156 heater fan not working

[mekcaff]

Hi, I am new to this forum and a new 156 owner.  It's a good little car but I can't get the interior fan working. Trouble shooting so far includes, in this order: 1. replaced the heater/aircon control panel, 2. Checked all fuses and relays,  3. Replaced fan (old one had seized) 4. Replaced fan resistor. Still not working. Noticed the windscreen has been replaced so sensor could be not working???  Would love suggestions that backyard mechanic could solve. Just wondering if I have missed something simple?  Is there a temp sensor somewhere?  Maybe this was solved in a previous post. Can anyone direct me here?
Thanks in advance.

[Citroënbender]

G'day, it's something that would be readily diagnosed with either Examiner or MultiECUScan.  You can see the current fan setting in Parameters of most HVAC diagnostics variants. 

Most cabin fans seem to use a positive feed that is unvaried, and modulate the grounding of the motor to achieve speed control. So you should be able to back probe the fan plug with engine running and find 13.7V or so, on one of the two feed wires (when measured to chassis ground).  If you do find the correct voltage, the problem exists elsewhere and diagnostic computer might be the fastest fix.