Just an FYI on basic AC repair

I learned all this over the last couple days from reading a multitude of sources. I thought I'd try and be helpful by putting it all in one thread. My AC works again, so you know the info here is at least half-correct. This is a quick tutorial, with the good stuff in bolt.
The AC compressor pulley always has to turn when the engine is running. The pulley has some clutch friction material on it right behind the front end plate (part that is stationary when the AC is off & engine running), AKA the compressor clutch.
With the clutch disengaged, the pulley turns free and the compressor doesn't move internally.
Turn on the AC switch, and a coil is energized which engages the electromagnetic clutch and turns on the AC compressor. Note, though, the compressor clutch only works with a specified amount of air gap. Sanden spec's 0.4 mm to 0.8mm air gap between outer clutch plate and pulley.
Behind the clutch plate, you'll see a few shim washers. These are used to set the air gap. As clutch material wears & gets thinner, the air gap will grow. You can either replace the clutch with a better condition Junkyard clutch, or buy a new one. I had success with simply removing two of the shim washers & reinstalling the set. Air gap was then acceptable & the clutch started working again.
Cool, except my AC still wasn't.
So, I bought a can of R134 with a little hose & pressure gauge on it. This attaches to the LOW side of the AC - the "suck" side of the compressor, with the fatter line & smaller charge port.
I added enough refrigerant to get the compressor to turn on & off, then observed pressure readings.
Low side pressure was around 15 lbs when the compressor was running. It should be between 35-55, depending on temperature outside. When the compressor cycled off, pressure rose to 80 or so until the compressor engaged again. This was happening fairly quickly, as I was low on refrigerant.
Add more freon, following directions on the can, until you get to 45 psi or so with the compressor on. Your AC should be blowing cold.
If it isn't, you should get an AC pressure manifold set off of Amazon or wherever and learn to use it. Usually, though, it's either clutch issues or refrigerant level.

Hope this helps somebody.

Something to check before adding refrigerant (assuming the compressor will engage) and you donot have access to a gauge manifold to test system pressure. With the engine running at 1500 rpms and air blowing thru the condensor (in front of the radiator); check the temperature of the line at the refrigerant drier (cylinder against passenger side firewall on newer XJs). A general rule of thumb of what to expect after slowly adding refrigerant; would be 40-50* and a hint of frost on the line depending upon outside air temperature.