In my Loyale on the passenger side engine compartment there is mounted a vacuumn tank that is used to operate the levers for the hvac. My heater would not switch from heat to windshield today so I checked it out using the wet finger test.

 

I could feel vacuumn in the hose before the tank and when I connected the tank output hose directly to the tank vacumn input hose, bypassing the tank, the levers worked.

 

Now it generally isn't my experience that smart car makers put in useless pieces and Subaru is a smart car maker....right???. But my hvac levers switch without the tank which leads me to question if it is necessary at all. Does it just even out for variations in vacumn with engine speed?

 

Is something like this available at the average car parts store like Schucks or Auto Zone?

Without the tank your inside vents will go all wonky when you go up hills; the engine vacuum is reduced at large throttle openings. It's annoying to say the least.

 

There is a check valve mounted inside the tank on the engine side. Yours is probably stuck closed. Mine failed stuck open. You can probably just drill right down the nipple and open it up. Then go to your FLAPS and buy a check valve for a couple dollars and put it in the engine side hose.