If you have the heater valve disconnected from its vacuum supply, you should defalut to full heat..at least that's the design. It's messy, but drain a bit of coolant off (there's a brass bung on the pass. side of the block, down low and toward the back)and disconnect the heater valve and check it, also check to be sure that the heater core is unobstructed. The vacuum reservoir, by the way, is the hero sandwich shaped plastic thing mounted to the cross member that runs underneath the engine. It's probably a foot long and 4-5 inches wide, with rounded ends. Your car also has a vacuum pump--that thing near the battery--because turbos produce pressure, not vacuum, under acceleration. Accordingly there is a one-way check valve (location escapes me) that keeps the pressure/vacuum on opposites of the fence. But before you tear into any of that stuff, investigate the heater valve. And good luck!

-Steve