I knew something about AC systems at the time I ran across that tool in a catalog... enough to know that the chance of being able to replace a leaking valve WITHOUT the hassle of taking all the refrigerant out... looked like 'the best thing since sliced bread'.

That tool will work provided there is room to physically attach and operate the tool. Similar tools are available for manufacturer-specific valve sizes (ie: GM) and for R-134a fittings.

Does the tool replace the valve core or the entire schrader? Either way, I'd love to see how it works in not losing refrigerant. Got a link?.

Just the valve core. It's basically a two-chamber cylinder that screws onto the valve. The core is unscrewed, then retracted into the upper portion of the chamber. Then the lower part of the chamber is isolated via a ball valve, then the upper portion is opened to remove the old core and insert the new one.

http://www.fastenal.com/web/products/detail.ex?sku=0454314

yeah, those tools are great, and the one linked to provides a place to attach your hoses to for rapid recovery/vacuum. must faster to evacuate, and reclaim refrigerant with those tools attached. I have several of them and they work great... but as mentioned, they are only usefull if there is room to use them. (several brands of equipment I work on has the service valves so close together that you can't use them.)

If someone knew that.. it might be worth changing the position of the valves....when things were already opened up during a flush, etc...

snap on has a set of adapters with their tool... pricey though...
http://buy1.snapon.com/catalog/item.asp?store=snapon-store&item_ID=52668&group_ID=12079
same kit from master cool along with other sets available.
http://www.amazon.com/Mastercool-MAS81290-Universal-Remover-Installer/dp/B000TQ6PE0

I just replace the valve cores on principle whenever I open a system.

I totally agree with that ... but have never thought to include it in a list of things which should be done at that time...

John, cool tool! Is the recovery, evac faster due to core removal thus larger opening? What's the mechanism that grabs the valve core look like? Is it spring loaded?

Are valve cores all the same? Do AC valve cores use a different seal material depending on refrigerant types? What about a tire valve core? Can they be used in an AC system? Where do you buy a quality valve core?

The schrader valves are usually on metal pipe plumbing. Their position is not changeable unless you are willing to do some cutting and precision TIG welding.

I am pretty sure you can just by that which can be inserted into a flexible line... and cap the metal pipe one..
I think I bought one when putting together three hang on systems to cool my KarmanGhia about 1988...
However, I am the proud owner of a pre WW2 Miller Tig welder... LOL

For some reason, I am having difficulty in understanding the above.

ya know what? I've never really paid attention to the mechanism in the thing... it works, it grabs the little ball on the end of the schrader... hmmm I'll have to look at it now. I know the tire cores are different, too long. I've never used any on cars, only a/c home/commercial systems. I usually carry 20 or so spare cores with me at any one time. always pull out the cores prior to welding in the linesets, and ya flow nitrogen during welding,so it's good to have the tool attached for this. makes the flow smooth, and simple to pressureize after and quick for the evac!

I am pretty sure you can buy a shrader valve as just a shrader valve which is on a tube with the ends just long enough to stick into a rubber AC line and use hose clamps to secure it. It will probably have beads running around those ends and the hose clamps made to fit it will have a ' spacer arm' on them.. which will put the clamping pressure at exactly the proper spot on the beaded section.