Subscribe to free tech tips. Flowing nitrogen while brazing and pressurizing with nitrogen are great practices. Putting nitrogen in with the refrigerant? Not so much. Nitrogen is a “non-condensable” gas because it cannot be condensed (under normal conditions). However, nitrogen is just one of the non-condensables. First, let's talk about what a non-condensable gas is. Any gas that does not condense (change from vapor to liquid) under the normal compression refrigeration conditions is called a non-condensable gas or NCG. These would commonly be air, nitrogen, carbon dioxide, argon, and oxygen. As you can see below, our atmosphere is full of them. Non-condensables in the system will result in high head pressure/condensing temperature. They may also cause high side pressure fluctuations. The end result is decreased cooling capacity and efficiency due to higher compression ratios. The only way to remove non-condensables COMPLETELY in a small air conditioning or refrigeration system is to recover the entire charge and recharge with virgin refrigerant. You can recover the charge, let it sit in the tank for a while, and then recover the vapor from the top into another tank. Then, you can recharge with liquid only to remove most of the non-condensables, but it's a pretty inexact science. You can't remove non-condensables with a line drier. While you do remove air with a vacuum pump, you only remove the air that entered the system once you open it. The vacuum does nothing for the refrigerant you already pumped down or recovered; the non-condensables remain mixed with the refrigerant unless you are dealing with large volumes. Then, the refrigerant and NCGs can actually be separated (and the latter removed). Non-Condensables Don't Cause RestrictionsHowever… “Non-condensables” is often a term that techs use when referring to ANYTHING in the refrigerant that shouldn't be there, such as moisture (shown below), solid contaminants, and other refrigerants. Carbon buildup from brazing is a solid contaminant, not a non-condensable. Moisture in the system is moisture in the system, not a non-condensable. A high glide refrigerant blend (such as R-407c) charged as a vapor instead of liquid is a fractionated charge—not non-condensables. I think you get the point. When we use a term like “non-condensable” as a replacement for “anything weird going on in the system we can't explain,” it becomes a useless phrase. It's like saying a compressor is “bad” rather than explaining the actual fault. —Bryan P.S. – HERE is a true story about what can happen when non-condensables are indeed a problem. In many cases, issues caused by those gases are preventable. Refrigeration Without Refrigerant Read more Attic Equipment Codes Read more Market Refrigeration TXV Adjustment Read more The HVAC School site, podcast and daily tech tips |