BMW HVAC sucks

[vonmayr]

Originally Posted by bueller

It would be interesting to know how the system actually works, like what sensors are where and what parameters are controlled and how. I know these systems have baffles to redirect air to different parts of the cabin, and sensors, usually for the intensity of the sun on the top of the dash, and there are sensors in the AC control panel itself, however, I don't know if other parts of the cabin are monitored.

Just to show that what is old is new again. http://www.e46fanatics.com/forum/sho...d.php?t=813791

The F80 technical documentation does not address the IHKA system (as the Germans call the HVAC). But, the F30 technical documentation does, at some length, discuss this functionality in book 4, section 16 (F30 general electronics), beginning on page 72. It is logical to assume that the F80 and F30 IKHA controls are the same, or at least very similar.

http://www.bimmerpost.com/goodiesfor...ectronics1.pdf

It has some really good information that I leave to the reader to digest - but here are some highlights:
1) There is a separate IKHA Control Unit, not located with the IKHA controls
2) Rear seat temperature can be adjusted. The Front Electronics Module (FEM) evaluates the signal from the rear seat area ventilation sensor and makes it available to the IKHA control unit over the CAN electronics bus
3) There are temperature sensors located in the right and left footwells, the A/C evaporator unit, the ILHA control unit in the dash, left and right ventilation ducts, and the rear seat area
4) The front and rear stratification controls (the famed Blue/Red wheel) are potentiometers that use stepper motors to adjust stepper motors to move the air flow from hot source to cold source

Armed with this information, moving on to Real OEM website, the following details can be obtained:

1) The blower/microfilter are located behind the glovebox, which is also where the IKHA control unit resides
2) The IKHA temperature sensor is somewhere on the door side of the passenger dash
3) The F30 and F80 share many of the same parts, validating the assumption that they share the same IKHA controls

The trail for where the temperature sensors that control the rear environment are located goes cold at that point for the documentation I can find.

Hope this helps move the discussion forward in a constructive manner.

[bueller]

Originally Posted by vonmayr

...Hope this helps move the discussion forward in a constructive manner.

Excellent information. Thanks!

I lived in California for 20 years and understand the OP's issue.

I have solved the problem in the past by redirecting air vents to the rear of the cabin and tinting my windows. The tint does not have to be dark if you don't want. Llumar has an excellent ceramic window film that will reduce the transmissive UV considerably.

The problem is that the sun is so intense that the AC system is keeping the front of the cabin cool, but is not moving enough cool air to cool the rear of the cabin that is heating up due to the sun beaming in through the windows.

It would also be interesting to know if the problem differs between freeway driving and driving less congested areas. My thinking there is that if the recirculation is set to auto, the air will recirculate if the system senses pollutants in the air, which will limit airflow. Most cars have cabin air exhaust flaps usually around the tail lights. If the air is recirculating, it is probably only doing so in the front of the cabin and poor air movement is crating uneven temperature.

It is also a BMW thing, the 5 series has separate controls, and probably separate sensors in the rear compartment. I can hear a German BMW person in my head saying 'if zis feature was so important he should have bought ze 5er'.

I see with the 3 Series, there are the following temperature sensors;

- Evaporator
- Front Right Footwell
- Front Left Footwell
- IHKA Unit (dash)
- Ventilation Left
- Ventilation Right

Additionally it uses the Rain sense to also monitor solar

I don't see a sensor specifically in the rear, it looks like its integrated into the rear stepper motor (baffle) mechanism. When they say "Temperature for rear-seat area ventilation can be adjusted" I think they are just talking about the hot cold dial on the vents. Looks like the "10 Saturation potentiometer for rear-seat area ventilation" is a sensor, but it is not clear if temperature is a parameter it passes.

Off topic, could you imagine a system like this without multiplexed signaling? The car would weigh 300 pounds more for just wiring!

No system is perfect, I am sure with some messing with the controls, the OP can solve the problem. I understand his frustration, Auto should mean just that, the system automatically takes care of managing the temperature, alas life is full of disappointments.

B.

[vonmayr]

Originally Posted by bueller

It is also a BMW thing, the 5 series has separate controls, and probably separate sensors in the rear compartment. I can hear a German BMW person in my head saying 'if zis feature was so important he should have bought ze 5er'.
B.

That's probably true. Maybe a committee of Germans. Or maybe it was "We can save half a kilo without zis feature."

Originally Posted by bueller

Off topic, could you imagine a system like this without multiplexed signaling? The car would weigh 300 pounds more for just wiring!
B.

The modern CAN serial bus architecture has enabled truly staggering levels of integration and computerization of cars. For example, it's the only bus running between the FEM and the diplay unit atop the dash.

[VB5ER]

Originally Posted by RickFLM4

I live in South Florida and find the a/c works fine. I drove Audi and Lexus since 1994 before I got this M4 in July. When I first got the car I thought the a/c sucked until I moved a thumbwheel from red to blue. I don't understand the point of / need for that thumbwheel but once I moved it to blue I just left it there and everything is fine.

First lets address the fact that your car sounds awesome from the sig list. Post a pic. We're car guys. As for the blue/red wheel it only controls the temp in the two middle vents. I love having cold air on the feet and a little warmer up top. It's a nice feature. The care temp seems highly adjustable between driv, pass, and rear seats. OP might just need to fine tune his settings and leave the auto climate for solo driving. I don't think anyone on here has owned a car that was 100% perfect. I'll keep my awesome car and adjust the air as needed. #1stworldproblems.

[USAM3]

I've tinted all of my windows even the sunroof with 3M crystalline and it helps so much during the hot CA summers. Tinting all the windows has been the best thing I've done to the car as it helps tremendously with cooling down the cabin.

[mc-m3]

Originally Posted by uo813a

So I have noticed that on my e46 m3 that you have to have the Ac on to keep the cabin from fogging up. I have never had this issue with my other vehicles. I live in the northwest where it is raining most of the time but I shouldn't have to use Ac to get moister out of the air. I would have to agree not the best system.

Sounds like you have your AC setup to recirculate the air. I also live in the Seattle area and only have this issue if I get in the car wearing a wet raincoat.

[mephiska]

Originally Posted by USAM3

With other car brands you get free flowing fresh air in the cabin when the car is at speed without having to turn on the HVAC system. You can shut out the air flow altogether by engaging the air recirculating button. Simple and intuitive.

What you're describing isn't true with most modern cars anymore. They're designing cars to be as streamlined and drag-free as possible for fuel efficiency, and the type of fan-less airflow you're describing requires an inlet with positive air pressure to force the air into the cabin. This creates drag on the vehicle and reduces fuel efficiency, so instead they now make you use the fan to draw air into the cabin when you want it.

Now instead of having to muck with the recirculation button (which on older cars was a slider bar to control airflow at different vehicle speeds), if you want air you just turn the fan up or down. And you save gas. Win-Win!