Testing closed refrigerant lineset/equipment with pressurized air instead of nitrogen

Question

Can you test a closed refrigerant lineset/equipment with pressurized air instead of nitrogen? I am guessing not but what would happen if you did?

Answer 1

You can fill the lines with anything that is compatible with all the materials used for the lines and equipment, including oil, refrigerant, nitrogen, air, water, and probably other materials. However please don't. We use nitrogen for a few reasons:

1. It's easy to get at really high pressures. Testing at 400 psi is easy to do with a nitrogen tank, and impossible with most air compressors.
2. It's a consistent gas, so the properties and behavior are well known. This includes the fact that the molecule is much smaller than refrigerants, so a system which holds nitrogen well should also hold refrigerant well.
3. It's available dry, meaning you can use it to drive moisture out of the system.
4. It won't contain dangerous flammable materials such as methane, which could cause serious problems.
5. As a bonus, it's suitable for backpurging joints as you braze them, so you don't need a separate material on hand to make quality joints in refrigerant piping.

There's probably more, that's just what comes to mind for me. To answer your specific question 'what would happen if you did [use compressed air]?' You would end up with higher levels of moisture in the system which is a common cause of HVAC compressor failures, you would potentially end up with dirt and debris in the system from the compressor, and you could end up with incompatible oil in the system from the compressor.

Answer 2

Pressurized air contains moisture levels not found in Nitrogen. We all know moisture causes rust so not a good idea to use air. Plus Nitrogen can detect much smaller leaks than air so you might not find the existing leaks with pressurized air.

Answer 3

You are asking about the supply of "gas", whether Nitrogen (N2) can be replaced by something else.

With "Air" you may mean

• dry air as the dry mixture of components we find in the atmosphere: 78% N2, 20% oxygen (O2), 2% all the other stuff (noble gases, 400ppm = 0.04% of CO2, etcetc);
• air as the mixture of dry air and "humidity" aka water: H2O ;

or in the worst case, maybe you are thinking of replacing N2 with pure Oxygen (O2).

As you may see, air is N2 plus something else. And this something else is largely O2, which is very reactive, leading to oxidation (ox-ygen ...) or O2 plus a very strong solvent that may condensate (H2O), blocking microscopic cracks that therefore will go unnoticed or getting stuck in some meniscus/curves, promoting all kind of future reactions/blockage inside your piping system.