Vacuum water valve

[72 K20]

Could someone tell me how many inches of vacuum are required to open the water valve ?
My truck only carries around 10 inches of vacuum at idle and I am not getting much heat in the cab .
Motor runs right around 195 - 200 degrees'.

New heater core , valve, and hoses . One hose is hot ,, the other is warm .

I hooked the valve directly to manifold vacuum and no change.

Wondering if I got a bad valve ............... tomorrow I'm going to try taking the valve out and just splicing the hose together .

Give me some things to check , tips , info !

Thank You ! Tom