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Oil Return and Refrigerant Charge in VRV w/ Roman Baugh

By Roman Baugh Bryan Orr

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Roman Baugh joins the podcast to talk about oil return and the refrigerant charge in VRV systems.

VRV systems—also known as variable refrigerant volume (or variable refrigerant flow/VRF) systems—have one outdoor unit, one or multiple compressors, and multiple indoor units. The outdoor unit modulates to meet the indoor units’ fluctuating demands. They are versatile and flexible systems.

Like parallel racks, VRV systems have long lines and a lot of piping, so oil return and refrigerant charge are especially critical. VRVs have specific control protocols, as they need refrigerant volume and velocity to move oil and keep it lubricating the compressor for its entire lifespan; oil return mode, the refrigerant charge, and the piping protocols are supposed to support that function.

When it comes to piping protocols, line sizing is critical. Whenever there is a need to relocate the outdoor unit and change the piping configuration, the charge needs to be adjusted, and the piping may even need to be upsized to prevent restrictions from happening. Daikin has VRV WebXpress (and SplitXpress) software for equipment selection; the goal is to help installers out with the line length and charging whenever it needs to be changed.

When trying to get the oil return and line sizing right, you ultimately need to look at the manufacturer’s literature and resources. It also helps service technicians if the installer makes the charge and line information readily available to anyone who works on their VRV install in the future.

Roman and Bryan also discuss:

Where and how oil can settle in VRVs
Consequences of improper charge in VRVs
Liquid lines in VRVs
Violating piping rules and safety protocols
Vertical separation in liquid line sizing
Suction line sizing
POE and PVE oil miscibility
Daikin’s resources

Check out daikincity.com to find Daikin’s literature and software programs.

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Author:

Roman Baugh

Company: Kalos Services

Position: Director of Commercial HVAC

Bryan Orr

Company: Kalos Services

Position: Co-Founder and President

Check out our most recent video

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Our latest Podcast

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 live stream, co-branded with Kalos, Bryan Orr sits down with Kalos refrigeration team members Christian Maitland and Alex Orr to talk about the realities of working on market refrigeration systems. The conversation starts with the rapid arrival of new equipment in grocery stores, especially transcritical CO2 racks, and why even well-trained techs are running into problems nobody has seen before. Because these are engineered, built-up systems rather than mass-produced units, the first real stress test often happens in the field, during installation and startup.

The group digs into where those problems actually come from. Some are classic installation errors, like skipping nitrogen purges while brazing, leaving burrs in pipe, or forgetting that ACR copper plugs sit on the inside of the pipe. Others trace back to the manufacturer: sensors landed on the wrong terminals, swapped sensors that left a condenser fan unable to run, controllers that overheat and reset, and programming that was tested in a different climate than the one the equipment ends up in. With multiple manufacturers supplying the rack, controller, and condenser, nobody owns the interface between the pieces, so startup techs end up tuning parameters store by store.

Bryan, Christian, and Alex also walk through the root cause process they rely on, which is essentially the scientific method: observe the complaint, form a hypothesis, test it, and then keep digging until you know why it happened and can confirm the fix on the next job. They discuss store dew point and airflow as the most common causes of iced-up and sweating cases, a humbling misdiagnosis involving a transducer and a redundant controller, and the pain of 19-week lead times and wrong parts arriving seven times in a row.

The episode closes with practical advice for techs. Walk into every store and use your senses, check behind your install team, pull your vacuums, and document conversations with customers when expectations don’t match the equipment specs. Christian encourages techs to share what they learn with peers, Alex reminds listeners that solving ridiculous problems is the job and a chance to be the hero, and Chad’s late addition is a reminder that equipment should be designed for worst-case conditions rather than a design day.

Topics Covered

Transcritical CO2 coming to the U.S. market, and why it behaves differently above roughly 86°F
Challenges of high ambient temperature and humidity in Florida, including limits of adiabatic cooling
Controllers that overheat and reset, and how quickly a CO2 system can lose its charge when that happens
Safety and mindset for techs moving from traditional DX to high-pressure CO2 systems
Why built-up systems get their first real field test at installation and startup
Clean piping practices: nitrogen purging, burrs, carbon buildup, and tiny orifices in ejectors and microchannel coils
The pipe plug in the EPR story and other lessons from early grocery work
Manufacturer errors caught at startup, including miswired harnesses and swapped sensors
Interconnected controls from different manufacturers and the need for site-specific programming
Setting customer expectations on case placement, shelving, and spec limits, and documenting those conversations
Store dew point, dehumidifiers, and ceiling fans disrupting open-case air curtains
Using building science tools like smoke pens and vane anemometers on refrigeration cases
The root cause process: observe, hypothesize, test, find the real cause, and verify the fix
A transducer misdiagnosis and why to rule out everything before ordering long-lead-time parts
Parts lead times, wrong parts, and the hidden labor cost of learning new equipment alongside manufacturers
Commissioning during live-store case swaps, and the gap in manufacturer training for new equipment
What techs look for on a first walkthrough, plus startup checks like line sizing, case assembly, and pulling vacuums
Gaps in tools, such as digital gauges built for transcritical systems
Closing takeaways: share knowledge with peers, own the problem, and design equipment for worst-case conditions