I seem to have an ongoing saga with my climate control heater, i'm now out of ideas - need some advise regarding possible electrical faults.
Had the typical erratic heater blower motor behaviour about 12 months ago, removed what looked like the original FSU (Hedgehog) and replaced with a cheap Ebay jobby. Fault fixed.
6 months later Heater Blower wont work, no erratic behavour like before so think maybe the actual blower motor has failed. So removed the FSU and bypassed it, the blower motor did work when supplied 12V. I decided it must be the cheap FSU that failed so bought a OEM version and installed it. That solved the problem.
Full history here 2002 E39 525i Heater Blower Diagnosis?
Roll on just two months and the heater stops working again. Very suspicious that the OEM version is unlikley to be faulty, I wonder if something may be causing it to fail, some kind of electrical fault? So I removed the FSU and used a multimeter to check out the voltages.
These are the results of tests at the connector block to the FSU.
With engine off / on:
PD between power wire from fuse and earth wire: 11.9V / 13.9V
PD between power wire from fuse and chassis/ground: 11.9V / 13.9V
Resistance to earth down earth wire: 0.1 ohms
With engine off / on:
Power drawn by blower motor when FSU bypassed: 15.5A / 17.5A
PD between control Signal and chassis/ground:
2V one bar on display
3.25V five bars
4.7V ten bars
7.6V Full On
With the engine on control voltages were approx 0.3V more.
After doing all this I reconnected the FSU, and very suprisingly everything worked Okay again, I thought maybe a loose connection, and was happy, but less then a week later, stopped working again.
Have removed the FSU again tonight and checked the motor works again by bypassing. Reconnected the FSU, does not work.
I also noted that with the FSU connected, as soon as the heater controller is turned on the FSU gets very hot, hand burningly hot!
I can return the OEM FSU for a replacement under warantey - but what is the point if this is not the root cause and something else is causing the FSU to fail. However looking at the voltages I recorded I can't see what could be causing it to fail. I am only an amateur dabbling - any more knowlegable folk got more ideas???