Welcome to 2CarPros.
It sounds like a bad connections in the wiring. If you turn it on while installed and move the wiring around to it, does it begin to work? Was the connector in good condition and none of the pins were pushed in? What I would recommend is to disconnect the connections at the fan motor and see if there is power to it. See if moving the wiring around to different positions cause power spikes or loss of power.
One other thing, if the blower motor only works on high, then suspect the blower motor resister. Let me know.
If moving it does nothing, I need you to check for a good ground and power. I attached two pics below. Pic 1 is for manual climate control and pic 2 is for automatic. Check the pins shows (based on your system) for power and ground.
Here are a few links you may find helpful:
Let me know.
Images (Click to enlarge)
Tuesday, July 2nd, 2019 AT 9:22 PM