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Tech Tips:

Why the Breaker Size May Be Lower than the MCA (and Why That’s NOT Necessarily a Code Violation)

This HVAC system we recently installed has been causing quite a bit of trouble for us with inspectors. If you look at the label, you will see that the breaker size is 25 amps, and the minimum circuit ampacity (MCA or wire size) is 29 amps. The MOCP (maximum overcurrent protection, max fuse, or max […]

Why is the Breaker Tripping?

Breakers are designed to trip anytime the circuit draws a current above the rating for a period of time. The time the breaker takes to trip is a function of how high the circuit amperage is compared to the breaker rating. The higher the amperage above the rating, the faster the breaker will trip. Breakers […]

MCA is 27 and the Breaker is a 50A – Short #219

In this short podcast episode, Bryan and Mike from DITEK talk about what to do in tricky electrical scenarios, such as when the MCA is 27 and you have a 50A breaker. When you size an HVAC system for compatibility with voltage monitors, like the DITEK Kool Guard, you need to pay attention to […]

Anthony Perez
#breaker #circuit breaker #fuse

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HVAC School – For Techs, By Techs

Real training for HVAC ( Heating, Ventilation, Air Conditioning and Refrigeration) Technicians. Including recorded tech training, interviews, diagnostics and general conversations about the trade.

In this comprehensive episode of the HVAC School podcast, host Bryan Orr sits down with three experts from Copeland to demystify tandem and trio compressor systems. Joining him are Gina Kahle (Multiples Engineering Manager with 12+ years at Copeland), Tyler Daniels (Product Management team member), and James Stevenson (Technical Sales veteran with 28 years of field experience). Together, they provide both the engineering perspective and real-world service insights that technicians need to understand these increasingly common systems.

The conversation begins with the fundamentals: tandem and trio systems represent an evolution in compression modulation, allowing multiple compressors to work together on a single circuit rather than requiring separate circuits for each compressor. This design philosophy delivers significant advantages, including energy savings through better modulation, simplified system design, reduced costs, and the ability to meet stringent minimum modulation requirements (such as the 25% threshold for units under 60,000 BTUs per hour). The team emphasizes that tandems aren’t just about pairing any two compressors together—Copeland engineers carefully consider application requirements, flow characteristics, and stress testing to ensure reliable oil management and system resonance control.

A major focus of the discussion centers on practical service considerations that every technician needs to understand. James provides invaluable guidance on identifying whether a failed compressor in a tandem system can be replaced individually or requires replacing the entire tandem assembly. The “rule of thumb” is clear: compressors small enough to fit in residential systems (typically under 10 horsepower or about 7 inches in diameter) generally require full tandem replacement, while larger units may allow single compressor replacement. The distinction between “tandem ready” and non-tandem ready compressors becomes critical here—larger compressors (10+ horsepower) are typically sold tandem ready at wholesalers with the necessary oil equalization ports and sight glass connections, while smaller units are not.

The episode also explores advanced topics, including the integration of Enhanced Vapor Injection (EVI) technology with tandem systems, particularly for cold climate heat pump applications. Gina explains how EVI extends the operating envelope down to -40°F, opening new markets and applications. The team discusses the transition to A2L refrigerants and how Copeland continues to innovate despite changing regulatory landscapes. Throughout the conversation, they emphasize the critical importance of proper oil management through oil equalization lines (OEL) and two-phase transfer lines (TPTL), and why maintaining these connections exactly as designed is non-negotiable for system longevity.

Key Topics Covered:

Tandem and Trio Basics: Definition and benefits, including energy savings, cost reduction, and design simplification
Modulation Requirements: Meeting state-mandated minimum modulation thresholds (25% for units under 60,000 BTU/hr)
Applications: Data centers, DOAS units, rooftops, chillers, and various commercial spaces
Compressor Pairing Options: Fixed speed, digital, variable speed, two-stage, and mixed configurations
Oil Management: Critical importance of oil equalization lines (OEL), two-phase transfer lines (TPTL), and gas equalization lines (GEL)
Service and Replacement: How to identify tandem-ready vs. non-tandem-ready compressors; when to replace individual compressors vs. full tandem assemblies
Visual Identification: Using compressor size (7″ vs 9″ diameter), port configuration, and horsepower ratings to determine replacement strategy
Piping Configurations: Three-pipe vs. four-pipe designs and when each is necessary
Installation Considerations: Importance of keeping oil equalization lines level (parallel to ground) and using proper mounting spacers
Enhanced Vapor Injection (EVI): How EVI technology extends operating envelopes to -40°F for cold climate heat pump applications
Energy Efficiency Standards: Meeting IEER, IPLV, and upcoming IVEC standards through strategic tandem use
Copeland Mobile App: Features, including parts lookup, resistance specifications, amperage mapping, AI Scout assistant, and technical bulletins

Learn about the Copeland Mobile app at https://www.copeland.com/en-us/tools-resources/mobile-apps/copeland-mobile.

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 7th Annual HVACR Training Symposium at https://hvacrschool.com/symposium.

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Check out our handy calculators here or on the HVAC School Mobile App for Apple and Android.

Search Episodes

Are Two Are Better Than One: Understanding Tandem Compressors

12/04/2025

Bryan Orr

The Tech That Tried to Beat the Compressor – Short #268

12/02/2025