heat D.O. No suction at vacuum cable to heat controler. Should fingers feel.

on 1997 Dodge Ram 2500

pulled vacuum cable off heat controller.

2 answers
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