Where do I add refrigerant to my 2008 Dodge Grand Caravan

Coolant and thermostat is a different cooling system than ac. First check to see if ac compressor is coming on. If it's not then it's probably low in freon. If it is you probably have a damper door actuator issue.

I always advise not to add your own freon. (Blowed the seals out of a compressor once). If compressor is not coming on. Take to certified ac tech. Have them pull a vacuum on system to check for leaks. If none found have them fully charge system and add some dye to it.(this way if it leaks at some point you can find and fix) If ac comes on and works properly you are good to go. My ac tech only charges fifty dollars to do this. If compressor does not come on he can reclaim his freon at no cost to you. Unless you state for him to trouble shoot and fix.