1991 420 SEL. Auto climate control.
How may speeds should the blower have?
Mine only has low and high. Should it have more? If so what's the likely culprit?
On auto setting it always blows high. I've searched the threads and can only find no speeds, or just low speed.

TIA

I had my 1993 400E for a few years before I realized that the auto position would eventually regulate the blower motor speed somewhere between high and low once the temperature in the car reached what was set on the thermostat wheel.

Having said that, I have also replaced two blower motor regulators--both after they stopped blowing at all in low and very little in high.

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1993 400E, 256,000 miles (totaled)
1994 E420, 200,000+ miles
1995 E420, 201,000 miles

The system is designed to be constantly variable from low thru high.

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As I suspected. However, no matter what button I push or what setting the theromstat wheel is set at the blower either runs on low or high. Since the blower is functioning I suspect it's something in the control modual itself? Thanks for the reply.

A voltage check at the plug for the blower regulator should show you who is causing the problem.

A 3 wire connector at the regulator, check the YELLOW wire for voltage changes.
Should vary from less than 1 Vdc at lowest setting to about 7 Vdc at MAX.

__________________
MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator