How to Evacuate an AC system, Full Vacuum Procedure
1,174,671
Published 2019-10-01
This video is a collaboration with Paul from The Engineering Mindset channel. Check out Paul's video on how a vacuum pump works here: • Vacuum Pumps Explained - Basic workin...
The goal of a deep vacuum is to get EVERYTHING out of the system, including non-condensable gases, oxygen, water vapor, and other contaminants in the air. There isn't really such a thing as a true "vacuum," which is the absence of molecules; however, the vacuum pump creates negative pressure, which forces molecules to move towards the area of lower pressure. We measure vacuum in tiny units called microns; one micron is equivalent to one-MILLIONTH of a meter of mercury column. Atmospheric pressure is equivalent to 762,000 microns, and the vacuum pump should pull below 500 microns.
Before we even hook up a vacuum pump, we need to make sure we have a clean, dry, and tight system that's free of solid and liquid contaminants. To do that, make sure your copper is sealed and that you are purging with nitrogen and flowing it while brazing. The system also needs to be leak-free before you connect the vacuum pump, and you can verify that a system is leak-free with a pressure test and a bubble test at joints. Eventually, the decay test will reveal microscopic leaks, which is normal.
For best results, use a modern two-stage vacuum pump, large-diameter vacuum hoses (greater than 1/4" and not a manifold or refrigerant hose), a core remover tool, and a high-quality vacuum gauge that reads in the micron scale. You also need to check the vacuum pump oil level and quality; change the oil if it's opaque or the level is low. Then, connect the micron gauge to the pump and pull below 50 microns to confirm that the pump is working. It's also a good idea to utilize the gas ballast when you're working on a potentially wet system. A system that's known to have water in it can benefit from the use of a heat gun to speed up the boiling process under low pressure.
To connect to the system, make sure there's no pressure on the system. Use the core removal tools to remove the cores from the system. From there, you can use a one-hose setup or two-hose setup to attach the pump. If you're pulling a vacuum on the evaporator and line set, a one-hose setup will suffice. However, a two-hose setup is ideal if you're pulling a vacuum on the entire system. After you remove the core from the side you're pulling the vacuum from, remove the end of the tool and connect the hose. Connect the hose back to the vacuum pump and attach your micron gauge to the system (as far away from the pump as possible); you can use a brass adapter with a core depressor to attach the micron gauge.
Then, you pull the system below 500 microns and isolate the system by shutting off the core remover tool. You will then do your decay test, where you make sure the system pressure doesn't rise. In general, pulling below 500 microns, isolating for 10 minutes, and making sure the pressure doesn't rise above 1000 microns will suffice; we pull below 300 microns and make sure the pressure doesn't exceed 500 microns in 10 minutes. However, the sensor in the micron gauge can be affected by refrigerant and can give strange numbers. (You can break the vacuum with nitrogen to stop that.)
There are some myths about pulling fast, deep vacuums. One myth is that you'll freeze water in the system, and the other is that you'll damage the oil by pulling too deep. POE oil actually requires a very deep vacuum, and you won't damage the oil unless you pull below 1 micron. You CAN freeze water in a vacuum, but there is usually enough heat in the HVAC system to prevent that from happening.
Read all the tech tips, take the quizzes, and find our handy calculators at www.hvacrschool.com/
The vacuum pump shown in this video is the NAVAC NRP8DI - www.trutechtools.com/NAVAC-NRP8Di-Vacuum-Pump
Micron Gauge Shown is the BluVac Micro - www.trutechtools.com/Accutools-BluVac-Plus-Micro-W…
Vacuum Hose Kit and Core Removers is the BluVac TruBlu Advanced - www.trutechtools.com/Tru-Blu-Advanced-Kit-BluVac-L…
Core Depressor - S10767 - www.trutechtools.com/Accutools-S10767-Shrader-Depr…
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All Comments (21)
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Great video, Bryan. So many good tips!
