A/C only works on setting 4 on 1993 Nissan Altima

when i got the car, setting 3 & 4 was working.
a month later now only setting 4 works. i can hear the
a/c compressor kick on when it's on setting 1,2,3. but no air is being blown out..what's the problem

3 answers
it could also be a bad fan speed switch
If the fan motor only works on high then the fan motor resistor is bad and needs replacement
I agree with GetrDone, it is the resistor that have gone on positions 1 & 2. The resistor pack (which all of the resistors reside for the blower) sits next to the blower motor. Here is a link sample of the resistor pack http://www.partsgeek.com/catalog/1993/nissan/altima/climate_control/blower_motor_resistor.html.
Extremely rare for the switch goes bad.