I use argon because of the smaller molecular size for pressure testing compared to nitrogen. Primarily since I have a more than adaquate supply of it as well as it is more expensive locally than nitrogen by quite a lot. . I also have the ability to vacuum to 100 microns so do it. I just try to follow the best recomendations I can find.

On modern heat pump installations I do not even mind leaving the modern systems under a five hundred pound argon test for a few days. This because I cannot get around to liking the flared fittings at the compressor side of the air to air units. Apparently the copper flare continues to slowly compress as well. So they should be torque checked in about five years.

I am not a proffessional hvac guy either. I just do not want to deal with things any faster than I have to so am a little more fussy initially. Paying some other party 1500.00 to install air to air heat pumps and not being careful enough does not turn my crank.

Almost anything I do is done to the best of my ability. You can save time with shortcuts but they can turn around and bite you as well. Especially if you are sloppy. I really dislike doing something again that could have been avoided.

There have been a lot of requests for me to do heat pumps. I am trying to get my son in law in shape to do them. It is hard because he hears of all the shortcuts being used. I have no desire to do them on a steady diet myself.

I am all for guys doing their a/c work. Just as long as they observe safety issues and use good practices. One accident with freon can mean the total loss of your eyesight. Better to use proffessionals if you feel otherwise. Generally I do no outside a/c work for others. Other than the occasional friend.

I've been using the method described by Manny since I started turning a wrench. (It seems like I started a few weeks after the wheel was invented.) I usually limit the N2 pressure to 125psi. If I'm chasing leaks, I'll push some dye into the system with the first N2 charge. Every few years I run across instructors who teach the same method (in-service continuing education courses).

Safety note: Never use an engine to pull a vacuum, R-12 and similar refrigerants will turn to phosgene if burned. Phosgene kills, painfully. No second chances!