Did the same thing myself at my home (1.5 ton and 4 ton systems), at my rentals, and my office. My first experience involved buying the a NEW 1.5 ton split system from a Goodman wholesaler and getting 1 of 2 willing local installers to install it. They did this without permits and did a pretty messed up job. After that, I was going to have to pay big $$$ to have the system installed properly so I started to research. I ended up buying all of the tools needed to do the job RIGHT and have had my first system running without a hiccup for 3 years now.
To be able to buy or handle refrigerant, you will need your EPA certification. Luckily you can take an online, open-book test to get your EPA Section 608 certification at EPATEST.com. You can also do a free R410 technician test, among other goodies included in the exam fee. I did this, got my card in the mail, then went to my local HVAC supply house and could buy R-22 and R-410a refrigerant. Keep in mind that the open book test is only good for servicing systems up to so many tons and if you want to be 100% legal, you should take the sit-down test for larger residential systems.
Look up the model of your condensing unit and you will find the installation manual online and it will have the calculation of refrigerant based on the length of your lineset (copper tubes). You will need to measure the length of copper tubing and determine if you need to ADD or SUBTRACT refrigerant based on your lineset length.
At a minimum you will NEED to buy:
1. HVAC gauges with hoses (red, blue, and yellow) - about $50 on eBay NEW. Check refrigerant pressures/temperature to determine superheat and subcool.
2. Vacuum Pump - about $120 from Harbor Freight for a 3CFM Dual-Stage Vacuum Pump with 25% off coupon.
3. Nitrogen Tank and Regulator - about $200 from your local Welding Supply store or HVAC supply house. You can get the regulator off of Amazon or eBay as well. Use this to pressure test your system for leaks and also to flow Nitrogen while brazing the copper lines to eliminate chances of oxidation inside the copper which will clog up the factory-installed filters and negate their presence. You will also use Nitrogen in the triple-evacuation process to clean the refrigerant piping before letting the refrigerant out of the compressor.
4. Oxy-acetylene torch setup with tanks --> Harbor Freight has a good kit with tanks - drop off empty tanks at AirGas or HVAC supply house and they give you USED, certified FULL ones. This is used to braze/weld the copper lines.
5. Brazing rod --> Stay-Silv 5 is OK for R410a systems. This is to make any connections in the copper lines. DO NOT USE plumbing solder. You could get by with older, lower pressure R-22 systems, but not with R410a systems. You need the Stay-Silv or similar. Stay-Silv 5 means it has 5% silver, higher silver content makes is easier to work, but at an increased cost. As a newbie, you will go through a lot just practicing, so stick with the 5%.
6. TIG Welding Gloves --> an oxy-acetylene flame is VERY HOT.
7. HVAC Thermometer with K-type Probe --> used to check the outside temperature of the copper tubes to determine subcool and superheat to fine-tune the amount of refrigerant charge you need.
8. Copper lineset if not included with new system. You can also use a special cleaner to clean the R-22 from old linesets out to be used with newer R410A (the only type allowed to be sold nowadays in the USA). I would recommend newer linesets though for piece of mind.
You can search YouTube for 'Dr. Zarkloff' and see how to do some common HVAC work, which will give you more confidence before you hook up your gauges for the first time.
9. Micron Gauge --> used to check vacuum on lineset, you need to hold under 500 microns to say you have a good seal and all contaminants are out of the lineset before releasing the refrigerant.
10. Or get a Fieldpiece SMAN3 Digital Manifold that includes (2) thermometers, digital gauges, and a micron gauge. It is about $300 off Amazon, but you get everything in one package. You will still need to buy some hoses off eBay though. The longer hoses (60in) will take longer to pull a vacuum vs shorter hoses (48in).
I just had laser eye surgery, so I will try to remember to post more later as I have to rest my eyes now.