Heat blows cold air after ten seconds?

Most common reason for that would be a thermostat that is stuck open and doesn't let the coolant get hot. It's a known issue with the modern Chrysler, Jeep, Dodge vehicles.
On the 3.7, the thermostat housing is down at the bottom of the engine block on the front. To replace it, you first drain the coolant. Then remove the two bolts that secure the housing to the cover. Then you clean the surfaces off and swap the thermostat. Make sure the bleed hole is installed with it to the top.