[Desertdan]

I am looking for some general info as this is my first BMW. When AC is on (its basically always on here in AZ), the blower seems to cycle automatically. It will make a lot of noise, like fan on high, inside the dash, but not much airflow, then about every 45 seconds, good airflow will come out for about 3 seconds. Then back to the "flow" inside the dash. It does this all the time no matter what changes. So my question is - is this normal? I have been researching and it looks like it may be the final stage resistor, but the symptoms are constant, not erratic like many of the other posts. Any info would be appreciated.

[Surly73]

IMO, if it's making noise (but lacking airflow) then it isn't the final stage unit. What you describe sounds a lot like when the system is switching between recirc and outside air sources. Have you overriden recirc on? Are you in Auto Recirc mode (the A inside the arrows)?

When switching between modes, I think there is a time when outside and inside intake flaps are both closed, leading to noise and no airflow. Perhaps this short span is creating the illusion of no flow, or you have a fault with one set of flaps.

Turn the AC off (no snowflake), manually set a medium-high fan speed, and then use the manual recirc control to test for airflow and otherwise proper operation from both air sources.

Note that auto rercirc will turn recirc on and off based on fumes in the air, which is why I ask. Also note that even manual, forced recirc is not always on inside air. It opens to outside air for x seconds out of every y, with x and y varying based on AC setting and outdoor temperature.

[Desertdan]

That sounds like it might be the issue. However, when AC is on, there is no difference between any of the airflow settings (Auto, recirc, or outside). Is there some regulator that controls that function that may be faulty. I will try the system with AC off and see if persists. If it senses fumes, is that maybe a filter issue?

[Desertdan]

So if the recirc is in manual and off (no led's lit) the outside vents should be closed and inside open, right?

I turned off the AC button and played around a bit. No matter what mode, it seems that the inside vents are automatically opened and closed (or at least minimized). I can never get them to just blow full tilt for more than 3-5 sec. Is this normal?

[Surly73]

Originally Posted by Desertdan

That sounds like it might be the issue. However, when AC is on, there is no difference between any of the airflow settings (Auto, recirc, or outside). Is there some regulator that controls that function that may be faulty. I will try the system with AC off and see if persists. If it senses fumes, is that maybe a filter issue?

Maybe you have some kind of issue affecting recirc.

Even though it doesn't show it, the system will go to recirc in AC (snowflake) mode if the outdoor temp is really high or if there's a large difference between the set point and current inside temperature. It doesn't illuminate any lamps when making this decision, but it's subject to the "fresh air for x every y minutes" rules that apply to manual recirc.

With AC (snowflake) off, and AUC (auto recirc) off, there are no automatic recirc decisions made so you can better troubleshoot what's going on. Maybe your recirc-mode intake flap is never opening and that's what your real issue is. Every 3 minutes the outside air opens briefly and you've got some cooling again.

[Surly73]

Originally Posted by Desertdan

So if the recirc is in manual and off (no led's lit) the outside vents should be closed and inside open, right?

I turned off the AC button and played around a bit. No matter what mode, it seems that the inside vents are automatically opened and closed (or at least minimized). I can never get them to just blow full tilt for more than 3-5 sec. Is this normal?

If AC (snowflake) is off, and no recirc button lights are lit, it should be on outside air. If you pull the cabin microfilter under the hood, you'll be able to feel the airflow entering the passenger side opening in the cowl. The higher the fan speed the more you'll feel.

If the (A) is lit, that's automatic recirc based on pollution detected. This is not the same as automatic recirc when AC (snowflake) is illuminated.

If the (recirc) is lit, it is in manual recirc and should be inside air almost all the time, subject to the air freshness rules which change based on AC and outside temperature.

Take a read through this, and note the rules I mention on page 24:
http://www.bawarec.ru/manuals/3er/e9...3er-e90-17.pdf

[TOWBOYZ]

means ur blower motor behind your dash is going bad.

[Desertdan]

It sounds like it might be cycling as described on P24 for temps above 6 deg C, except the intervals are much smaller. I wonder if this points to a faulty AUC sensor.

[Surly73]

Originally Posted by Desertdan

It sounds like it might be cycling as described on P24 for temps above 6 deg C, except the intervals are much smaller. I wonder if this points to a faulty AUC sensor.

If (A) is off, the sensor is inactive.