a/c climate control is abnormal

Hi, I suspected my ac system in my 1997 540i doesn't work properly. When I turn on a/c, it doesn't matter what temp I set, ranging from 60F to 90F, there is no different in the air temperature coming out from the vent - it is always cold. the only way I can lessen the air temperature is by turning the round wheel on the air vent from say, 3 blue dots to 1 red dot, then I can feel the cold air lessen. Does this sound normal to you guys? Normally, shouldn't changing the temperature's degree would alter the air temperature?

Any comments would be helpful. Thanks

Mine works the same way: the A/C outlet temp is constant; the blower speed changes with cabin temp. However, the heater does change outlet temp according to cabin temp.

I suspect that later years had a blending function for the A/C. Perhaps someone can chime in here.

What is the air temp out of the other vents like?

The central vent is "special" and can output heated/cooled air or external air depending on the position of the dial. I can't quite get my head to remember how positions relate to external/conditioned air thou.

Does the heating function work with AC off?

AC system normally chill the air then use the heating matrix to warm it back up, if the heating system isn't working the system will always blow cold.

Have you got a temperature gauge you can use to measure the output air temp? It's hard to monitor changes just feeling with your hand.

Normal design for the center vent.

I believe this is normal for the earlier model e39s.
I know my '97 540 will blow hot air if I turn the dial to the red even if the A/C is on (I leave the A/C compressor on all the time because the bump in idle speeds keeps me from getting this stupid flickering oil pressure light, but that's an entirely different problem).

Anyway, I don't think you actually have a problem here. If you want hotter air, adjust the dial between the vents to the red, not the actual climate control temperature. I usually keep the climate control at 70° F and that keeps the cabin at just how I want it.