Fix Your Warm AC: Recharge Your Air Conditioner with Freon

Your air conditioning system has two "sides" -- a low pressure and a high pressure side, depending on where you are in relation to the compressor. You'll be recharging your AC through the low pressure port. You should consult your owner's manual to be sure, but your vehicle will have a cap over the pressure ports. One cap is labeled "H" (for high pressure) and the other is labeled "L" for low. As a further safety measure, the ports are different sizes so you physically cannot attach the pressure gauge or hose to the wrong port! It's pretty failsafe, but always double check yourself to be sure.