Does coolant continuously run through the heater core or is there a valve which shuts off the flow when the A/C or vent is used? If the flow is only on demand I am thinking about running heat once a week to keep the core flushed.

 

I think it circulates through the heater core when the temp controller is anything but absolute cold. The amount of flow is proportional to the temp **** (so think of it as a valve for all intents and purposes). Not sure if having the HVAC off stops circulation or not.

My reasoning behind this comes from what happened when I had my heater core leak. The vents only stopped smelling of coolant when the temp control **** was turned ALL THE WAY to cold. One notch above absolute cold started smelling like coolant. The more I turned the ****, the more it smelled.