Odd air flow issues

[jpilk99]

So, with summer here, AC is getting plenty of use. Noticing some odd behavior though:

With fans on full, (not "MAX AC), and not "Auto" ...and it seems/feels like I'm only getting only about 70% of the air flow coming out through the vents (only dash vents selected and, yes, the blue "cold" box is selected above).
For reasons I can't fathom, all of a sudden, the flood gates will open and I get 100% of the air flow. It's awesome. Then, a few minutes later, it goes back to about 70%.

I also notice, with all the same 'settings' above, if I turn off the AC "snowflake", the airflow goes up to the 100%.

Blend doors? Any ideas?

Thanks!

Jay

[Ruskii]

What about the air recirculation? Is it set to auto, on/off?

[Mayorchuck]

What about the air recirculation? Is it set to auto, on/off?

This. Unless you can hear that the blower motor is slowing, I would suspect the cabin filters.

[jpilk99]

What about the air recirculation? Is it set to auto, on/off?

It was NOT set to Auto.

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This. Unless you can hear that the blower motor is slowing, I would suspect the cabin filters.

Hi Mayorchuck. That would be encouraging, in that it's an easy fix. Only thought/question: If the filters are bad - wouldn't the air flow STAY bad, not fluctuate?

[oldroller]

Hi jpilk99, just went through this on my 01.

https://www.bimmerforums.com/forum/s...A-low-air-flow

The IKHA monitors temp (small left hand grill under the left digital display) and airflow via the plenum, with return air THROUGH the cabin filters.
Any restriction at the cabin filters will affect the control of the variable speed blower motor and corresponding interior air temperatures.

I had the same symptoms, erratic air speed and inconsistent temps. Replace (or at least CLEAN) your cabins filters, both sides.
I thought I had low refrigerant charge, but not so. After cleaning the cabin filters, pressures at hi/low ports were on the mark for ambient temps.


You will be pleased with the results. Full force air on MAX, variable control in AUTO according to your temp settings, and more comfort/less noise.
I have noticed lately with increasing ambient temps that the IKHA does not engage the AC compressor while in auto if desired temps are lowered (if the 'snowflake was not engaged). I assume the compressor must be manually
turned on, but I may be wrong. I'll have to look into this aspect of the system.

Otherwise, this is a marvel of interior air handling mechanisms.

[Mayorchuck]

It could even if the setting is on recirc mode. I'm sure Q has a detailed thread on it but going on memory, the system will allow outside air in for a period of time even if the setting is in the recirculation mode. Has something to do with air quality in the cabin. The owners manual probably addresses the cycle it goes thru.

[psjr]

Yep, just check your cabin filters. The system has lots of times it switches between recirc and vent without your consultation.

[740iSport303]

+1 on recirculation filters. Your description is on the money for clogged recirculation filters that are under the dash on both sides.

[jpilk99]

.... I love you guys. Thank you. Getting new filters!!!

[carnut1947]

I just bought my 99 740IL. My in car cabin filters looked original! Completely plugged. I replaced those as well as the hood filters. It's been 106 here in Northern Calif. for a week and the system in AUTO at 69 degrees works perfectly. I leave my settings in AUTO with the recirc. button also set to AUTO. Most people think when they hear the fan motor change speed when switched to recirc. that the car will be cooler, when in fact it's just closing the blend door and the blower speed remains the same.

[oldroller]

I especially like the second press/hold on the key fob for express down of all four windows and sunroof opening. Enter, fire it up, hit 'Max' for a few minutes then close her up.
Turn Max off, system on auto at 68f, and I have a half hour drive home in (as Warron Zevon put it) splendid isolation.

Sweet.

[jpilk99]

Thanks again, all. And just to confirm, there's:

2 filters inside the car - 1 in the gloxe box, one by driver's side knee area toward outside wall
2 under hood - under insulation by air ducts

?

[robo740il]

The passenger side is under the glove box, not in the glove box. It is easier to replace than the driver's side.

[Qsilver7]

With fans on full, (not "MAX AC), and not "Auto" ...and it seems/feels like I'm only getting only about 70% of the air flow coming out through the vents (only dash vents selected and, yes, the blue "cold" box is selected above).

Jay

Just to clarify & verify...the situation you explain in the quote above indicates that you are not engaging the MAX button (pre-programmed button located at the top RIGHT of IHKA which turns the blower to high & closes fresh air flaps) nor the AUTO buttons (automatically select air distribution vents & blower fan speed and are located at the bottom of the left & right IHKA buttons) on the E38.

But what you didn't say (it was asked but I believe perhaps misunderstood) is...how do you have the AUC (automatic recirculation) button set (the button on far left of the e38's IHKA row of center buttons)? If no LED is illuminated, then only fresh air is selected. If the right green LED is illuminated...the fresh air flaps are closed & only air within the cabin is being recirculated)...if the LEFT green LED is illuminated, then the fresh air flap will cycle open/closed based on environmental conditions that are being picked up by the AUC sensor in the engine bay.

If you have the AUC button set to auto recirculate (green LED on RIGHT side of button is illuminated)...then this could be the cycling you hear as the IHKA opens & closes the fresh air flap. Then if your recirculation filters (the interior ones below the dash) are clogged...then it can dramatically decrease the amount of air flow as the fresh air flaps open & close.

Below is the AUC (auto recirculation) button:

{AUC is different than the AUTO air distribution/blower speed button...as well as the MAX pre-programmed button..and operates the same on the e38/e39/e53 models}

This is a dirty recirculation filter that needs to be changed/cleaned:

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The recirculation filters in the pic below are WAY past due the need to be changed. When the interior "recirc" filters get this dirty/clogged...they can dramatically reduce the amount of air circulated into the car's interior:

[franco90]

Good thread and information on here


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