In this episode, Bryan and Roman dive deep into the world of Variable Refrigerant Flow (VRF) systems, focusing on the persistent issue of compressor failures. VRF technology has evolved, and it has seen a major rise in the North American market since the early 2010s. Roman shares his passion for VRF, tracing its origins back to 1982 and explaining how it earned the nickname “chiller killer” by replacing traditional chiller systems in large facilities like hotels, churches, and schools. However, with this rapid adoption came a troubling reputation: VRF systems became notorious for frequent compressor failures, prompting some institutions to revert to older technologies.

There are three primary causes of compressor failure in VRF systems: oil lubrication issues, liquid refrigerant return, and electrical failures. VRF compressors are shipped with excess oil to account for the system’s extensive piping and multiple indoor units, but improper refrigerant charge—either overcharging or undercharging—can disrupt oil return and lead to gradual compressor death. They emphasize the importance of correct installation, accurate charge calculation, and diligent maintenance. Bryan adds that measuring discharge superheat is a key diagnostic tool: high discharge superheat with normal suction superheat signals poor lubrication and impending failure.

The discussion then shifts to the dangers of liquid refrigerant returning to the compressor. Even small amounts can wash oil off the scroll plates, leading to metal-on-metal contact, galling, and eventual mechanical breakdown. Roman details the difference between high-pressure shell and low-pressure shell compressors, noting that VRF systems are more susceptible to operational flood back, which can cause elevated amp draws and catastrophic failure. They also highlight the role of contamination—such as copper shavings or sand from installation—which can damage expansion valves and lead to chronic flood back issues. Maintenance, including regular oil analysis and monitoring of expansion valve performance, is crucial for long-term reliability.

Finally, the episode covers electrical failures, often the result of underlying mechanical issues rather than true electrical faults. The hosts advocate for using insulation resistance testing (megohmmeters) as a maintenance tool to track winding degradation over time. They stress that proper cleanup after a compressor failure is vital, recommending temporary filter dryers and oil analysis to mitigate contamination. The conversation closes with practical advice: always investigate the root cause of a compressor failure, communicate findings with clients, and prioritize best practices in installation and service to prevent repeat issues. 

Topics Covered in This Episode:

• The history and rise of VRF technology in North America

• Why VRF systems earned the nickname “chiller killer”

• The three primary causes of VRF compressor failure:

  • Oil lubrication issues (overcharge/undercharge, oil return)

  • Liquid refrigerant return (flood back, expansion valve failures)

  • Electrical failures (mechanical causes, insulation degradation)

• Diagnostic techniques: discharge superheat, suction superheat, amp draw analysis

• The impact of installation practices and system contamination

• Maintenance best practices: oil analysis, filter dryers, insulation resistance testing

• The importance of root cause analysis after compressor failures

• Resources for ongoing VRF education: VRF Tech Talk podcast, Facebook group, and Roman’s YouTube channel

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 6th Annual HVACR Training Symposium at https://hvacrschool.com/symposium.

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In this short podcast episode, Bryan talks about some no-serve situations he's encountered as a technician and HVAC business owner. He also talks about situations that may be unpleasant but aren't quite no-serve situations.

Some common and obvious no-serve situations are when a client threatens a technician, especially with lawsuits, bad reviews, or even bodily harm. However, some clients are just naturally defensive, so we want to be careful and give people a chance if they're angry and might just need to calm down.

Unrealistic expectations can also cause no-serve situations. Some complaints are tricky to deal with but can be solved, but other problems are impossible to solve. We have every right not to serve clients who have problems that don't have realistic solutions (such as wanting a thermostat that doesn't make a clicking noise at all). In those cases, Kalos usually gives some degree of a refund and agrees not to do business with the customer again.

Dirtiness of the living space can also be a no-serve situation. Unless a home is dangerously filthy (e.g., it can cause a respiratory disease) or the equipment is not accessible, we can serve them. Even if the home is filthy or the equipment is inaccessible, we can ask the owner to clean up and return to serve them. On the other side of the coin, hypochondriacs can be a challenge to deal with, but no-serve situations are rare; we can take precautions, including more thorough testing and hold-harmless agreements.

Other no-serve situations are people who don't pay, people who regularly pay extremely late, customers who aren't the owner (such as tenants or family members), and clients who try to drag you into drama with other contractors.

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 6th Annual HVACR Training Symposium at https://hvacrschool.com/symposium.

