I recently bought an 01 Oldsmobile Alero. The heater vent fan works, but only on the two highest settings, which is not a big problem. However, I just noticed that the knob that you turn to go from vent to vent/floor to defroster does not work. I can twist that knob, but the air only comes out of the vents, nothing comes out on the floor or the defrost settings.

What do I need to do to fix this so air will come out on the defrost settings to the windshield this winter? Thank you, Duane.


Answer: The problem with the fan speeds is most likely the blower resistor. This is a very common failure. It is located under the passenger side of the dash, between the blower motor and the firewall- The positions not changing on the heater - air conditioning system may be a vacuum problem, control unit faulty, or a mode door actuator. The system uses vacuum into the switch on the control panel, then vacuum is sent to or removed from different actuators in the dash to control the position of the air flow. Normally a lack of vacuum to the system will cause air to only blow out defrost and floor, so that does not sound like the problem. I would suspect the problem is in the control unit.


2002 Olds Alero
Engine Size : 2.2L
Question: I loose air flow through all vents after car has been running a little while. the fan still blows but nothing comes out the vents. Any help would be really appreciated.


Answer: If the air conditioning / heater fan is still blowing, then the air must be going somewhere. My guess is that it has switched positions and is not coming out of the center vents anymore, but maybe out the defroster or floor. This is an electric HVAC system so you may have a problem with the MODE valve actuator motor. This is what directs the airflow to the different mode positions.


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    • Guest - charlie watkins

      i have a v6 alero that both in winter and summer after about 3 hrs on the road air stop flowing, fan sounds on but no air is comingout of defrost, floor or dash vents. what would cause that

    • Guest - Stan

      In reply to: Guest - charlie watkins

      If the fan is on, then air is flowing. Sounds like your fan motor quit.

    • Guest - Salvador reyes

      In reply to: Guest - Stan

      97 cutlass suprem
      Question:every time i acelarate cold air goes down floor but wen i realeace it goes back to normal

    • Guest - Bob

      In reply to: Guest - Salvador reyes

      Your car has a vacuum reserve problem. Either the hose is broken under the dash or under the hood, or the vacuum tank is leaking.

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    ? The Benefits

    How Things Work

    Air Conditioning System Operation

    The A/C system provides the following features:

    Cooled or dehumidified air for the comfort of the occupants
    Power ventilation
    Windshield defrosting
    Side window defrosting

    During most operating conditions, outside air enters the vehicle in the following manners:


    Common Engine Codes

    Electronic Throttle Actuator Control Codes

    P0506 - P0507
    The Electronic Throttle Control (ETC) System uses various inputs from the powertrain control module (PCM). This system uses the inputs to control the idle speed through serial data circuits to the throttle actuator control (TAC) module.