I have been watching this post and successfully charged my A/C last night.

It took less than 15 minutes, once I figured out where everything is and triple checked the procedures before proceeding.

I picked up a Charging hose with pressure guage at AutoZone ($20) and a can of r134a ($8).


After finding the Low Pressure valve (photo below shows its location on my '01 4.4i), I started the engine, AC to max, then attached the hose as outlined and pressure read about 20psi.


I then turned the knob to begin the flow of r134a into the system and it immediately jumped to about 35-40psi (slightly greater than half of the good range on the dial, which is 25-45psi).

I let it sit for a few minutes, and the needle did not move. I check the AC inside the cabin and it was blowing cold. I removed the hose and replaced the valve cap and am happy to say I drove to work in comfort this morning.

My assumption is that, when connected properly, the hose and can of r134a become an extention of the closed AC system, and the system only takes what it needs to bring the psi up the the required level. From a product usage standpoint, it seems as if it barely took any r134a from the can, but the results were a 180 from what I was experiencing from my vents just minutes earlier. From reading other posts on this topic, it sounds as if the theories are correct that it does not take much of a loss of refrigerant to throw off the system.

I will let you know if my 95 degree+ drive home from work this evening is anything but "cool".