Chrysler Repair: 2000 T&C: Bleed the heater core, coolant temp, school cars

Question
We have a 2000 T&C.Heater has stopped working at idle.Temp indicates half and corresponds with feel of radiator.The heater core lines thru the firewall are both cold with engine at operating temp.Heat works ok at hiway speeds.No recent coolant service done.So...is there a valve like the old school cars to turn water on and off,separate thermostat or possibly air in system?Ideas?

Answer
Hi Tom,
There is a possibility of air trapped in the heater core pathway so you could drain off some coolant to a low enough level to drop it below the core, and then refill it. More likely is that there is a build up of crud in the pathway so while you have it partially drained you could remove the hoses going to the core and the return hose as well, and back flush with a garden hose. I believe you can get adapters to attach a garden hose to the heater hose for this purpose. There is one wrinkle but it applies only to the 2.4L engine and that is that when refilling you need to remove the coolant temp sensor and fill the system to that level, then put in the sensor. But that is probably not the engine you have in the T&C. There are no valves involved with the system.  
Roland