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Holy Cow !! All I wanted to do was to replace the AC compressor on my Volvo. I've discovered a whole universe just based upon air conditioning. completely overwhelmed.
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I'm going to be working in "startup" for hvac and this video; was so much more in depth than anything else I found online. This man took the time to explain every process of how to do it. At the same time explains why you do what you do. While everyone elses videos. they said some really wrong information that I lowkey at first thought was like okay its part of the job. This man with his videos basically called out these other "hvac tutorial lessons" and made them look like a work of fiction. I will be working my way down the entire playlist of 88 videos. Thank you so very much for your time, your explanations, and your brain power to help others succeed. Thank you sincerely. I'm a man who has earned everything himself no hand outs.. so this makes me feel respected as a newcomer trying to learn the trade, versus the other guys making me feel like i can ignore real problems and move on to get paid for doing a crap job. You are certainly a cut above.
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THIS is how you know someone knows their stuff. They explain complex things in a simple way. Thank you!
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thank you i have been in commercial hvac for 25 years and have always evacuated the same way. through my manifolds. i have been working on trane wshps recently and it takes a 1 ton 6 hours to get to 800 microns and that is with triple vacuuming it. now with your way i can do it in 10 mins and get 250 microns
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I am a retired electrical engineer. I designed radio & TV antenna systems, microwave links, and did human exposure to radio frequency energy safety studies. I like learning about other systems, plus it helps understanding my house's central AC system. Excellent tutorials, thanks for explaining terms and why it matters.
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It is so appealing to hear you explain things. Someone as brilliant as yourself (in any field, not only HVAC) who cares about sharing your hard-earned knowledge and wisdom is truly inspiring. I am someone who does not work in HVAC and still I love to watch and listen to your videos. You are a great teacher.
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Thanks for posting this video, we just did some training with our team this morning and used your video as part of the training. Our entire team was very impressed. One comment was that it is difficult to find a video that mimics the process we have as a team. Thanks again and keep up the great videos
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Man you go in deep into hvac then my instructor ever did i have a epa universal and i still learning alot more with each of your videos
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These videos are such a blessing my online HVAC course goes through a book that doesnt explain these concepts well at all. Thank you for taking the time to break down these topics its tremendously helpful.
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This is one of the greatest technical videos I've seen, period.
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Like WOW Bryan you are one of the most intelligent tradesman tech that I have ever seen. Nice balance you do not waste a word and speak with data and useful information. Great video.
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If every inspiring HVAC student watches your VERY WELL DONE INSTRUCTED VIDEOS they would be LIGHT YEAR'S AHEAD of the CLASS. GREAT JOB.👍🏻
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Wow, excellent video. Thank you for the intuitive video! I should have watched this video before my first system evacuation lab.
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Excellent teacher, and fully detailed. Couldn’t be better!
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Most excellent explanation and instruction....I'm semi retired, in my 70's, still working the trade, not as often as I used to, but still humping and I'm still learning...This video, helped me get better...My thanks to the gent that make it.
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Thank You! I'm an Electronics Technician and have been working in the field since 1997. I was falling in love with HVAC because of your passions plus knowledge and how you were explaining step by step. You have reiterated how importing larger size hoses and how to connect micron gauges away from the pump and checking no leakage before the services step done. Thanks.
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Dude - perhaps the easiest to understand tutorial on the web. Good on you sir - awesome post!
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This is collegiate level information...presented in a professional, clear way!
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Bryan, Great video explanation on how to properly set up equipment for evacuation. I once had to evacuate a low temperature drier used in a leather tannery. We had to install a new coil, which the factory had pressure tested with water. Multiple evacuations and multiple oil changes over several days just to get the coil dry. It also helps, when dealing with a wet system, to do partial evacuations, breaking the vacuums with DRY nitrogen which, will soak up some of the moisture. Also slow DRY nitrogen purge, before evacuation is started will help speed things up. Not all nitrogen is DRY. I once used up a small nitrogen cylinder, and opened the valve an inverted it when it was empty, and water ran out!
