Does anyone know what this hose and this nipple are for? I don't feel any vacuum when I put my finger on them, at least not at idle. Do I need to close them off, or connect them to each other, or ignore them, or what? '95 SC300.

 

That vacuum hose area is for the Heater Control Valve assembly (HCV). The round cylindrical top thing next to it has a vacuum diaphragm inside which articulates a little metal arm underneath. The little metal arm is connected to the actual heater control valve which your coolant lines are connected to from the back of the engine above and to the heater core pipes in the engine bay firewall below.

The vacuum lines which are currently disconnected are part of the HCV Vacuum Switching Valve (VSV). This is an old 1980's-1990's method (sometimes still used on a few new cars today but now very seldom compared to older cars) of allowing the engine computer, or in this case with our SC300/400 the climate control computer in the dash center console, to open or close the vacuum in that area with that VSV so as to make the heater control vacuum diaphragm cause the heater valve to open fully, stay partly open or stay fully closed.

On the little VSV one vacuum nipple is specifically for vacuum going IN and one is specifically for the vacuum going OUT (to the HCV diaphragm module).

I can shoot you a picture from my SC's engine bay tomorrow to show how it's supposed to be connected if no one else beats me to it first.

 

Thanks, that would be cool. As far as I can tell, the heating and cooling works normally including the automatic control, but unconnected connections are annoying.

 

In case you didn’t get another photo…
here’s screenshot of mine for references when I was taking it apart few years ago. I’ll bet your current vacuum line setup is allowing coolant flow into heater core at all times.

 

Ok, I see. Someone put it together wrong at some time in the past. That's an easy correction, I'll do that in the morning. Thanks a bunch!