1987 2.3 16v.

Its wide open and heat is pouring into the cabin. I would like to test if its the valve or lack of vacume on the line before I order another valve. What buttons should I push in the cabin to command heat (vacuum) from the red line?

Rookie question but the car is new to me and no manual etc. Hey at least I used the search function and found the source of Pompei! I just tie wrapped it off in the mean time.....94 deg outside today.

Thanks