I probably shouldn’t be providing any advice on A/C re-filling because I barely know what I’m doing myself, but I know enough to know that you should use a set of gauges and monitor BOTH sides (LOW and HIGH) while charging your system. I’ve rented a MasterCool set from AutoZone twice now ($100 deposit and you get it all back when you return the set). Or - you can buy this same set (which seems to be decent quality) for right around $100. If you rent a set, make sure the nuts on the valve body are tight before you use the set. Last year I had the LOW side valve turn completely out on me, spewing pressurized refrigerant straight outward! Good thing I wasn’t standing directly in front of the gauges AND I was wearing eye protection! Otherwise, re-charging is fairly straight forward:
A.) Fill a small container (twice the diameter of the can) with hot tap water.
1.) Close BOTH valves on the gauge set by turning clockwise all the way (no need to over tighten).
2.) Connect the gauge lines to the car’s ports (they’re different sizes, so you cannot mix them up)
3.) Retract the piercing pin on the tap and screw the tap onto the can
4.) Attach the center/yellow hose to the can.
5.) Retract the pin on the tap to allow the refrigerant to flow into the yellow hose.
6.) Slightly unscrew the yellow hose until you hear a faint “hiss” to force out any air trapped inside. Re-tighten the hose.
7.) Place the can into the hot water bath. It will sink into the water nicely at first, but float as it discharges.
8.) Start the car, put A/C on HIGH, fan on HIGH, choose recirculate. Keep windows and doors closed (driver window can be open). I think ideally the engine is running at over 1000 rpm +
9.) Open the LOW side valve (BLUE) on the gauge set. NEVER NEVER NEVER touch the HIGH side (RED) valve!!! HIGH SIDE STAYS CLOSED ALWAYS! If you open this valve the can will probably explode!!
10.) Watch the gauges and wait for your LOW and HIGH side readings to fall within the acceptable ranges for your current ambient temperature and humidity. More than one can may be necessary. Don’t add too much. Don’t “finish off a can”. Only charge the required amount. Overcharging is just as bad as undercharging. See MasterCool.com for a table of charging values (see page 3):
11.) BUT PLEASE DO SOME READING ONLINE FIRST BEFORE ATTEMPTING ANYTHING AND UNDERSTAND THE COMPONENTS OF YOUR PARTICULAR CAR’S SYSTEM FIRST. ALSO, GET A FEEL FOR WHAT YOUR A/C SYSTEM IS CURRENTLY DOING because you could have a dead compressor or a frozen-up orifice tube, or a bad Tx Valve, etc.
12.) ALWAYS WEAR EYE PROTECTION and GLOVES. I’m thinking of buying a full-face shield after having that valve blow out on me last year! Keep in mind that frostbite is a possibility.
13.) ALSO KEEP IN MIND THAT THE (Schrader) VALVES ON THE TEST PORTS (where the gauges get connected) CAN LEAK CATASTROPHICALLY WITHOUT WARNING! I wouldn’t hover over the tops of these valves (especially the HIGH pressure port - which is more in your face than the LOW port which is usually tucked away somewhere), and I wouldn’t stare directly down onto them, either. Make sure you re-install the plastic caps when you’re done.
**** This is just a LAYMAN’s advice. No professional experience included here. BE CAREFUL! ****