My '95 SL's blower motor will only run on the lowest two speeds. It doesn't matter if the system is set on auto or if the blower speeds are manually selected. The system still blows cold air on a/c and everything else seems to function properly. Is this a controller unit problem or a blower motor issue?

Don't know on MBs but that is usually a sign that the blower resistor is shot in an american of Japanese car.

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dtf
1994 E320 Wagon (Died @ 308,669 miles)
1995 E300 Diesel (228,000)
1999 E300 Turbodiesel ( died @ 255,000)
2006 Toyota Tundra SR5 AC 4X4 (115,000 miles) rusted frame - sold to chop shop
2011 Audi A4 Avant (165,000 miles) Seized engine - donated to Salvation Army
BMW 330 xi 6 speed manual (175,034 miles)
2014 E350 4Matic Wagon 128,000 miles
2018 Dodge Ram 21,000 miles

Where is the location of this resistor?

I don't think my SL is equipped with a traditional style blower resistor. Vehicles with electro/mechanical controls usually are, but I'm pretty sure mine is microprocessor controlled. That leads me to believe that the problem is probably in the climate control unit itself.

I'd sure like to hear from someone who knows for sure. It would save me a lot of diagnostic time and money.

I really appreciate the input, however.