why does my caravan gets hot when ac or heater on?

Check your servo. You might have two types. One for the direction of your air flow and one more for the hot and cold damper control. If you get air to your glass, face, feet and so on the first one is ok. If you get hot or cold only than it's the second one that controls the hot and cold damper flaps is bad. Good luck.

Thank you for that. What's a servo? Sorry I'm not mechanically inclined. Maybe I should of asked why does the van overheat when I turn the a/c or heat on? It blows cool when a/c on but the temp jumps immediately to HOT, so I turn off. Sam thing happens when I try heater. It blows hot then the van temp goes to Hot. Please help!

Ok, it's not the servo. Servo controls the air flow in the cabin and controls the type of air hot or cold. Sound like it's working. You might have a cooling problem, meaning radiator is going bad. Your a/c hot and cold feed of your radiator so if radiator isn't working properly than you'll have a/c hot and cold problem as well. When cold a/c is on, your engine works harder causing it to get hot. When you turn off a/c it goes back to normal, means your radiator is working just enough to keep the engine at normal temp. Here check two things. 1) check radiator, 2) check a/c electric fan behind the radiator. There are two one runs when temp hits high, and the other one runs only when your a/c is on. So run your engine to its temp range see if one fan works, next turn on a/c and see if the other one works. If not working when you have your a/c on than it's the fan that's gone bad. Good luck.

A.C condenser coil maybe clogged with dirt and bugs causing little to almost no air flow across the coils clean condenser with garden hose and nozzle if radiator sets in front of condenser clean it also so that you can get good air flow to condenser.