Have a Trane central system installed in 88. Model T V030 A140A0

When I last ran the A/C a few months ago it seemed to be working fine.
Usually when it fires up, you can hear a shursssshhhhh-shurrssssh
which I gather is freon starting to move within the system and you can
feel the bubbles in a tube at the front of the air handler housing.

Now when I fire it up I get no freon sound and no cool air. The air
handler is funning and the fan on the compressor unit outside is
running. I depressed the Hi Press fitting a really quick hit just to
verify there's pressure and there is.

It actually exhibited this behavior years ago when it was newer - a
few restarts seemed to get it kicked into gear, but so far no luck.

I'm not versed in A/C but am otherwise mechanically inclined, no
problem whatsoever digging into things with proper direction. Any
primary suspects I should look at before calling someone in?

Thanks for all input.