System Description
The models of Scorpio equipped with Climate Control, named as Semi Automatic Temperature Control System (SATC) by Ford, utilise an electronic variable speed control, or Heater Blower Control (HBC). This speed control causes the speed of the Blower Motor to be variable. (The HBC is a linear voltage control device and not a PWM design).

The SATC module provides a control voltage to the HBC, this controls the speed of the motor. The HBC has a +12V supply.

Testing
Turn the Fan Control switch on the SATC panel to maximum and switch the ignition to On. The engine does not need to run.

The fan should run at maximum speed. Turn off the ignition and remove connector to the BLACK/RED & VIOLET/ORANGE wires. Turn back on the ignition and a nominal 10V should be measurable across the connector (HBC Side, not Loom side).

Turn the Fan Control Switch to mid way, the output should be around 5V.

Lastly turn the position to Minimum, the output should be around 3V.

These voltages will vary from component to component and accuracy is not important, however a reduction in output voltage for a reduction in speed setting should be shown.

If the fan is on all the time, even with the SATC off, remove the connector to the WHITE/BLUE & BROWN/BLUE wires, if the fan remains on the HBC is faulty.

If the fan refuses to run and no voltage is measured at the output, check Fuse F29 in the Main Fuse Box. If this is OK then the HBC or the SATC module may be faulty - check the fault codes here

To prove the SATC panel is OK a nominal 5V should be measured on the control input to the HBC (WHITE/BLUE & BROWN/BLUE: not HBC side but Loom Side) for Maximum and around 1.7V for Minimum.

Note the fault codes generated by SATC may not always be an accurate representation of the fault. A faulty HBC that fails 'on' all time may not be shown as an HBC fault but rather it may show as a  SATC module fault.

A known problem with early models is a thermal run away effect. In high ambient conditions the HBC overheats and shuts down. This is usually noticeable as the Blower will go on and off as it heats up and cools down. To prove this set the fan to maximum position and observe the behaviour over a period of time - if the fan slows or stops and later restarts then it is indicative of an overheating HBC. It may be possible to add additional heatsink or replace it with a later part.