I've searched these forums and checked the megathreads, nothing really seems to fit my problem.
Just picked up a '98 300. AC and heater work, however the fans like to vary a lot. Like if the fans are on the lowest level sometimes it'll blow at full blast. Likewise sometimes if they're at high it'll blow low. Sometimes it's temperamental and likes to pulsate between speeds. When on auto the AC blows consistently and doesn't fluctuate.
Any ideas what it could be? Thinking blower motor or some faulty resistor.

 

sounds like its your ac control unit.

 

Blower motor has relay inside that can also go bad. Check the attached pdf for the blower motor and how to disassemble the dashboard to reach the blower motor. It's really hard to diagnose things without being close to the car. But I assume it may be a spliced connection or blower motor relay. In case if you have to take apart blower motor, be careful of the airbag. always remember to disconnect the battery.