Overheating/fluctuations with vintage air.

[Smokey burnouts]

If you've seen all the recent post I've made about having temp problems.... You know I've been chasing this for a while!! Well 2 radiators, 2 thermostats and lord knows how many trial and errors with other ideas I finally have a steady temp gauge at a safe temp.

What I have discovered is that in order for the system to work right I have to leave the tempature selector (on factory non ac controls w/ vintage air kit) on the "heat" position If I try to run the AC or even leave the selector in the "cool" position the electric valve cuts off the coolant flow to the heater core which then I think is creating a vacuum and causing the system to surge and have temp spikes.

I'm not sure if the vintage air kit is working/installed correctly or is this a common problem? Any guys running the vintage kit have any ideas??

Thanks
Daniel