Disconnect the electrical connector for the climate control system control unit See M70 CLIMATE CONTROL SYSTEM CONTROL UNITWith the ignition ON, turn the distribution knob to the bi-level (completely to the left).After about 10 secs. turn the knob to the feet position (completely to the right) checking that the voltage between pins 1 and 21 is between 9.6 and 14.4 V whilst the motor is turning.Repeat the manoeuvre in the opposite direction.Also check that the voltage between pins 13 and 7 is between 4.75 and 5.25 V.