Low air output from heater

[Rus]

Hello everyone!

Now that the colder weather is here, I've had to use my heater a few times. What I've noticed is that when the heater is enabled, the airflow from all dashboard vents is about 1/3 of what is the norm for fresh-air operation. If a higher blower setting is selected, a noise is emitted from the upper part of the dash. This noise really resembles air rushing through a small slit almost. No noise is present without using the heater. Is there an air door that directs air through the heater elements toward the top of the dashboard? My theory is that the motor for this door is not openning it fully and thus cutting down the airflow significantly. I've searched through manuals and sites (thank you Shogun), but all I can ever find are the automatic climate control heater unit repair instructions for an E32. Since my E34 is equipped with the basic HVAC system, the climate control manuals do not apply. I must mention that the heater maintains the correct temperature in the cabin even with the reduced airflow from the vents. So in summary:
1) Has anyone dealt with this kind of issue before? and 2) Is there some sort of schematic or photo of the heater unit and its motors?

Thanks in advance!

P.S.: The car does NOT have a microfilter.

[Eric540i]

I believe that the condition is normal.
It's part of BMW's "stratified" air system.
See:
http://www.bimmer.info/forum/showthread.php?t=17966&highlight=stratified

[Rus]

I believe that the condition is normal.
It's part of BMW's "stratified" air system.
See:
http://www.bimmer.info/forum/showthread.php?t=17966&highlight=stratified

Thanks for the reply!
I am familiar with the stratified air system operation and control, but am basically concerned about the low air flow I'm getting. I would expect to see no difference in air output at various blower settings compared to just cold air operation. It seems that as soon as I select the warm air setting with the driver/passenger controls, the air output drops off drastically. So is this normal after all?

[Eric540i]

I'll admit that I'm not sure that the lower air-flow is necessarily normal but mine's the same and a friend's 530iA M60 is too.
Once I'd learned about the stratified system I assumed that a more 'ambient' heat ensued rather than the standard 'blast'.
I could well be wrong.
I'm aware that there are several "stepper-motors" that control air-flow and some have a tendency to become loose in their mounts, but - like yourself - I've never found a sufficiently detailed map of where these are located.