These are hard on defroster elements, recirc elements and floor elements. Odds are if the manifold assist pump functions, vacum block is solid and you have good engine vacum to the switchover block, you'll find a dead element that finally went completly feetup.
Project Smoker, '87 603 powered wagon
Hauler, 96 CTD can you say torque?
Toy 73 Cougar xr7 convertible
Acme Automotive Inc.