How much R-11 vapor remains at 0 psig in a 350-ton chiller?

Why a 350-ton chiller at 0 psig still has vapor in it—and why it matters

If you work with large air conditioning or refrigeration systems, you’ve probably learned that every system is a story of two phases: liquid and vapor. The way these phases share space inside a charged system tells you a lot about how the system behaves, how you should service it, and what safety steps to take. Here’s a scenario that almost sounds too simple to be true, but it’s packed with practical insight: a 350-ton R-11 chiller, pressure at 0 psig, and the question of how much vapor remains after all liquid is removed.

Let me set the stage without turning this into a long wind-up. In a chiller, you have refrigerant circulating through a closed loop. Some of it is liquid, some is vapor, and some is a mixture. When you remove all the liquid, what’s left is vapor that’s trapped in the system’s pockets, tubing, or compressor suction lines. The exact amount depends on the refrigerant, the design of the system, and the pressure-temperature relationship of the refrigerant at that moment. For R-11, at 0 psig, the vapor is cold, yes, but it still exists as vapor and occupies a certain volume. The practical takeaway isn’t just the number; it’s knowing that you’ll always have some vapor left behind as the liquid is emptied.

Why the answer lands on about 100 pounds of vapor

In the multiple-choice style question you’ll see around EPA 608 topics, the correct option—about 100 pounds of vapor—reflects real-world behavior for a system of this size and refrigerant type. Here’s the intuitive logic:

• System charge and geometry matter. A 350-ton chiller represents a substantial amount of refrigerant charge. When you remove the liquid portion, you’re not magically removing all the mass. The remaining gas mass is tied to how much refrigerant was originally charged and how it distributes between liquid and vapor at the operating pressure and temperature.

• The 0 psig condition tunes the temperature of the vapor. At near vacuum pressures, the saturated temperature for R-11 is low. The vapor is still dense enough to carry a meaningful mass, especially in a large, purpose-built chiller where volumes are sizeable.

• The R-11 properties guide the estimate. Refrigerant R-11 has a known pressure-temperature relationship. At 0 psig, the vapor phase can hold a lot of mass in the system’s residual pockets, pipes, and components before you consider any fresh compression or recharging work.

A practical way to think about this is to imagine your system as a bottle with two phases inside. If you remove all the liquid, you’re left with gas that’s trapped in the headspace and cavity volumes. In a big machine like a 350-ton chiller, that headspace isn’t tiny. You don’t get a few ounces of vapor; you get a significant chunk, often around a hundred pounds, depending on the exact charge and how the refrigerant has settled in the hardware over time.

What this means for technicians and the EPA 608 context

• Safety first. Handling refrigerants, especially older ones like R-11 (which has environmental cautions tied to it), requires awareness of the vapor’s presence even when the system seems “mostly empty.” At 0 psig, the vapor can be cold enough to condense moisture in the air, but it’s still a gas. Don’t assume zero mass means zero risk.

• Measurement matters. When you’re diagnosing or servicing, don’t rely on “feels like” estimates. Use the correct gauges or weigh the system to determine how much liquid and how much vapor remain. Understanding the split helps you plan recovery, recycling, or reclamation steps in line with environmental compliance.

• Phase knowledge pays off in the field. The EPA 608 framework emphasizes knowing how refrigerants behave, how to recover them safely, and how to prevent uncontrolled releases. Recognizing that vapor can remain after liquid removal is a practical piece of that knowledge—especially for large-capacity chillers where the residual gas mass can be nontrivial.

• Historical context matters, too. R-11 is an older refrigerant with a rich operating history in large chillers. Its pressure-temperature chart is a classic example of why technicians learn to read PT data carefully. Even though many regions phase out certain substances, understanding their behavior helps you troubleshoot and manage systems that still use them or that have legacy components.

