and Android.

In this short Q&A podcast episode, Bryan answers a question from Evan, a licensed mold assessment consultant, about system oversizing: What can be done when an HVAC system is oversized to control humidity and keep occupants comfortable?
The extent of the problem will depend on how badly the equipment is oversized, whether it has any turn-down or staging, and how the latent capacity is set up. To make the equipment work as best as it can, reducing the airflow to about 350 CFM per ton can help, as well as properly setting up dehumidification modes. The downside to slower airflow is a likely increase in cabinet and duct sweating.
In brand-new houses, it may be possible to swap the condenser (though it may be unlikely with the recent refrigerant change) and then drop airflow at the air handler. You can use AHRI's data to look for a possible match and then check the manufacturer's expanded performance data to verify whether a new condenser is a match. 
It's also possible to decouple the latent and sensible loads by installing a dehumidifier. However, completely decoupling the loads is not always practical, as a properly-sized HVAC system is the main source of dehumidification (and the dehumidifier fills in the gaps). Dehumidifiers need to be installed properly (with the supply ducted into the supply duct). 
Intentionally derating the equipment's cooling capacity, such as via reheat, will turn it into a better dehumidifier, but you're still adding sensible BTUs and need to be aware of the consequences of that, including higher power bills. You can use electric reheat, remove insulation, or remove shades from windows. Using a smaller compressor until the system can be replaced and downsized would achieve a similar effect but comes with other negative consequences.
Right-sizing equipment, load-matching, and managing air movement and heat transfer are ultimately the keys to preventing moisture problems.
 
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.
Subscribe to our podcast on your iPhone or Android.
Subscribe to our YouTube channel.
Check out our handy calculators here or on the HVAC School Mobile App for Apple and Android.

In this episode of the HVAC School Podcast, Bryan sits down with Kelsey Hei and Andy Fox from 3M Filtrete to pull back the curtain on what really goes into a quality air filter. Most homeowners — and even some contractors — think of air filters as simple screens that catch dust, but as this episode makes clear, modern filter technology is anything but simple. From proprietary nonwoven fiber structures to electrostatic charging that turns fibers into "magnets" for microscopic particles, the science behind a great air filter is both fascinating and critically important for equipment health and the air we breathe every day.
The conversation digs deep into why MERV 13 has become the gold standard recommendation from organizations like the EPA and CDC — especially in the wake of COVID-19 and worsening wildfire seasons across the country. While higher MERV ratings deliver better particle capture, they can also mean higher pressure drop, which strains HVAC equipment. This is where Filtrete's MPR 1900 filter stands out: it achieves MERV 13 performance while maintaining a pressure drop comparable to most MERV 8 filters — roughly half that of leading competitors. That balance between filtration efficiency and airflow resistance is something 3M has spent over 35 years engineering.
One of the most compelling segments focuses on real-world testing. Rather than relying solely on lab data, 3M runs extensive in-home studies — placing filters in dozens of homes during Minnesota winters, then retrieving and analyzing them to measure real-life efficiency and pressure drop. This commitment to real-world validation ensures Filtrete's claims hold up in the messy, variable conditions of actual homes, not just controlled lab environments. Bryan and the guests also discuss how overloaded or collapsed filters can cause serious equipment issues, including frozen coils and system shutdowns in extreme cases — underscoring why filter quality and regular replacement matter enormously.
The episode wraps with practical advice for contractors and homeowners alike: if you're installing a new system, push for a four- or five-inch filter slot to maximize surface area, lower ongoing pressure drop, and extend filter life. For existing one-inch slots, the MPR 1900 is the top pick. The Filtrete Smart App is also highlighted as a handy tool for setting filter change reminders and monitoring local air quality — making it easier than ever for consumers to stay on top of their indoor air health.
Topics Covered
·       3M Filtrete's history — 35+ years of indoor air quality innovation, owning the full manufacturing value chain from raw fiber to finished filter
·       The three pillars of air filter design — Efficiency, pressure drop, and air filter lifetime — and how they must be balanced
·       Nonwoven media explained — Why random fiber orientation captures particles more effectively than woven fabrics
·       Electrostatic charging technology — How fibers are engineered to attract and trap microscopic particles
·       Charge stability over time — Shelf life testing and real-world in-home studies to verify long-term performance
·       Why MERV 13 matters — EPA, CDC, and ASHRAE recommendations; effectiveness against bacteria, viruses, allergens, and wildfire smoke
·       Pressure drop and airflow — How high-resistance air filters strain equipment, raise energy bills, and can cause system failures
·       MPR 1900 spotlight — MERV 13 filtration at MERV 8 pressure drop, with publicly available data through the California Energy Commission
·       California Energy Commission database — Publicly available pressure drop and efficiency data on every filter sold in the U.S.
·       Pleats and surface area — Why having more pleats equals better dust-holding capacity and a longer filter life
·       Frame strength and bypass prevention — How structural integrity affects real-world performance over the filter's lifespan
·       MPR rating system explained — Microparticle Performance Rating: Filtrete's system focused on capturing the smallest, hardest-to-catch particles
·       Exceeding ASHRAE minimums — Filtrete's MERV 11, 12, and 13 filters all capture significantly more fine particles than the minimum standard requires
·       One-inch vs. four/five-inch filters — Why thicker filters are ideal for new installs and how to maximize one-inch slot performance
·       Energy consumption impact — How pressure drop affects fan wattage, system efficiency, and real annual utility costs
·       The Filtrete Smart App — Set filter change reminders at 30/60/90 days, store filter sizes, and get local air quality alerts
 
Learn more about Filtrete's air filters at filtrete.com or download the Filtrete Smart App on your Android or iOS smartphone. 
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.
Subscribe to our podcast on your iPhone or Android.
Subscribe to our YouTube channel.
Check out our handy calculators here or on the HVAC School Mobile App for Apple and Android.