Blower motor works fine but why low airflow to the vents?

There are several possible reasons why your blower, vent, defrost, AC, and heater might stop blowing air:

1. Blower Motor Failure: The blower motor is responsible for blowing the air through the vents. If the blower motor fails, you will not get any airflow from the vents.
2. Blower Motor Resistor Failure: The blower motor resistor controls the speed of the blower motor. If the resistor fails, the blower motor may stop working or only work at one speed.
3. Fuse or Relay Failure: A blown fuse or faulty relay in the blower motor circuit can prevent the blower motor from working.
4. Control Module Failure: The HVAC (heating, ventilation, and air conditioning) control module is responsible for controlling the blower motor and other components. If the control module fails, it can prevent the blower motor from working.
5. Vacuum Leak: If your vehicle uses a vacuum system to control the vents, a vacuum leak can prevent the system from working properly.
6. Broken Blend Door: The blend door controls the direction of the airflow. If the blend door breaks or gets stuck, the air may not flow through the correct vents.
7. Wiring or Connector Issues: Faulty wiring or connectors in the blower motor circuit can prevent the blower motor from working.

94 CHEVY Silverado ????,heat/ac fan not blowing. K1500?????? Hear clicking when selecting l'm, SET high but not blowing! WITH AIR OR NO A/C? FIRST IS FUSES, MAKE SURE THE BLOWER FUSE IS NOT BLOWN.
EASY NO? CHECK ALL FUSES FIRST. ON ALL ELECTRICS FAILING OF ANY KIND.
BAD FUSE, BAD WIRINIG , BAD CONNECTIONS. OR EVEN BAD RELAYS TO THE BLOWER OR BAD SWITCH BLOW.
THE OLD CARS , HAD A SPEED BLOW , RESISTOR BLOCK
THAT FAILS ON ALL SPEEDS BUT HIGH, SO ITS NOT THAT.
OWN A VOLT METER????
HERE IT IS, ANY OF THIS CAN FAIL THIS OLD
WE USES A VOLTMETER TO FIND THE POINT OF FAILURE.
A SHORTED BLOWER MOTOR CAN BLOW LEFT SIDE TOP
FUSABLE LINK.RIGHT FUSE BLOWN MAKES THE CONTROLLER DEAD.

resister either defective or wire incorrectly probably, try running jumper wire to motor to see if it has full speed.

Does your model have a cabin air filter ?
Is it possible the blower is not running on the right circuit in the resistor ?

Sounds like the blower motor FAN cage came lose or broken? could be bad blower motor itself ???

If the blower motor is capable of working on all the speeds but you only get wisp of air out of the vents then the fan side of the evaporator core for the a/c may be coated with crud and debris which is restricting most of the air that the blower is moving. Usually this problem comes on fairly slowly until one day it is realized that hardly any air is coming out of any of the vents even with the blower on high speed. The blower may even sound like it is working harder than it should to create this little bit of airflow. The fix for this is to remove the blower motor and look into the plastic air plenum with a mirror or flexible borescope and check the a/c evaporator for a thin coating of gray crud. If it's present then I use compressed air and a long blow nozzle [bent to get close to the core] and blow the crud loose. You may not get it all but usually you can blow out enough of it to get back 90% of your airflow. If however your blower doesn't work on every speed then you may have other electrical issues that are preventing the blower from reaching full speed.

the relay may be fine, it could be a resistor pack that is bad (if it's like what happened with my 2001 Cav [low and med1 did nothing, but med2 and high worked fine] there's a little modular board in the blower fan housing wedged at the front of the passenger side floor (waaaay up there) you'll probably have to pull the blower motor out to get to it, it's not a difficult thing to do yourself, but it's in an awkward position -- the cost (again if it's the same as for a 01) was ~$35+shipping online, and $65 from a local parts store (probably best to call to ensure prices)

try the blower resistor

probably the vent in front of the blower motor lose, check that first.