HVAC School - For Techs, By Techs

In this short episode from the Bry-X stage of the 7th Annual HVACR Training Symposium, Tessa Murry gives a class on building science basics: The House Always Wins! Tessa is a building scientist who works with TEC.
Tessa's class is about how the house puts HVAC contractors in difficult situations. When people have indoor air quality or comfort concerns, the HVAC often takes the blame, even if the issue is with the house. There are usually several little home improvement decisions that create unintended consequences and add up. In many cases, when there aren't exhaust fans in kitchens and bathrooms, moisture stays inside and can cause indoor condensation. Air-sealing, adding or removing insulation, replacing windows, replacing furnaces with a different efficiency model, and even moving people in can all affect comfort and air quality.
Comfort issues and complaints, such as hot and cold spots, often point to issues with the house, not necessarily just the HVAC system. Pressure boundaries and thermal boundaries in the building envelope need to be aligned, continuous, and consistent for HVAC systems to do their job well, but many houses don't have that. Those boundaries need to be clear between attached spaces like attics or garages. Those spaces create problems with energy efficiency and comfort, and humidity is a problem in some climates. Garages also have fumes we want to keep out of the house. 
Heat moves from hot to cold, and air moves when there is a pressure differential. Mechanical equipment and wind can drive pressure differentials. If there is a pressure difference and a hole, there will be air movement. In the winter, cold air sinks and displaces warm air, which rises and creates positive pressure at the top of the house. That air will push through gaps around can lights, vents, and more. When that humid air gets into a cold attic, the moisture will condense on the roof decking surface and cause an ice dam to form. In the summer, hot, humid air comes into the structure. Regardless of the house's issues with air movement, it's on HVAC contractors to make the decisions that put the occupant's health and safety first, including calling the contractors with the knowledge to diagnose the house's problem.
 
Have a question that you want us to answer on the podcast? Submit your questions at https://www.speakpipe.com/hvacschool.
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In this episode, Bryan sits down with compressor teardown specialist Ty Branaman for a deep dive into what really kills refrigeration and AC compressors. After some lighthearted banter, the conversation quickly turns technical: Ty has spent years cutting apart failed compressors on video, and he explains why that practice matters so much. As he puts it, he is "all about making the invisible visible" — once a technician actually sees what happened inside a dead compressor, vague explanations like "it just got old" stop holding up.
Bryan and Ty establish that a properly maintained compressor should essentially last forever, since it is a sealed system with no external contaminants — unlike an engine. The catch is that installation and service mistakes introduce the very contaminants that shorten its life. Copper plating tops Ty's list of the most common findings: moisture combines with POE oil to form acid, which etches copper that then plates onto moving parts, thickening them and eventually causing hard starts that get mistaken for a "tired" compressor. They also trace how a shorted or seized compressor is usually the end result of an earlier root cause, not the cause itself.
The two work through the major categories of contamination one by one: solid debris from unswept lines and copper shavings left behind during deburring; moisture, which requires a proper pressure test, deep vacuum, and decay test to remove, plus heat to actually drive water molecules out; and non-condensable gases like oxygen and nitrogen, which throw off pressure readings and, with flammable A2L refrigerants, introduce real fire risk. Ty shares a memorable story about a compressor shell that ripped open after being left pressurized with nitrogen, and both discuss the surprisingly common problem of "wet" nitrogen and poorly maintained recovery tanks.
The conversation closes on flooded starts — a hazard Ty considers hugely overlooked — where migrated liquid refrigerant mixes with crankcase oil and violently flashes to vapor on startup, often shattering scroll plates. They cover practical prevention methods, including crankcase heaters, pump-down solenoids placed ahead of the metering device, and reduced refrigerant charges, before wrapping up with Ty's quick field technique for cutting the top off a failed compressor to get an on-the-spot diagnosis rather than waiting on a full teardown back at the shop.
Topics Covered
Why compressors fail from external contamination rather than simply "wearing out"
Copper plating as the most frequently found problem inside failed compressors
Solid contaminants: dirt, copper shavings, and proper deburring technique
Moisture control: pressure testing, deep vacuum, decay testing, and heat-assisted evacuation
Wet nitrogen and poorly maintained recovery tanks
Oxygen and nitrogen contamination, including flammability risks with A2L refrigerants
Flooded starts, crankcase heaters, and pump-down solenoids
Superheat measured at the compressor versus at the evaporator outlet
Ty's quick-cut technique for on-the-spot compressor diagnosis in the field
 
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.
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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 multi-position service valves and more valve types.
Many typical residential systems have brass service valves with a hex cap and Schrader ports; access happens solely through the Schrader ports (where the cores are). Schraders are restrictive and prone to leaking, and they don't have the ability to back-seat or front-seat. In applications where we need that capability, we use multi-position service valves instead. (Note: CoreMax valves have much higher flow rates, but you can't remove the cores except with a highly specialized tool.)
Multi-position service valves are common in commercial refrigeration and allow for unrestricted, full-port flow. They do not have spring-loaded cores in the service port. If you treat these valves like Schrader valves, refrigerant WILL come out if it's not back-seated. You adjust the position by turning the stem with a refrigeration service wrench; loosen the packing nut before attempting to turn the stem, as tightening it down will crush the compressible packing material around the rotating stem. Tighten it back down after making your adjustment.
These valves also require lots of heat to braze, so we must cover heat-sensitive surfaces with wet rags or heat-blocking putty (like WetRag by Refrigeration Technologies). The valve must be mid-seated while brazing, not fully front-seated or back-seated, as the surfaces are more likely to warp otherwise. Mid-seating the valve also provides a high-volume path directly to the system. Back-seating the valve is the everyday running position (stem must be rotated fully counterclockwise) and blocks access to the service port. Cracking off the back seat requires you to rotate the stem slightly clockwise with service hoses securely attached, just enough to allow you to get a reading through a tiny gap. Front-seating the valve is good for isolation with the compressor off but may cause compressor failure or serious injuries if you run the compressor. Front-seating requires you to rotate the stem fully clockwise; it completely blocks the flow of refrigerant through the system, and the service port stays open to the upstream side of the valve body. Catastrophic compressor failure will happen if the suction or discharge valves are front-seated while running.
General multi-position service valves are NOT king valves. King valves are multi-position service valves specifically located at the outlet of the liquid receiver. These valves front-seat to help you pump down the system when you need to do repairs on the low side; it blocks liquid refrigerant from leaving the tank. A queen valve may be located at the inlet of the receiver on the drop leg from the condenser; front-seating it with the king valve will fully isolate the receiver.
 
Multi-position service valve tech tip: https://www.hvacrschool.com/compressor-multi-position-service-valves/ 
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.
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Check out our handy calculators here or on the HVAC School Mobile App for Apple and Android.

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.