[greg64]

Originally Posted by nonstop

Just food for thought here - we have a cable controlled temperature switch now (right?). What about putting one of those valves in the heater line and using the temperature switch (modified) to control the valve?

I've had that same thought. Use the existing temp control to modulate the valve, and fix the damper in the heater box so that all the air passes through the heater core, all the time.