I'm trying to figure out why my heater wont work. A/C works fine, switch to heat and it still blows cold air. Ive noticed this was held ziptied by previous owner. it looks like it should have vacuum hooked to it. there is obviously something not right with this and I dont know how it is supposed to be. I dont have any idea what it is. could someone point me in the right direction, please?

(this is at the left rear of the engine bay.)