Chevrolet Repair: thermostat, chevy astrovan, coolant level

Question
my 1992 chevy astrovan ext abs overheats when i run the air conditioneer or when i get stuck in traffic.  i check and my coolant level is good and i run the heater to keep the temperature down.  I was told that this might either be that the coolant needs to be flushed or that i need a new thermostat .. i am willing to do both of this but i have looked under the hood to see where the thermostat is and i can't find it.  would you please tell me where i might look to find the thermostat. thnks

Answer
Hi Mil,
The thermostat is almost always where the top radiator hose connects to the engine.
But, there are other things it could be.
It could be the fan clutch, or the radiator fins could be blocked with debris, or bent over, not allowing air to flow through.
Van