1998 BMW 328i AC Blower dead or on and off intermittently

Most likely need a new blower motor resistor

replace the blower motor resistor. It controls the fan speeds. It defaults to high speed only when it fails.

How to replace the blower motor resistor block: Caution: Stay clear of the blower motor and resistor block (Hot). Do not operate the blower motor with the resistor block removed. 1. Disconnect and isolate the battery negative cable.
2. Remove the glove box from the instrument panel.
3. Pull out the lock on the blower motor resistor wire harness connector to unlock the connector latch.
4. Depress the latch on the blower motor resistor wire harness connector and disconnect the connector from the resistor.
5. Remove the two screws that secure the blower motor resistor block to the HVAC housing.
6. Remove the resistor block from the HVAC housing. Installation:
1. Position the blower motor resistor block into the HVAC housing.
2. Install the two screws that secure the resistor block to the HVAC housing. Tighten the screws to 2.2 Nm (20 in. lbs.)
3. Connect the wire harness connector to the resistor block.
4. Push in the lock on the blower motor resistor wire harness connecgtor to lock the connector latch.
5. Install the glove box.
6. Reconnect the battery negative cable.
7. Have a nice day!

1. Disconnect and isolate the battery negative cable.
2. From the passenger foot well area, remove the two hex screws used to secure the blower motor resistor.
3. Unplug the front blower motor resistor from the wire harness connector.
4. Pull the front blower motor resistor and its wire harness out of the plenum panel and through the cowl plenum access hole far enough to access the wire harness connector.
5. Remove the front blower motor resistor from the cowl plenum.

INSTALLATION

1. Plug the blower motor resistor into the wire harness connector.
2. Install the blower motor resistor to the cowl plenum panel by feeding the resistor and wire harness back through the cowl plenum access hole.
3. Install and tighten the two screws that secure the resistor to the HVAC unit Tighten the screws to 2.2 Nm (20 in. lbs.) .
4. Connect the battery negative cable

your blower resistor is bad

The blower motor resistors are known for going bad. Usually its because the blower starts drawing too much current. What I would recommend doing if you can and have the tools, is to check the blower motor connector to make sure 12 volts is present. If so than I would recommend replacing the blower motor resistor. Then if the same issue ever happens again and the blower motor resistor is bad again, you will need to replace the blower motor and the blower resistor as the final repair.
Here is some info about testing the resistor using a multimeter it you have one:

DIAGNOSIS AND TESTING- BLOWER MOTOR RESISTOR WARNING: ON VEHICLES EQUIPPED WITH AIRBAGS, DISABLE THE AIRBAG SYSTEM BEFORE ATTEMPTING ANY STEERING WHEEL, STEERING COLUMN, OR INSTRUMENT PANEL COMPONENT DIAGNOSIS OR SERVICE. DISCONNECT AND ISOLATE THE BATTERY NEGATIVE (GROUND) CABLE, THEN WAIT TWO MINUTES FOR THE AIRBAG SYSTEM CAPACITOR TO DISCHARGE BEFORE PERFORMING FURTHER DIAGNOSIS OR SERVICE. FAILURE TO TAKE THE PROPER PRECAUTIONS COULD RESULT IN ACCIDENTAL AIRBAG DEPLOYMENT AND POSSIBLE PERSONAL INJURY.
Both the front blower motor resistor and the optional rear heater-A/C unit blower motor resistor can be diagnosed using the procedure that follows. For circuit descriptions and diagrams, refer to Air Conditioning/Heater in Group 8W - Wiring Diagrams.

1. Disconnect and isolate the negative battery cable.
2. Disconnect the wire harness connector from the blower motor resistor block.
3. Check for continuity between each of the blower motor switch input terminals of the resistor and the resistor output terminal. In each case there should be continuity. If OK, repair the wire harness circuits between the blower motor switch and the blower motor resistor block or blower motor as required. If not OK, replace the faulty blower motor resistor block.

Here is the information on replacing the resistor:

REMOVAL

1. Disconnect and isolate the battery negative cable.
2. From the passenger foot well area, remove the two hex screws used to secure the blower motor resistor.
3. Unplug the front blower motor resistor from the wire harness connector.
4. Remove the front blower motor resistor from the HVAC unit.

Here is an exploded view of the HVAC box. The resistor is #63 in the picture and the actual part may appear slightly different:

View Full Image


If any issues such as no voltage at blower connector or damaged or melted connector at the resistor then let me know.