Fire place issue

[lefty Ef3]

i just moved into a home that has a majestic wood burning fire place im going to say late 80's I'm still looking for the model number. I have 2 pellet stoves and a woodstove in my other house which I'm pretty good at running and serving them.so i figure this isnt rocket science its a fireplace This prefab fireplace has a blower which i thought was for supply heated air to the room, but when its on it blows air into the fire place just inside the doors out of the bottom, I understand the theory of fresh air supply but there is a tag on the blower that says don't operate the fireplace with doors closed so that kind of defeats the forced air part..we tried to run it with a presto log and it worked good for about a half hour and then it started letting smoke back in the room..i had the chimney inspected and it was sat i know my damper was open because i looked up in side to make sure,,the blower part has me baffled