Depends on what vents you speak of not working. You have panel, defrost and floor, any one can take air from where you want. TWO flapper doors involved in there too. Look at the disassembled unit pic given. The round section to the left that looks like top and bottom are cut off the round has a flapper in it that controls floor and defrost and their overlap, turned off it forces all air through panel vents. The vertical rusty shaft and door shown at the split apart just to right of fan is the outside intake flapper I'm thinking. If the heater is on and that flapper is not closed then air is not forced through heater at all. Flapper must be switched to blow air through the core for heater to blow hot. That condition if wrong will result in air blowing but not cold. Then left half round flapper must be in correct place to put output hot or cold where you want it out of the three locations. And of course the outside intake must be clean of trash.
Like they say, the blower even if new motor will not blow like a factory one will, and any air leaking at duct connections needs fixing with foam to seal them up, doesn't take much leaking to lose what little you have with a worn blower motor.
Buy a new one and like you threw money away, I've long said there is room in there for someone really hot to make a business model work. Putting out new blowers that put out a great quantity of air at reasonable cost could make someone a millionaire overnite. All the companies that make replacement motors put out utter crap, new they barely touch medium of the dead motor even on high. It's impossible for you to find blowers that work like the ones in new cars and no reason for that other than ultra cheap bastard company that would rather rip you off. I personally would kill for a good blower; it is the biggest factor in crap a/c performance in summer once you have everything else working fine but you can't fix that part of it since no one makes a really good motor.