i suspect that i have a plugged heater core in my van. thier is a surging noise at slow speeds and in the winter only have cold air, from the ducts. but the rear heater works. just no warm air in the front. i have cold air all the time. any ideas should i go ahead and do a coolant flush??? any ideas welcomed.

http://www.automotiveforums.com/vbulletin/showthread.php?t=405811