Less Compressor, More Suction Pressure - Short #304

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. 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.

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.

In this short podcast episode, Bryan and Roman Baugh talk about indoor air quality and microbial control, specifically MERV 15 filter physics and how it all works when bringing in outdoor air. We filter indoor air to keep dust and particles off the equipment and keep them from circulating through the air. However, we also need to filter fresh air. While indoor air has several pollutants, including dust and VOCs, that make outdoor air dilution a sensible solution, outdoor air also has spores and other pollutants we want to filter out, and its quality can be hard to evaluate. Roman had an ERV that fed his VRF system, and it had significant microbial growth inside; he had some MERV 6 filtration on it, but that didn't capture particles effectively enough. MERV ratings measure the ability to filter particles out, and we use a unit called microns to measure particle size; higher ratings indicate a greater filter surface area and a better ability to filter out smaller particles. ASHRAE 52.2 divides particles into three categories: E1 (ultra-fine particles between 0.3 and 1 micron in diameter), E2 (fine particles between 1 and 3 microns), and E3 (coarse particles between 3 and 10 microns in diameter). MERV 15 filters have a 90% capture rate of E2 particles and a 90%+ capture rate of E3 particles. Fungal spores tend to fall in the E2 or E3 category, and filtration can keep those from coming into the home with fresh air; bringing in fresh air to dilute indoor pollutants is good, but we need a nuanced approach, and good filtration (without bypass) is part of that equation. Filters can also capture much smaller particles due to the way those particles move. Smaller particles move via Brownian motion, which makes them move erratically and more likely to collide with filter media. However, filter use and design, as well as fresh air intake location, can also affect filter efficacy. Filters that don't fit well in the slot enable bypass, and some filters might be restrictive. Exhaust ventilation outlets also play a role, as wind can bring those pollutants back to fresh air intakes.   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.