The knob on 2002 alero will not change position

check in the side of the knob for a small screw

Air Flow Control
Air flow control is accomplished in the following manner:

• Primary control is through the function selector knob , mounted on the heater function selector switch, which is part of the heater control .
• The function selector knob has the following positions: OFF, PANEL, PANEL/FLOOR, FLOOR, FLOOR/DEFROST and DEFROST.
• The heater function selector switch combines a vacuum selector valve with an internal electrical switch.

• The vacuum selector valve directs source vacuum to various vacuum control motors (18A318) . Refer to the System Airflow Schematic and Vacuum Control Charts.
• An internal single-pole electrical switch is also controlled by the selector. The switch controls the electrical supply to the heater blower motor switch (18578) .
• The position of the function selector knob determines the manner in which the system will operate.
• Each position of the function selector knob is detented for positive engagement.
• You probably have a vacuum leak , Pull heater control panel an check for vacuum . A broke vacuum hose or The vacuum selector valve is bad ! Or check for a vacuum hose in the engine compartment being off somewhere !
  

its the Blend Door needs fixed or replaced

. Air won't blow out of the floor or center vents just defrost ? Do you have manual or automatic climate control ?
Air Flow Control
Air flow control is accomplished in the following manner:

• Primary control is through the function selector knob mounted on the A/C-heater function selector switch, which is part of the integrated control panel.
• The function selector knob has the following positions: OFF, MAX A/C, A/C, PANEL, PANEL/FLOOR, FLOOR, FLOOR/DEFROST and DEFROST. The A/C-heater function selector switch combines a vacuum selector valve with an internal electrical switch.
• The vacuum selector valve directs source vacuum to various vacuum control motors (18A318). Refer to the Vacuum Control Diagram , System Airflow Schematics and Vacuum Control Chart .
• Two internal, single-pole electrical switches are also controlled by the A/C-heater function selector switch. The combination of these electrical switches controls the electrical supply to the A/C clutch and heater blower motor switch (18578).
• The position of the function selector knob determines the manner in which the system will operate.
• Each position of the function selector knob is detented for positive engagement.
• Vacuum Control Motors The vacuum control motors (18A318):
  
  • are located on the A/C evaporator housing, A/C recirculation air duct and heater air plenum chamber (18471).
  • direct system airflow to the vehicle interior as determined by the remote climate control module or manual override.
  • The five-passenger seating configuration has an additional vacuum control motor mounted on the heater air plenum chamber to control airflow to the rear seat A/C register (19893).
  
  

goto the olds. website there you'll fine the diagram for removal or replacing the vent ,floor,defrost mech..

Usually a sign of a faulty blend door - could also be a faulty control on the dash. I would have someone check the blend doors first.

when i have seen this in the past on a friends car it was the switch it self

It sounds like you have two problems. First a question though; Is your heating and air conditioning control on the dash automatic (has two knobs that rotate and a display screen in the middle), or manual (has two levers that move up and down for driver/passenger temp and a separate fan knob and mode knob).

In response to the vents being stuck on defrost and floor, from experience i can say that the most likely cause is the mode actuator has failed. If your battery has recently gone dead, that could have brought the problem to the surface. When the battery has gone dead, the heating and air conditioning controls relearn all the positions of the actuators behind the dash when the vehicle has been re-started. If there is a position sensor failing (which happens quite often) in one of the actuators, the heating and air conditioning controls won't be able to learn the correct position of the actuator and (in your case) defaults to the defrost/floor position.

The only way to fix that would be to replace the actuator. I would like to know what type of heating and air conditioning controls you have (manual or automatic) before i say anything on the blower only working on 5.

The LH models (LHS, Concorde, New Yorker, Intrepid, Vision) do have self-diagnostic capability with the standard type heater controls. I don't know about the Sebring heater controls (my '95 manual doesn't mention it) but if you have the various controlknobs/buttons that I will describe you could give it a try.
There is a rear window defogger that is initiated by a push button with an LED light. That light is the readout, by its blinking. To begin the diagnostic mode, run the vehicle at idle with the controls set as follows: the blower speed knob should be on any position other than OFF, the temperature knob should be set in full COOL, and the mode knob should be set on Defrost mode.
To enter the diagnostic mode, press the defogger switch in for five seconds, until it begins to blink, then release it. It will continue to blink for about 30 seconds while it calibrates. If it goes out, the calibration is OK and you can skip 3 paragraphs to "Position...mix mode" below.
If the light stayed on, switch the mode knob to the MIX (defroster-floor) position. If the light stays on there is a problem with the control head unit.
Switch the mode knob to the FLOOR position, if the light stays on, it indicates a problem in the blend door or the blend door actuator wiring.
Move the knob to the Bi-level (panel-floor) position where a continuous light indicates a problem with mode actuator or circuit.
Position the knob in the MIX mode. The LED light should now flash twice then pause, and continue a two-flash sequence, indicating that the MIX mode is OK.
In the FLOOR mode the light should flash three times, meaning that the FLOOR mode is OK.
In the Bi-Level Mode, a four-flash sequence indicates that mode is OK.
In the PANEL mode the light should flash 5 times to indicate no problems there, and in the recirc-panel mode 6 times and seven times in the recirc Bi-level mode.
The temperature control can be checked by switching the mode knob to Defrost and rotating the temperture knob. If the temperature contol is OK, the light will flash faster the more you turn the temperature knob up, until the light goes out at the hottest setting.
Switch the knob between Panel and Recirc-Panel and watch the recirc door (unit under the dash). Proper operation means that circuit and components are OK.
To get out of the self-diagnostic mode, turn off the blower or push the air conditioning button once.
If this doesn't seem to apply to your control head or you get no response from an LED light for the rear defroster, then the Sebring may not have this capability. Please let me know your results if any

I HAD THE SAME PROB WITH MINE I REPLACED THE HEATER CONTROL PANEL & IT FIXED IT