It'll say 'with sealant'

 

I agree with these comments. If you don't have a vacuum pump and the two gauge fittings you will introduce air into the system, which should not happen. And don't add any refrigerant oil to the systems since when the R 134a leaks out the oil remains. And there are two oils that can be used, mineral oil that dissolves in R 12 and synthetic oil which dissolves in R 134a, and they are not mixable in the other refrigerant.

Since most small leaks will not leak all the refrigerant out if the system was working earlier, you don't have to start from scratch. If you do you will then also need a receiver/dryer since the system will be up to air which contains moisture, and the existing dryer will be full of moisture. If you can't do all of this it is better to do nothing until you can have an A/C tech fix it.
Larry

 

If your system still has refrigerant, and you've only lost a few ounces, it's ok to top off. You should absolutely get a set of manifold gauges, you should not touch the A/C system without a set of gauges. If you're going to drain the system, open it, to replace parts and recharge it, then you should absolutely use a vacuum pump. Do not vent the system to the atmosphere on purpose, only by accident.

 

I will just add that running the ac compressor all the time or every few weeks will help keep the system operational and reduce the likelihood of leaks developing.

I have a 2004 MDX I purchased new, it has 180,000 miles (daughter owns it now) and the A/C has never been touched. It is on full time with the climate control system. Other cars that I neglected to exercise the compressor sooner or later developed leaks. My 2009 with 85K miles has never been touched and I have been fastidious about running the ac compressor every month.