I replace the air/heater fan motor today. The old one was blowing on all 3 speeds but making a nosie. The new one runs but will not blow well at all.
I thought I had a blower problem on my 1978 Oldsmobile as the blower was running, but not moving much air. I found that I had knocked a vacuum hose loose that controlled the blend doors while working on the engine. Is it possible that you might have done the same thing?
if you mix up the wires it will turn in reverse and not blow , also have seen them wirred wrong from the factory
Also check to see if the ground of the motor is clean and tight and doesn’t have any electrical resistance.
I think that’s the best bet. Turning backwards, it will blow some, but not nearly as much as it would turning the correct direction.