Any vacuum leak in the climate system will throw the system into full wide open
heat, which is called "default position" that means heater valve wide open,
vents open to defrost the windows, the only think you'll be able to control is
the fan speed, but once you're driving down the raod, heat will sneak in, even
if it's 110 F outside.
BTW, if my assumption is correct, and depending on year 190 you have, the outer
vents will blow hot air while the center vents are seat for AC..so try that.