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In this informative HVAC podcast episode, Bryan and Bert dive deep into the complex world of locked and internal overload compressors, focusing specifically on single-phase residential units. The discussion begins with Bert explaining one of the most common challenges technicians face: diagnosing a locked compressor. He describes how compressors that are locked will typically run for only a second before overheating and stopping, creating a cycle that can be difficult to detect if technicians aren't carefully monitoring at the right moment.

The hosts share personal experiences and practical diagnostic techniques, with Bert recounting how he once simulated a locked compressor by cutting the start winding wire and concealing it beneath other wires and zip ties. This demonstration highlights the importance of thorough inspection, including checking terminal connections. Bryan shares a story from his early career when he mistakenly condemned a compressor with damaged terminals, not knowing about terminal repair kits - a candid moment that illustrates how even experienced technicians continue to learn throughout their careers.

A significant portion of the podcast is dedicated to explaining the electrical fundamentals of compressor operation, including an enlightening discussion about start windings, run windings, and common connections. Bryan passionately clarifies misconceptions about current flow through these different windings, explaining that the start winding actually has consistently lower amperage due to its connection through a capacitor. The hosts also detail the critical differences between a compressor that's overheating versus one that's truly locked, emphasizing that the physical temperature of the compressor often provides the key diagnostic clue.

Key Topics Covered:

·        How to identify a locked compressor versus one that's out on internal overload

·        The importance of checking terminal connections and wire continuity

·        Why compressors that are truly locked don't have time to physically overheat

·        Common causes of compressor overheating: condenser fan failure, refrigerant issues, airflow problems

·        The proper diagnostic method for catching a locked compressor "in the act"

·        The mechanics of start windings versus run windings and their amperage differences

·        When and how to use hard start kits appropriately (and why they shouldn't be used universally)

·        How to communicate with customers when diagnosing compressor issues

·        The role of crankcase heaters in preventing flooded starts

·        Terminal repair techniques and when they're appropriate

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 6th Annual HVACR Training Symposium at https://hvacrschool.com/symposium.

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In this short podcast episode, Bryan covers some unique electrical cases: when 0v isn't safe.

When you measure voltage, you're finding out the electrical potential between two points. Just because there is 0v between one point and another doesn't mean there will be 0v between those points and other points. Non-contact voltage detectors are good tools that measure the flux from the wiring, but they have their limitations.

A common mistake is measuring voltage across a switch. When you measure 0v across the switch, that could mean there is 0 potential to ground, neutral, or the other leg, but it could also represent a closed switch where power is actively being passed. You need to measure voltage across a load or with neutral as the other point.

You will also measure 0v when one of the legs of 240v power (with a two-pole breaker) stops making contact. You'll measure 0v between the legs, but that's because one of the legs is open. There may still be a complete path on the other leg; therefore, you will want to check for voltage between each leg and ground, not leg to leg. This condition is particularly common in pool heaters.

In some cases, the meter isn't working and will read 0 when it's set to another unit setting, isn't on (if an analog), or the leads aren't fully plugged in. Check to make sure your meter is on the correct setting, is in proper working order, and has a good connection to the leads.

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 6th Annual HVACR Training Symposium at https://hvacrschool.com/symposium.

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In this episode, Bryan and Bert dive into the often misunderstood world of compressor testing, focusing on common mistakes technicians make when using ohmmeters, compressor testers, and megohm meters. The conversation highlights how diagnostic errors can lead to unnecessarily condemned compressors and wasted time and resources.

The hosts begin by discussing fundamental concepts like the difference between "open" and "short" conditions, emphasizing that a path doesn't necessarily indicate a short circuit—it simply means there's a low-resistance path. They explore how many technicians get confused when testing terminals, mistakenly thinking that normal winding-to-winding measurements indicate a problem. Through practical examples from their field experience, they illustrate why understanding normal readings is crucial before taking any measurement.

A significant portion of the discussion centers on proper testing techniques for scroll compressors, which often show different measurements to ground compared to other compressor types due to their design, with windings submerged in refrigerant and oil. Bryan and Bert explain why standard motor testers can lead to false diagnoses when they indicate "bad" at threshold levels like 20 megohms—a reading that would be normal for many functional scroll compressors. They recommend proper megohm meters calibrated to appropriate voltage levels for accurate testing.

