pulled vacuum cable off heat controller.
heat D.O. No suction at vacuum cable to heat controler. Should fingers feel.
on 1997 Dodge Ram 2500
Is problem defrost only? Are you working at the in dash control unit, or under hood? You say vac. cable,, you mean vac. tubing (*cluster of 5*) on back of controller,, or single vac. hose under hood? Really need to know this for a more accurate answer!
have a smoke test done to find leak if you can't find the other end