Alright, here's the gist:
AC only gets sufficiently cold when I'm moving. When sitting, it usually doesn't cool at all, maybe barely. Blows fine at all times. Coolant is at good pressure and I've had it checked a few times. Here's the weird one: if I sit idling long enough with thto AC on, it eventually will stop being cool, let out a high pitched squad and shoot a spray of what I can only guess is coolant. Then, back to normal. Also, occasionally when I'm driving, it stops blowing cold and if I turn it off and turn it right back on, it's fine again. HELP!

 

Where is the spray coming from? Minivan? Are fans running?

 

I believe fans are running and the spray comes it from under the hood. Only lasts half a second.

 

There is a high pressure relief valve on the a/c compressor. When system pressure gets about 500 psi, it lets Freon out to keep stuff from getting damaged. That is the sound you hear. Either the fans don't work or the high pressure transducer isn't reading correctly so the fans don't engage when they should. Also would explain why it cools going down the road.....air flow through the condenser is good.