Has anyone modified the climate control system to give manual control over the recirc flaps?

I'm thinking of doing this in my 1989 (So Delanair Mk3 I believe).
It's always annoyed me how the car selects fresh air or not - I still haven't figured it out, & in all my other cars I just have the heater controls set permanently on fresh air.

I think this is how it works, but please correct me if i'm wrong:
Default position is the flaps sprung to be open inside the car under the dash, so in recirc mode.
AC control unit applies 12v to the solenoid, this sends vacuum to the recirc flaps either side of the car, closing them, & simultaneously opening the fresh air flap deep in the dashboard somewhere.

So if I simply disconnect the existing wires & put a simple 12v feed to the vacuum solenoid via a switch, I think this will work?

Does anyone know if this will cause any other issues with how the climate control system operates (i'm thinking the other automated functions might need feedback, or similar)?