S40 AC/Heat Fan Speed
 

2001 S40- AC/Heat Blower Fan speeds up then slows down then speeds up no matter what Fan number it is on. Have replaced the Fan Resister with OEM, but made no difference. After a while, it seems to settle down a bit, but still not does always respond correctly to changes in Fan Speed number setting. Could it be the Climate Control Module (CCM) that I have heard so many problems with, or possibiliy the Ambient Air Sensor??

Have you had the recall harness on the blower motor installed? On my 2001 there is an extra harness plugged into the wiring between the original harness and the blower motor up under the pax side of the dash. IIRC this was a safety fix where the motor would sometimes not work causing the windshield to fog up which could be dangerous. You can google recalls for the 2001 S40 to verify.

What you describe was for me the blower motor resistor. Since you tried that with no success you have to look elsewhere. I wouldn't buy a new CCM though. Maybe a junkyard one or an ebay one if cheap enough. You could also try disconnecting the air sensor to see if that makes a difference.