I have a 99 Mercury Villager GS. I had to have the front blower motor replace recently. The replacement motor does not put out 1/2 the volume of air of the old blower. The mechanic said that it could be a leaky “air box”. The old blower put out plenty of air at the time it quit working. Are there other things that could be causing this decrease in air flow. It’s the same no matter what the setting (floor, top, etc.)
It may have been wired backwards. If the blower wheel is spinning backwards, it will put out some air, but not nearly as much as it should.
If there is no difference in blower speed than it is most likely a resistor. If it changes speed but no volume then it could be the shop put in a reman motor. Not all reman parts do that well. A new motor might fix it.