Recovering refrigerant from your air conditioner has just been made much easier by the new EPA valve cans of R134a.
I've been doing a lot of work on air conditioning lately and fortunately have all the tools including a recovery tank, but most people don't have more than basic air conditioning tools. When you want to put in a leak detection dye or do any other work that requires depressurizing the system, you have to either blow the refrigerant charge off into the atmosphere or find some way to recover it. Blowing it off, besides being technically illegal (even though R134a is HFC and doesn't contain the ozone destroying chlorine of earlier refrigerant"s) is also expensive.
You can recover it using the simplest tools you have. Use an empty R134a can, preferably one with a little pressure still in it. When you hook it up to the low side of the system let a little gas leak out to get the air out of the line. Now put the can in a bucket of ice water, open the valves, and wait a little while for the gas to condense in the can. When the can feels full, change to another can and repeat until you can't get any more refrigerant out. What's left in the system is only gas under about 40 psi
of pressure, which if released can be considered 'de minimis' compared to letting it all leak out or intentionally blowing it off.
You now have R134a "vapor recovered" and as such is distilled so you can't get much purer than that. Just be careful to clear your hoses of air and moisture when you transfer refrigerant. Don' t forget to borrow Auto Zone's vacuum pump to pull a hard vacuum on the system for about a half hour before recharging it to rid it of air and moisture.
As usual: Don't mix refrigerants, don't let any more gas than absolutely necessary escape, and technically you can use recovered refrigerant only in the system it came out of. It still saves you a lot of money at about 12 bucks a pound.