I have a '03 Dodge Grand Caravan Sport AWD that the heater only blow hot air when going down the road. Van has a new radiator and new thermostat. Sometimes the blower will not kick on for a few

SOURCE: air conditioner blower motor resister on dodge grand caravan

in my 2004 grand caravan it's behind the glove box and left of the blower motor. disconnect the wires first then remove the 2 screws to pull out the resistor unit. First make sure you have removed the negative of your batterie. I had the same pm that prevented the blower motor to operate in any speed. I hope this will help

SOURCE: 2000 dodge caravan heating problems

if you are sure that your heater core is not restricted. then try to recalibrate the climate control panel. if your a/c system is not working then DO NOT ATTEMPT THE RECALIBRATION it will make your lights on climate control panel flash codes forever.
to reclaibrate the climate control panel just have the engine running. turn the mode to vent, the temp to cold, the blower on high, then press and hold the rear wiper wash and wiper buttons at the same time until the panel lights up then wait about 2 minutes for it to run completly when completed. turn off ignition and then restart the engine try to se if you have heat again. if it doesntwork post the codes it gives you after the calibration test.

SOURCE: Dodge 2002 Grand Caravan V6 3.3 engine overheating/no cabin heat.

Replace the bad radiator hose first.  Second- get you special formulated anti-freeze dye from the auto store and pour it into the radiator.  Third- make sure you got all the air pockets out of your system, cause the coolant system won't work with air pockets in it.  Fourth- Check for leaks by looking for the colored dye.  If it's not the radiator hose, then could possibly be a pin hole in your radiator.  Would suggest replacing all the radiator hoses at the same time while you got the coolant system disconnected, cause you don't want to have to come back and replace another hose in a few months.

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SOURCE: Heater blower motor replacement -1997 Dodge Grand Caravan

Remove the cover plate on the passenger side of the heater box, 3-4 screws.
Unplug the motor assembly, remove 3-4 more screws that hold the motor in place and pull it down from its position. Get an aftermarket motor and installed it in the original housing with the original squirrel cage.
Installation is the reverse of removal.

SOURCE: 2001 Dodge Caravan heater blows cold air when stopped

Have you checked the coolant level? What you describe is exactly what happens if the coolant level is low. When stopped at idle, hot coolant is not circulating through the heater core, so no heat. As the engine increases in rpm's when you pull away from the light, the water pump is spinning quicker, and some coolant is making it to the heater core. So check the level, and if it is low, keep an eye on it to see if it drops again. That of course indicates a leak somewhere. Get it fixed, as overheating the engine leads to costly repairs and worse case a new engine. Let me know how you make out with this.

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