How do you add freon to a 1991 LS 400?

Locate black or green plastic cap at rear left side of engine bay, it may be under a black plastic cover, but is viewable without removing cover. Open valve on R12 charge hose and screw onto R12 can, the sharp needle in the charge hose fitting should be retracted fully or you will puncture the can and lose all the freon as well as freeze your fingers! Screw can on and then screw charge hose fitting onto port on low side pressure hose (green capped) Start car and turn AC on full blast and roll down Windows. If you have an electric fan, put in front of car and point toward radiator to simulate air flow across radiator. Let run a few minutes. Get a thermometer and put it in the vent and note temp. This is not mandatory, but once you start filling it, you want to fill until the temp doesnt go any lower, That is all. more freon will not make the system work better. invert can (or follow instructions on can, some require it to be inverted, others dont) and turn valve all the way closed, this lowers the needle into the seal and punctures the can, freon will not flow until you back the valve out (open) do it slowly and you will feel the can start to get very cold. You can stop the flow by closing the valve. Add 1 minute bursts while slowly rocking the can from side to side about 45 degrees, just enouhg to keep the liqued moving. Use gloves as the can gets very cold! close valve and let sit 30 seconds and note temp on thermostat. It may take a full can or just a few shots, but if the A/C is not blowing cold, itll probably take the whole can over about 10 minutes. The A/C can take up to 3 cans for a completely depleted system, but never more! There is a sticker somewhere that tells the capacity of the A/C system. With Freon about $15 a can on Ebay, it may be worth your while to get it topped off professionally, usually around 65 bucks from a small shop. If you have lots of Freon laying around, give me a ring!