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System and Duct Design April 10, 2025, 8:19 pm

April 10, 2025

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HVAC School – For Techs, By Techs

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Why VRF Compressors Die w/ Roman

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Why VRF Compressors Die w/ Roman

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.[...]

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56:52

Why VRF Compressors Die w/ Roman

byBryan Orr

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

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<strong>Nylog Blue Gasket -Thread Sealant for AC/R Systems</strong><br> One drop of Nylog on your rubber hose gaskets prior to attaching your core tools, hoses or vacuum gauge will assure that things do not bind or leak during evacuation. Derived from refrigeration grade lubricants. Non-hardening, non-drying fluid which bonds tenaciously to many different substrates. Typically, one drop of Nylog can be stretched about three feet before breaking.

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