heater control valve?

[BerniniCaCO3]

I know our cars don't have one.
Now, it seems to me, summers could be cooler still if I didn't have full heat going to the heater box: even if there's 1/32" of plastic door separating it from the air flowing past my a/c evaporator.

And --PLEASE correct me if I'm wrong--but the flow of coolant through the heater box is passive and not forced? That is to say, like electricity, it's a "parallel" flow circuit and not 100% of coolant has to pass through it? Whereas, for example, if you blocked a radiator hose pressure would spike.

So where I'm going with this is... would there be any problem, really, if I put in a valve with a lever and just cut off the flow going to the heater core? A brass fitting from the plumbing section, insert it in that long rubber hose that goes from the waterpump bypass to the heater core (unless... which direction does coolant flow through the heater core? I'd want to sever the inlet hose, not the outlet, although once flow ceases, cutting the outlet might actually be equally effective), turn the lever, and voila, no coolant to the heater core, no heat in my dash, and maybe observably colder air conditioning?

Good idea?
If a bad idea, why/ what might this do?

It would be a manual heater control shutoff valve-- no automated system, just when it gets colder, I'll need to remember to open it again.

[sly]

I would put it a T valve and set up a bypass instead. I would also rig it to be able to adjust it from within the car (manual choke cable). The pressure buildup behind the valve may not be real bad, but it might be enough to burst hoses at WOT.

[gadget73]

The heater core is not full flow. If you shut it off, the engine wouldn't overheat or stop moving coolant to the radiator. Trouble is, the coolant temperature sensor is in the plumbing to the heater core, so if you shut off the flow it would not get a flow of coolant across it, and things won't act right. A bypass loop would be better. Three valves, two to the heater core, and one in between those lines. Shut the valves going to the core, open the one between the lines to connect them, and run with it. Or just make sure your heater control cable is properly adjusted and you should be good. I can get 40 degrees at the vents in my car and I have not re-sealed the blend door. It might seak another degree with R12 or rebuilding the blend door seals but honestly I'm OK with 40 degree air driving down the road.

[drhill]

Three valves, two to the heater core, and one in between those lines. Shut the valves going to the core, open the one between the lines to connect them, and run with it.

I've done the simple version on cars before - just one valve. I would think you could get away with two T's on this applicaton - once you shut off flow to the core it will go through the bypass hose naturally right? I was planning on doing this once I replace my heater core...

[gadget73]

you could, but I expect it would make heat performance suffer in the winter since some of the coolant can simply bypass the core. On my own car it would be near impossible to actually fit all that stuff. I've got two metal lines running under the intake to a pair of Z shaped hoses in the back that go from pipe to heater core. Its tight enough back there without trying to wedge more plumbing in. I have a heater core restrictor (a washer) to keep the core from blowing up and call that good enough.