A common problem with the Saab 900 and 93 equipped with manual controls for the heater and air conditioner, is that the fan speed may only work on setting "4" (high speed) or not at all. In this case, it is likely that the resistor pack used to limit current to the blower motor may need to be replaced.
The blower motor resistor is located under the cabin air filter. To gain access to the blower motor resistor, the windshield wiper arms must be removed, along with the false bulkhead, exposing the cabin air filter. You
will want to replace the air filter while you have things opened up to replace the resistor. Once the cabin air filter is removed, a screw that holds the blower motor resistor in place may be removed. Best access is by closing the hood. The resistor pack is shown below with a blue plastic frame.
Once the screw holding the resistor pack in place is removed, the orange and brown wires that are connected to the resistor pack may be removed. You may wish to position the wiper arm for best access. Each of these
wires has a single termination, and the connectors are different sizes to ensure that the proper connection will be established. A pair of long nose needle point pliers will work best.
Once the old resistor pack has been removed, the new resistor pack can be put into place. Connect the two single wires then the connector with multiple wires into place. The connector is keyed to ensure that the proper connection is made. Remove the "red dot" sticker on the bottom of the new resistor pack, then slide the new resistor pack into the blower motor assembly. Re-install the yellow, and orange wires, then the screw to hold the blower motor resistor in place.
Successful operation of the blower motor resistor should allow one to adjust the fan speed to operate at different air flow speeds.