very easy to find, very hard to see.
when you open the hood, look to the left side of your engine bay.
you should see two metal hoses between where the battery is and the engine,
one line is a big metal line, one is a smaller metal line.
the BIG line is the one you want to follow.
work your way back toward the firewall, you will see a canister that the lines hook to. this canister will be mounted under and just to the right of a removable piece on plastic, behind the plastic houses your starter solenoid (one of them anyway)
anyway work your way back till you see this canister, the port you are looking for is mounted at an angle that faces toward the engine, it should have a black screw on cap on it. (some also have blue caps for anyone else with this issue) that is the port you will use to refill your system with coolant.
you may choose to ignore this next bit but I just did this to my truck not 4 hours ago, the procedure is as follows (assuming your system works as it should and truly just needs a refill)
start the engine and allow it to come to normal operating temp.
while this is happening take your a/c refill hose and screw the can of refridgerant to it. (it is up to you weather you pierce the can at this time or not, note that if you do decide to pierce the can that you DO NOT BACK THE HANDLE OFF!!!!) doing so will cause your $15 can of oil to spew into the ozone and kill us all! don't do it.
once you have it screwed on you can set it to the side until you're ready to fill your system.
turn on all of your a/c options to the highest and coldest settings (for those of your with the E.B. overhead rear a/c control turn it on full blast as well)
unscrew your black/blue cap from the canister and CAREFULLY attach the chuck to the nipple. (keep in mind your engine is now hot. and there are things in there that will burn you. not to mention moving parts like your fan blade, and serpentine system that will remove digits and eat them like I eat Twinkies. mind your body parts and mind where you rest the can of coolant as connecting it is likely much easier utilizing both hands.)
once you are satisfied that the hose is securely attached (if you haven't pierced the can, do so now) slowly start to turn the handle backward to release the coolant into your system. (keep opening it until you hear the WOOSH of the gas leaving the can)
this is another good time to mention a little trick. take an old shop rag and soak it in warm water and wrap it around the coolant, this will keep the can from icing and make the whole process to a little faster)
if you have one, attach a thermometer to the air vent to confirm the air temp. is falling, or do what normal people do and use your hand, or a helpers. human skin is amazing at telling when temperatures change.
don't be surprised if your system takes more than one of the small cans either. some take as many ans three-four. (DO NOT OVERFILL YOUR SYSTEM!!!! don't be a cheap-wad, spend the extra 4 bucks for the hose with the gauge on it. it very well may save your life. and that's no joke.
after you are done with the first can disconnect directly from the vehicles inlet and screw on the cap (it's not like a bread tie, yes your car NEEDS it.) and check for leaks, leaks will make themselves known as a sound similar to air leaking out of a punctured tire.
clean up and your all done. hope it helps.
