HVAC 150 Vacuum p17 Example 5 Triple Evacuation

Summary

The video demonstrates one version of the triple-evacuation method for removing moisture and contaminants from an HVAC system. The presenter emphasizes that the method consists of nitrogen purges and vacuum pulls—not a process in which nitrogen absorbs moisture.

Main Points

• The goal of evacuation is to leave the system low-pressure, clean, dry, and leak-free. The presenter identifies moisture as a potential cause of acid formation, coppering of surfaces, and refrigerant leaks.
• Nitrogen helps move or loosen water vapor so it can be purged from the system; it does not absorb moisture.
• Nitrogen pressure should be kept low—roughly 2–5 psi at most in this demonstration. Excessive pressure may cause water vapor to condense back into liquid. The presenter says nitrogen pressure could help melt ice if water had frozen inside a system, but describes that situation as highly unlikely.
• Triple evacuation is widely discussed, but it may take extra time and is not necessarily the best method for every situation. Follow the manufacturer’s instructions if they specify it.

Demonstration Setup

• A regulated nitrogen cylinder is connected to one side of the system, and a vacuum pump is connected to the other through large vacuum hoses.
• A micron gauge tracks the vacuum. An added valve lets the presenter isolate the gauge during nitrogen purging to protect it from oil or other contaminants.
• The presenter applies Nylog to external connections to help seal fittings and reduce the risk of leaks. He says it is applied externally rather than put into the system.

Triple-Evacuation Procedure Shown

1. Purge with nitrogen: Flow a small amount of nitrogen through the system. The presenter recommends a longer purge if substantial moisture is suspected.
2. First evacuation: Stop the nitrogen flow, seal the system, and run the vacuum pump. In the demonstration, the system reaches about 1,000 microns.
3. First nitrogen break and purge: Isolate the micron gauge and introduce nitrogen until the system reaches about 3–5 psi. Then let nitrogen flow through and out of the system to carry out water vapor.
4. Second evacuation: Stop the purge and pull a vacuum again, waiting until the gauge falls below about 1,000 microns.
5. Second nitrogen break and purge: Reintroduce nitrogen to about 3–5 psi, then flow it through the system again. The presenter says the purge duration depends on the amount of moisture and that opinions vary on how long to run it.
6. Third evacuation: Stop the nitrogen, run the vacuum pump for a third time, and continue to the desired vacuum level. The demonstration reaches 383 microns.
7. Isolate and test: Close the valve to isolate the system from the pump, turn off the pump, and perform a 15-minute pressure-rise test.
8. Charge the system: After the test, close the vacuum gauge and charge liquid refrigerant into the liquid line, weighing the charge before returning to normal charging procedures.

Sources and People Mentioned

• Presenter/narrator: The only speaker heard in the subtitles; not named there.
• Jeremy Smith: His article on triple evacuation is recommended for its coverage of the relevant math and science.
• Brian (Bryan) Orr: His articles and podcast on triple evacuation, including its pros and cons, are mentioned.
• EPA exam: Referenced as an exam where the term “triple evacuation” may appear.
• Manufacturer instructions: Mentioned generally as the authority to follow when they specify triple evacuation.