Heater Control Valve

[hbastro1994]

I have a 1994 AWD Astro Van. Inside of my climate control the main vacuum fed comes through the fire wall and splits off to two sides of the climate control. The left side and the back side (six rotary vac lines). The left side attaches to a plug (with two lines connected), which is a plunger switch. When the temperature slider is pushed up for heat and down for cold this switch simply applys vacuum to the heater control water valve which controls the flow of coolant through the heater core. I"m not able to find a replacement plunger switch at the wrecking yard (or complete climate control panel), so as long as i keep this green vac line plugged (so as not to mess up the actuators for all the dash vents) any problems with not having a vacuum line connected to the heater water control valve located on the passenger side of the engine?

Also, is the heater control valve always opened so water flows through heater core and then when vacuum is applied to it, it closes off the water through the core?

With the motor running and heater on, i noticed that I get heat with no vacuum applied to the heater control valve, and if i use my vacuum tester to pull vacuum on this control valve I still get heat. So does that mean the heater control valve is stuck open?

What is the downside to not having functioning vacuum available at the heater control valve?