Summarize the following:
Refrigerant is very dangerous and can result in injuries. It can cause frostbite if it hits your skin. If you get it in your eyes, it can blind you. Follow all instructions on the label, including additional recommended protective gear. There are two ports on your air conditioner. You will add the refrigerant to the low pressure line port, not the high pressure line port. The low pressure line has larger tubing than the high pressure line, making it easy to distinguish between the 2. Sometimes they are labeled with "H" for high and "L" for low. In some vehicles, the low pressure line port will be lower than the high port, but this is not always the case. Most kits have a hookup that only fits onto the low pressure port, making it easier to choose the right port. The cap is the little plastic cover that seals the valve. Once it's off, make sure you put it somewhere safe so that you don't lose it. Simply click the gauge connector over the open port. You can wiggle it gently to make sure it's attached. If it's loose or comes off, try to attach it again. It's best to select a recharge kit that comes with a pressure gauge. This allows you to easily add more refrigerant without overcharging your air conditioner. The gauge will provide a reading in psi. It should have colored zones to indicate if it's in a safe range. Green means good, but your levels could still be lower than necessary to cool your car if it's low in the green zone. Your ideal pressure will be determined once you test the outdoor temperature. You'll do this when you test your system later in the recharge process. A reading of 0 means that there is no refrigerant left in your air conditioner, which will require a repair by a professional technician. Otherwise, you can charge the system yourself using your charging kit.
Put on your eye protection and gloves. Find the low pressure line port, which will have thicker tubing. Remove the port cap by unscrewing it. Hook the pressure gauge hose to the port. Check the reading on the pressure gauge. Proceed with the recharge if the pressure gauge reading is above 0.