Hello, got a noise and poor cooling?  I assume you have R-12.Check the
service ports(on the hoses). If these ports have threads, and black caps ,
you got r-12.Your van has a switch that prevents the compressor from coming
on when refrigerant level gets too low .This protects your compressor.  The
belt will turn with the pulley at all times.When switched on the clutch
face will pull in and now turn the compressor.A weak magnetic coil can
cause a chatter.This face is on the front of the compressor,.You can also
turn it by hand and see if bearings  make noise or is rough in any of its
travel(engine off). A bad oil leak will show up by looking at the underside
of the engine hatch. Oil will be thrown up  by the compressor in the pully
area.Check the compressor mounts to see that they are tight. All four of
them.A loose mount can make noise.If you still got noise, adding a few
ounces of oil may fix this. If you are getting a bit of cooling, your
compressor is on. Go to the front left wheel well and look for the reciever-
dryer. It is a cylinder with 2 hoses. Grab each hose at the same time and
measure the tempatures with your hands. If you are properly charged up,
each hose will be the same tempature. An under charge will have the hoses
different tempatures.The rear going hose will be warmer.If in doubt, remove
the 2 screws that hold the reciever-dryer to the frame. There is a site
glass on the top of the cylinder. Maybe a mirror will help here without
removing the screws.W/the a/c running there should be no bubbles in the
site glass. Charge up till bubbles diaappear.Thats abut all you can do
without major repairs.