no heat out of the vent?

[MouseOnJuice]

not sure where to put this, but i've got a 1973 merc marquis. air doesn't blow out of the front vents no matter what the control lever is selecting. clear across the selector the heat acts as if it is on defrost, and never changes until its in off position. defrost, hi-lo, vent, heat, all blow out the top window vents. hi, med, lo, switch works, the floor vents blow, but nothing out of the front vents. does this sound electrical, or vacuum related to you guys?

[rwhite65]

can u look up under the dash? My 65 is very simple, cable to a little flapper door.....not sure on the 73, but worth a try to see if maybe the cable came un-hooked.
Ryan

[MouseOnJuice]

l figured out the problem, thanks for the input though, the vacuum supply line off the manifold tree had a small leak in which l detected with propane, it was just enough to not allow the diaphragm to open enough

thanks