Key Topics Covered:

• The difference between "open" circuits and "shorts" and how to properly interpret ohm readings
• Common mistakes when testing compressor terminals, especially misinterpreting normal winding-to-winding measurements
• How to properly check for shorts to ground and the importance of clean connections
• Why scroll compressors naturally show different resistance-to-ground readings due to their design with submerged windings
• Problems with inexpensive compressor testers that give false "bad" readings on functional equipment
• The "redneck test" for isolating a compressor to determine if it's truly the source of breaker trips
• The importance of understanding meter auto-ranging and correctly interpreting readings in ohms, kilohms, and megohms
• Why a reading below 0.5 megohms to ground is the general threshold for concern with scroll compressors
• Differences between megohm meters, high pot testers, and standard multimeters
• The misconception that winding-to-winding shorts are common without corresponding shorts to ground

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 6th Annual HVACR Training Symposium at https://hvacrschool.com/symposium.

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In this short podcast episode, Bryan talks about what the ambient rating means on a motor. These ratings can be found on both condensing fan motors and blower motors. They have Cs in their rating, which represents the maximum ambient temperature the motor can handle in degrees Celsius (like 40C or 60C).

Heat and overvoltage kill motors, and motors with higher ratings can withstand higher temperatures and last longer in hot conditions. Be careful not to confuse this rating with the insulation class (which is classed by letters and corresponds to temperature limits). You could have a condition where you exceed the insulation's rating but not the ambient rating. 

Air over operations (especially in the case of TEAO motors - totally enclosed air over motors) also play a role. The airflow helps cool the motor, and airflow restrictions like dirt and soil can create conditions that cause the motor to exceed its rating. 

Motor bearings also matter. Ball bearings tend to last longer and withstand higher temperatures than sleeve bearings, but they are noisier. Many motors use sleeve bearings, and replacing a sleeve bearing motor with a motor that uses ball bearings may negatively affect the homeowner's comfort due to the noise, so that's a conversation you'll want to have with the customer and set realistic expectations.

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 6th Annual HVACR Training Symposium at https://hvacrschool.com/symposium.

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In this episode of the HVAC School podcast, host Bryan discusses superheat with guest JD, who recently co-authored an article on the topic with Ty Branaman. The conversation explores the often misunderstood concept of superheat, its importance in HVAC diagnostics, and common misconceptions technicians have when measuring and interpreting it.

Bryan begins by sharing how superheat was initially taught to technicians in the late 1990s and early 2000s, primarily as a method for charging fixed metering device systems. He explains how this limited view led to problems, as technicians would often add or remove refrigerant based solely on superheat readings without considering other system factors or giving the system time to stabilize. JD points out how the industry shifted when TXVs (Thermostatic Expansion Valves) became standard, with many technicians abandoning superheat measurements altogether in favor of subcooling measurements, missing crucial diagnostic information in the process.

The discussion then evolves into a more sophisticated understanding of superheat as an indicator of evaporator coil "fullness." Bryan explains that lower superheat indicates a fuller evaporator coil, while higher superheat suggests a starved coil. They discuss the importance of measuring superheat in the correct location, noting that TXVs control superheat at the evaporator outlet, not at the condensing unit where technicians often measure. This misunderstanding leads to many incorrect diagnoses of "bad TXVs" when the real issues might be related to airflow, heat pickup in line sets, or other factors. Both experts emphasize the value of measuring superheat both inside at the evaporator outlet and outside at the condensing unit to get a complete picture of system operation.

Key Topics Covered:

• Definition of superheat and its importance in HVAC diagnostics
• How superheat indicates evaporator coil "fullness" (flooded vs. starved conditions)
• The distinction between charging by superheat and using superheat as a diagnostic tool
• Common misconceptions about superheat measurement on TXV systems
• Why measuring superheat location matters (evaporator outlet vs. condensing unit)
• How to properly diagnose TXV issues using superheat measurements
• The relationship between airflow problems and superheat readings
• Normal superheat ranges for residential systems (7-14 degrees at evaporator outlet)
• How superheat affects both system capacity and compressor safety
• "Exercising" TXVs as a troubleshooting technique
• How line set conditions and installation factors can impact superheat readings
• System behavior during "hot pull down" conditions when starting with high indoor temperatures

JD and Ty's superheat tech tip and worksheet: https://hvacrschool.com/solving-superheat/ 

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 6th Annual HVACR Training Symposium at https://hvacrschool.com/symposium.

