Heater/AC Fan Only Works on Speed 4

[dnorris5]

The car in question is a 1991 318is. The fan for the heater and air conditioning only works on speed setting 4. Based on my reading in this forum, the problem is usually caused by a faulty blower motor resistor. However, the measured resistances are in line with the specs (0.4, 0.9, 1.7 ohms).

I am looking for insight into how to proceed. Do I look at the center console switch? Or, is there a connection between the blower motor and resistor which might be faulty and is bypassed when speed setting 4 is used?

Thanks in advance for your input!

[av1]

are you measuring across the coils or on the tabs?

there is a safety switch that opens when the resistors overheat.
it probably needs to be cleaned with a little sand paper.

[witeshark]

The switch resistor may have failed.