Around 6 months ago, I bought a 2004 E53 X5 4.4. Love the car, except for a few little problems. The main one (Coming in to summer anyway!) is the air con.

Basically, both vents work fine on heating - From what I can tell. (I haven't had to use the heater too much). But, now in the warmer weather, I want the air conditioner to blow cold air. And it is, but only from the left side vent. The right side if considerably warmer.

I have googled, looked and checked for weeks but I am now at a dead end and don't know what the issue is.

I have 2 error codes relating to the IHKA. One is the AUC sensor. The other is the aux water pump

Here is what has been done:

1 - Checked the dual heater valves for continuity - Both are approximately 17 ohms
2 - Checked the voltage at the valves. 0V for heat. 0 volts for air con. (May be due to bad connections to that connector - Or maybe the AUC sensor telling it to output 0V?)
3 - Measured temperature at the vents themselves. Left goes down to around 3 degrees C. Right sits around 15 degrees C. (Ambient around 19 degrees C). Closing off the left vent makes the right vent slightly cooler. Closing off the right vent makes the left vent slightly warmer.
4 - I have clamped off the heater valve inlet hose. This was suggested by my mechanic to prove that the air con was actually functioning, and to save putting it on his machine and spending unnecessary money of parts that didn't require replacing. However, the temperatures above remained approximately the same.

Although some of the above probably all points to the dash temperature controller, I have my doubts. By clamping off the water supply to the heater valves, there should be no hot water entering the heater cores. And therefore there should be no difference between left and right vent temperatures. But there is.

My thoughts are that perhaps I have a dodgy motor on the heater distribution box (Or whatever it is called - Under the dash), but I cannot work out the air flow within the box and narrow down which motor is likely to be the culprit - Or even if it is one of the motors!

Can anyone shed some light on this? It is starting to get warm over here and I really need some cooling in the car. (Oh and being in Australia means that the right vent is the DRIVERS vent. My passengers are cool - Except it is rare that anyone else is in the car!)

Cheers!