BMW Repair: AC Fan, serpintine belts, fan speed

Question
528i, 1997, AC Fan will not go to high.  Defrost same thing no high speed.  Recent repair:4/27/04, Thermostat housing - remove and replace, Replace serpintine belts(5pk X 906 and 6pk X 1555)

Answer
The most likely problem is the resistor block used for the fan speed, other possibilites include the computer malfunctioning, a corrupted signal from a sensor or a crossed wire/s or a bad switch.  to diagnose this problem, voltage must be checked at each connection point to pinpoint the source.
-cheers