• Real-world numbers aren’t a gimmick. Saying “about 100 pounds” isn’t about guesswork; it’s an anchored figure derived from typical system charges and the physics of vapor at a given pressure. In practice, you may see some variation, but the principle holds: residual vapor adds to the system’s total mass after liquid is gone.

Let me explain the broader takeaways with a quick, friendly tour of how this fits into a tech’s day-to-day

• Read the PT curve, not just the label. When you’re looking at R-11 or any refrigerant, the pressure-temperature relationship tells you what’s possible in the vapor phase at a given pressure. For 0 psig, you’re dealing with a low temperature, but the vapor isn’t gone. It’s a reminder to check physical data sheets and system specifications before assuming anything about mass or capacity.

• Don’t confuse mass with volume. In a large chiller, the volume of space that vapor can occupy isn’t negligible. The mass of vapor depends on the temperature and pressure, yes, but it’s also about how much gas is trapped in the headspace and internal piping.

• Keep the workflow simple and safe. When servicing, plan your steps so you don’t trap vapor where it can be released or where it could condense into a liquid under the wrong conditions. Recovery equipment, proper seals, and a clear procedure keep the job clean and compliant.

• Tie this to the bigger picture. The EPA 608 program isn’t only about memorizing answers—it’s about understanding how refrigerants behave, how to manage them responsibly, and how to apply that knowledge to real equipment. This kind of scenario—liquid gone, vapor remaining—illustrates the practical science behind the certification’s expectations.

A few practical tips to anchor this concept in memory

• Remember the word pair: liquid removed, vapor remains. It’s a simple mental cue to picture the system’s two-phase reality and to anticipate that some vapor mass will persist.

• Visualize a large vessel with two layers: film on the walls and a cloud of gas in the volume. At 0 psig, the vapor’s temperature is cold, but the mass is still there.

• Tie it to a rough rule of thumb. For big chillers with R-11, expect a non-trivial amount of vapor after the liquid portion has been drained. While the exact number can shift with design and charge, the practical lesson holds: expect vapor to linger.

A brief aside—how this connects with everyday refrigeration careers

If you’re just starting out or you’ve spent years in the field, scenarios like this pop up all the time. You’re not simply flipping switches; you’re interpreting data, reading charts, and predicting how your yesterday’s work will influence today’s performance. The beauty of the EPA 608 framework is that it gives you a vocabulary for those moments: a way to talk about pressures, temperatures, and masses with colleagues, technicians, or supervisors. It’s about building confidence to handle systems that aren’t brand-new, where yesterday’s decisions show up as today’s numbers.

Key takeaways you can apply now

• In a large chiller using R-11, when all liquid is removed, you still have a significant amount of vapor—roughly 100 pounds in a typical 350-ton unit, though exact values depend on charge and geometry.

• 0 psig puts the vapor in a low-temperature regime, but it doesn’t eliminate the vapor mass. Treat it as part of the system until you’ve completed proper recovery or servicing.

• Understanding this helps with safe handling, accurate recovery, and compliant operation—three cornerstones of working with EPA 608-relevant refrigerants.

If you ever find yourself staring at a chart, a gauge, or a weight on a scale and wondering how much vapor is left after you’ve drained the liquid, you’re not alone. This is the kind of detail that separates good technicians from great ones: the ability to translate a handful of data points into a reliable expectation about the system’s behavior.

A final nudge to keep the momentum going

Stay curious about the refrigerant properties you encounter. Manufacturer data sheets, PT charts, and reputable industry references are your friends. They’re not just for quizzes or certifications; they’re practical tools that help you diagnose, troubleshoot, and operate equipment safely. When you’re working with large chillers or vintage systems, a grounded sense of how much vapor remains after liquid removal is a quiet ally that keeps you in control.

In closing, this isn’t merely about choosing the right number in a quiz. It’s about appreciating the physics of R-11 under vacuum conditions and recognizing how that vapor mass shapes service decisions. That awareness—coupled with a solid grasp of EPA 608 principles—will serve you well as you move through your career in refrigeration and HVAC.