You can't check the charge until it's running. The only thing you can
check is to see if it's totally empty, or still has some. Just punch
the valve pin and see if any pressure.
If it hasn't been out too long, a belt may be all you need.
If it's leaking fast, it won't have anything in it. But if it still
has refrigerent, if it has a leak, it's probably fairly small.
All you can do is get a new belt and go from there.
Hope your clutch didn't seaze, and thats why the belt is gone..
I've had that happen before in a chevy chevette. Put so much
squealing drag on the engine it killed it at stop lights..
I had to get out and cut it with a knife.
The longer it sits without working, the more likely you will
develop seal leaks, so I wouldn't wait too long to check it
out. You might get lucky and have the belt be the only
real problem. Might need a top off of refrigerent, but that
can be had for less than $175..
MK

As MK suggested, you need to have the belt installed to check the AC's
function.  The problem with releasing refrigerant from the schrader valve is
that even a small amount of refrigerant lost will diminish the AC's capacity
a little, and it is illegal to vent refrigerant to the atmosphere.

You should be able to replace the belt in a half our or hour or so.  With
the AC running, look at the sight glass on the receiver drier in front of
the condenser.  The receiver drier is a metal cylinder about the size of an
aerosol can with metal lines running in and out and a dime-sized glass
window on top.  With the AC running and he system fully charged, you should
see a clear liquid running past the glass.  If you see foam or nothing in
the sight glass, the system needs charging.  With the belt installed, if the
compressor is seized, you will hear a squeal, the system should shut itself
down, and the AC light on the dashboard should start blinking, indicating a
problem.

For $30-ish, you can buy a can of R134a that has a guage on it that connects
to the low pressure side of the system. Connect the fitting on the can of
juice to the fitting on the vehicle, start the vehicle and set the A/C on.
The can of juice should say that there is some amount of pressure (in
pounds). If the pressure is low, the needle ought to move, but not high
enough to make the system work. If the system has a leak so large as to make
the needls not move at all, then I think you need professional service.

The system has a fail-safe built in. If the juice (R134a) is either too low
or too high, thent he clutch will not operate, thusly the compressor is
protected by the fail safe system. It is not necessarily a problem for the
pressure to be too low because the juice can slowly seep out.

For $30-ish, you can add enough juice to jump start the system, and if it
has a leak that is a problem so large that you need professional help, you
will know in a matter of a few days (give or take). If it hasn't got a leak,
then in a few days (give or take), the system will remain working and no
further attention is necessary.

I have a '95 Bronco that the AC died a few weeks ago. It turned out that the
juice had seeped out over a very long time (at least one year, and probably
much more), and the pressure dropped below the minimum specification,
activating the fail-safe device. I went to my local Autozone/Kragen/whatever
is on the corner by my house and selected a couple of small cans of R134a. I
have a very funky hose and guage that gives me the pressure information
needed to perform reasonalby accurate charging of the system, and the two
cans would have done the trick for me at a bit under $30. Then, I found a
single large can that was the same as the two small cans, but it also
included a handy hose and guage that is way better (easier to use) than the
funky thing I have already. The large can with the guage was 2 or 3 dollars
more than the pair of smaller cans, and the guage is way easier to use. As a
bonus, the large can had directions that included an ambient temp chart that
told how much juice to squirt into the system. As it turned out, all of the
juice in the can was exactly the proper amount according to the chart
printed ont he can. How easy is that?

I had to take the van in to have the belt put on, and even they
struggled mightily with it.

It blew some cold initially, but squealed around corners and
occasionally when idling, just like it did with the old belt. I see a
milky color whooshing past the inspection window, but  I wouldnt call
it foam. The left driver vent blows cold air and they get less cold to
thr right. The right side passenger vent blows very slightly chilled
air or even warm air. Fortunately I rarely have passengers in this
car.

Diagnosis? Neither belt feels loose.