How to I clean the blower vents on my fas257s2a window ac?

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.

Vent doors not open correct

You likely have a clogged AC condensation drain tube due to leaves or maybe a mouse nest. Remove the AC blower motor and clean the drain hole out at the bottom of the blower motor housing.

Remove the AC/heater blower motor and clean out the mouse nest or leaves you will find in the housing.

remove the vent and clean inside

BEST TO LET BMW DEALERSHIP REPLACE HEATER BLOWER IF NOT MISTAKEN YOU HAVE TO DISCHARGE AC SYSTEM TO REMOVE REFRIGERANT LINES TO REMOVE BLOWER MOTOR COVER.THIS IS NOT HOME FIX.BMW CARS NOT EASY TO WORK ON.YOU HAVE TO BE BMW MECHANIC TO WORK ON THEM.

is it an automatic climate control unit?

Besides drying clothes, dryers also remove lint. This fine, fuzzy material can cause trouble because it blocks dryer lint traps, clogs vents, and fills blowers. Lint can also gather around and in the tracks of the drum rollers, or in and under the pulleys and the drive belt. The result is poor clothes drying or -- sometimes -- no drying. To avoid lint problems, clean out the dryer's lint trap system every time you use the dryer.
To clean the lint screen, remove it from the unit. The screen may be located near or under the door sill, or in the top of the dryer near the control panel. It can usually be removed by pulling it up and out of its housing. Remove the accumulated lint to clear the screen; then replace the screen.
The exhaust vent also collects lint. Vent maintenance involves cleaning the lint from a screen in the dryer's vent exhaust collar and/or at the end of the exhaust vent where it sticks out through a basement window or through an exterior wall. To clean the screen, remove the clamp that holds the vent to the collar, or back out the screws that hold the vent to the collar, or pull the vent straight off an extended collar. Clean the screen thoroughly and replace it in the vent assembly.
To clean the vent itself, use a vent-cleaning brush (available at hardware stores) to pull out any lint deposits. Also check the vent run to make sure that the vent piping or tubing isn't loose at the joints, or -- in the case of flexible plastic venting -- isn't sagging between hanging brackets. Breaks or sags cause undue strain on the dryer's blower system, and can cause drying problems. If the vent pipe or tubing has become clogged with lint, remove the lint by pushing a garden hose or a drain-and-trap auger through the vent to a convenient joint. Disassemble the joint to remove the debris. With this procedure, it isn't necessary to disassemble the entire vent to find the blockage.You can head off problems before they become too serious by providing routine maintenance for your dryer's door gasket, thermostat, timer, and other frequently used parts. Let's discuss how to service these important components in the next section.  
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there is a vent opening linkage for the top vents if you had removed panel for sterio install this linkage might have come loose or the wiren to electric relay to open top vents came loose

also vent doors on front of a/c vents are turned to the closed position

also quite possible the passenger blower motor compartment door in side the blower mode has something blocking entrance

also your truck might be equiped with a blower motor filter i read that these need to be changed out during normal filter replacements the filters for ford i didnt know they started using filters for a/c on reading this since 2000

if you are sure vent is ok ..did you try a load with vent disconnected??...there is a chance there is something blocking air flow in lint screen/blower housing ..remove the 2 screws under filter remove all back screws remove 4 screws holding blower housing in place ..you then can pull complete housing out back