[Xringer]

Hi Tom,
If you absoluly can't find nitrogen (at your local paintball shop etc),
You could try air from a Scuba shop. It's very dry and pure.
It's about 78 percent nitrogen & 21 percent oxygen.
They keep it pretty dry, since any water in a scuba tank is a no-no.
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Some installers don't do a real pressure test. They take a short-cut.
They just give the system a quick shot of refrigerant and do the soap-bubble test on all the fittings.

If opted to do this short-cut pressure test, it might be a good idea to hook
up your vacuum pump and dry up the line set before letting any R410A into it.
That will keep damp air from quickly mixing with refrigerant and making some ice..

This method is illegal in most countries, since you have to release the pressure, before running your vacuum pump.


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After all the pressure testing & vacuuming is done and you are satisfied
it's dry and tight, the last step is to release the refrigerant into the (evacuated) line-set.

But, you start off the same way as above, with
"a quick shot of refrigerant and do the soap-bubble test" etc.
Before opening both valves fully..
If it's not in your manual, it's still good practice, IMHO..