Out Of Control HVAC Controls - BMW Forum - BimmerWerkz.com
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#1 (permalink) Old 08-30-2008, 04:41 AM
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Out Of Control HVAC Controls

Ever notice that on 2007 525i's, the HVAC recirculate button ignores you when the air conditioning is on? Ever notice that stale mucky smell in your 525 during the summer? My wife said that my beemer had smelly feet and hated riding in it during the summer.... Smell Familiar? Here is a solution.....

I struggled with BMW over this engineering flaw. First, here's how it "doesn't" work. When the AC is on, BMW decided that it's best to recirculate the cabin air -- which increases gas mileage as the compressor will be engaged less -- than to pull in fresh air from the outside. Unless the inside temp and the outside temp is within a few degrees. So, no matter what setting your recirc button is on (auto, inside, outside), BMW it will recirculate inside air as long as the AC is on.

There are only two ways to get fresh air into the cabin when the AC is on.....
1) Turn the automatic tempurature setting up to 90 degrees plus....... You'll hear the vents open to get outside air when doing so. 2) Open the windows.

Even though the owner's manual even warns against using recirculated air for extended periods, the BMW hvac engineers thought they knew better and over rode even BMW's awareness of issues that causes -- such as exhaust and microbacteria buildup on the AC core -- causing that awful smell in our beloved BMW's.

After countless arguments with BMW, they insisted that it's working as designed! I even asked them to put a manual knob and cable system on the dash that would open an outside air vent (over ride hvac recirc flaps) --as long as they would make sure it was a wooden knob with a nice BMW emblem -- showing a fine example of German Engineering. BMW didn't think it was a good idea. So, I took matters in my own hands and below is the solution to the problem.

If you remove the microfilter and covers just beneath the windshield wipers in the engine compartment on the passenger and drivers side, you'll see the culprits -- a flap that opens and closes an air duct that allows fresh air into the car. When AC is on, you'll see them close. Turn the hvac off, and they will open.

The flaps are controlled by servo motors just beneath the hvac duct itself. The servo motors can be accessed from under the dashboard on each the passenger and driver side. The passenger side requires that the trim and glove box be removed to have full access to the motor. The driver side only requires that the interior under dash trim be removed. You'll see the servo just above the gas pedal within a plastic cage.

Solution: Each servo motor has three wires connected via a cable connector. One of those wires was a red wire. As soon as I saw the red wire -- I knew the solution. I cut the red wires and ran them to a manual switch which cut power to the servo motors. In short, regardless of what BMW engineers tell the intake flaps to do when AC is on and when the switch is off, the flaps won't move and fresh air is pumped into the cabin regardless of HVAC settings. To return control of recirc settings back to BMW engineers, simply turn the switch on -- returning power to the servo motors. Because they are servo motors, the HVAC computer senses what position they are in and will actuate the motors accordingly. The switch itself will not open or close them -- it prevents or allows the HVAC computer (BMW Engineers) to have control of fresh air intake. Because of this -- only turn the switch off (disabling the servo motors) when the intake flaps are in the Open or Fresh Air setting. Then put the AC on and enjoy fresh air. To reverse, turn the AC off, turn the switch on, then put the AC back on. You'll hear the vents close and begin recirculating cabin air. Hold your nose.

As far as AC performance -- Not much difference in 80 or 90 degree weather. I'm sure there's some sacrifice in gas mileage as the compressor will work harder but it's better than having smelly BMW shoes in your car. When it's really hot or when first getting into the car when parked in the sun, I flip the switch on to engage recirculation to cool it down the fastest, then revert back to manual operation once cooled. Just like our HVAC controls that worked so well in our American made cars!

Hope this helps and I'd be happy to answer any questions. That was the only feature of BMW that was preventing me from ever buying another BMW as I love the car. I just hope that they correct this out of control hvac control condition in future models as I didn't like having to re-engineer their faulty engineering.

Last edited by jcapaldi01; 08-30-2008 at 04:47 AM.
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#2 (permalink) Old 08-30-2008, 10:19 AM
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#3 (permalink) Old 08-30-2008, 10:59 AM
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who told you that this is how the system works? A BMW field engineer? The dealership?Is this only when using the "auto" mode, or will it do this in manual mode as well? Doesnt make much sense. Why put the button there if it does nothing?

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