A clog in the coolant system, will not keep the air from flowing. Pull the power wire off the blower motor, below the under-hood heater box. With a jumper wire, run power directly to the blade connector on the blower motor from the positive on the battery. They motor should spin-up, at full speed, since you are giving it a full 12v. If the blower motor does not spin, this is your issue. If the blower motor does power up, it is in your dash controls.
