something has to be blocking the vents.
It is likely the duct work how ever it can be the fan has come off the fan motor
Loose connection or blower motor? Bad blower motor? Loose fuse? Bad fan switch?
Heater core
Failed blower motor, resistor or switch.
when a blower motor only works on high, it is usually due to faulty resistor board. Should be located in the duct near the blower. the purpose of this is so the air blown by the blower keeps the resistors cool.
it is due to the difference in the air intake and impeller construction.
Is it the blower motor or is it the fans in the front?if its the fans they will come on at anytime to help cool engine down better.If its the blower motor for the interior heat and air you got a electrical problem. Is it the blower motor or is it the fans in the front?if its the fans they will come on at anytime to help cool engine down better.If its the blower motor for the interior heat and air you got a electrical problem. If it is the blower motor for your heater then it is definatly you blower resistor
Resistor on the heater blower motor has failed
Should under dash on firwall near blower motor.
to get more air in to the carb, rather than having to come in from the front of the vehicle, it goes through the blower to the carb
You most likely have a bad blower resister..........
possibly a blower motor. or switch