The bmcm controls the fan speeds. On my 88 Fleetwood the blower all of a sudden shifted to hi speed and I could not turn it off. After arriving at home I took all the fuses out and the fan continued to run on hi so I disconnected the battery and it quit running. I obtained a used bmcm and after installing the fan worked great. However, the next day after driving for about 5 minutes the air shifted from the dash vents to the floor vents. The air is still cool, but I can't get it back to the dash outlets. Any ideas--please let me know. JP jpw46@yahoo.com

 

Bad signal being sent to the mode door unit which is in behind the glove box. Mode door determines which vent duct the air goes to, pull out the liner and see in the motor is functioning properly.

 

Cads--Thanks for your recommendation, I'll give it a look see.

Additional information: 1. After driving for about 20 minutes I can sometimes trick the system by selecting defrost. The air will slowly shift, but not all the way, then I can select auto and the air will slowly shift to the dash, but still not all the way, but it makes it much more tolerable in this GA heat.
2. I may also have a vacuum problem also--the cruise control is slow to catch on and periodically when cruising on the hiway it will break cruise and I have to re-set. JP jpw46@yahoo.com

 

The reason for the slow change, as I have found, is the fact that the hinge on the mode door gets rusted from condensation in the hot cold chamber. When it gets rusteds the mode door will neither close or open completely. Get in behind the glove box and spray some wd40 or other lub on that hinge and free up the mode door to do its thing.