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In this short podcast, Bryan talks about how to deal with too much at work and in life. He gives some practical tips to help you when you feel overwhelmed.

One of the best ways to get ahead is to wake up early, exercise, get sunlight, stay hydrated, eat healthy, and get enough sleep. Taking care of yourself and giving yourself ample opportunities to set your mind and body up for success can ensure that you have the energy to tackle the challenges at work and in other areas of your life.

When you're in the middle of an overwhelming mix of tasks, it helps to take a small break and take some deep breaths. Some people take smoke breaks. Once you have an opportunity to step back and clear your head, try to document all of the things you need to do. You can use a Google Doc with the help of ChatGPT to lay everything out. Once you have all of your tasks in front of you, pick 3-5 things that must get done today and then use your calendar, silence your notifications, and use all the tools at your disposal to focus on those things.

Perfectionism and people-pleasing can also get in the way of achieving all of your tasks. You have to be able to accept work that isn't perfect and say no to meetings or unnecessary tasks. You can use tools like Loom to document quick notes instead of holding a meeting. When you can't avoid meetings, try to batch them all at once. Batching, delegating, and automating tasks also come in handy, especially before tasks pile up and spiral out of control.

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 6th Annual HVACR Training Symposium at https://hvacrschool.com/symposium.

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Bryan from HVAC School interviews JD Kelly, known as "student of HVAC" on Instagram, about Delta T measurements in HVAC systems. This episode dives into the fundamentals of Delta T, common misconceptions, and proper measurement techniques.

JD explains that Delta T is simply a temperature difference between two points of the same medium, which is often misunderstood in the industry. Many technicians are taught to measure between return grills and supply registers, but this approach can lead to inaccurate readings due to external factors like duct leakage or heat gain from attics. The proper measurement should be taken directly at the equipment to evaluate how the evaporator coil is performing.

Humidity plays a significant role in Delta T measurements, which JD discovered when researching the fundamentals. Bryan elaborates on this point, explaining that in high-humidity environments (like Florida), more energy goes toward removing moisture (latent heat) rather than cooling the air (sensible heat), resulting in lower Delta T readings. This is why a newly repaired unit in a humid house might initially show lower readings but improve as the home dries out. The discussion highlights why the common "20-degree Delta T" rule of thumb isn't universally applicable and requires context.

Key Topics Covered:

• Definition of Delta T: Temperature difference between two points of the same medium
• Difference between Delta T and TD (temperature difference)
• Proper probe placement for accurate Delta T readings
• Impact of humidity on Delta T measurements
• How regional differences affect expected Delta T values
• Relationship between CFM (airflow) per ton and Delta T readings
• Common mistakes: Adjusting equipment based solely on Delta T readings
• Challenges of applying Delta T in heat pump heating mode
• How temperature dead spots can affect readings
• Why Delta T readings must be considered alongside other diagnostic tests
• The danger of making unnecessary adjustments to HVAC systems
• Why high Delta T isn't always good and low Delta T isn't always bad

JD's Delta T tech tip: https://hvacrschool.com/solving-delta-t/ 

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 6th Annual HVACR Training Symposium at https://hvacrschool.com/symposium.

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In this short podcast episode, Bryan talks about fire sprinklers and how to avoid setting them off on job sites.

Fire sprinklers have an element in the center that expands when exposed to heat (like a TXV sensing bulb) and breaks the glass. When the glass breaks, the fire sprinkler starts pouring out water. In some cases, fire sprinklers are linked to a larger fire suppression system in which several may go off at once, but most of the time, only a single fire sprinkler will go off if bumped or exposed to heat.

If you're using torches or doing any form of hot work in a closet or other location with a fire sprinkler, make sure to keep torches away from the heat-sensitive bulb or at least cover the sprinkler with a wet rag (and follow your company's guidelines). Blunt force is another possible issue, so we want to avoid hitting the sprinklers with lifts, ladders, or building materials like studs. Keep clearances in mind, and watch out for your colleagues.

You can get some specialty-built cages to protect the sprinklers, but awareness is one of the best ways to protect fire sprinklers. If possible, make sure signage is posted or that you alert other people in the area about the fire sprinklers.

If the fire sprinkler does go off, make sure you can quickly reach the person(s) who can access the fire shutoff or direct you to the fire shutoff. While fire sprinklers won't pose much of a personal safety hazard, property damage is a major concern. Training and awareness are the keys to preventing property damage due to fire sprinklers.

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 6th 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