Fiesta Heater - Not the usual problem I think

[benje]

Hello all,

I've spent the last few days reading numerous threads across the internet regarding the HCV and the heater system in general. Seems Ford made a slight error in the design

Anyway, the girlfriends car was exhibiting the normal symptoms, i.e. only hot air no matter what position the heater dial was on. So I did the following, I checked the HCV, removed the solenoid, and checked it was free to move and that it worked (I stuck 12V across it, no issue)

Next I checked the output to the HCV, nothing, I checked the continuity from the back of the control panel to the HCV all was fine. So it seems the issue lies with the control panel. So I bought a replacment, hooked it up, and I now had a permanent 12V at the solenoid (Which is the cold setting I believe) Turning it to hot made no difference to the voltage, it stayed at 12V. Anyway, after about 5 minutes, the magic smoke appeared from the control panel and it looks like the transistor has blown up, exactly the same failure as the original panel.

So, before I fit the second replacment panel (I also have a replacment HCV) any ideas what may be causing the panels to blow up? As a test I connected my new HCV and the new control panel to see if I could see the solenoid moving, however again, it's just applying 12V to the HCV and it doesnt seem to move no matter what I do with the heater control.

There are 12 wires into the heater control, assuming 2 are supply, 2 are the solenoid, anyone any idea what the other 8 do? If anyone has a wiring diagram it would be greatly appreciated.

Thanks in advance

Ben

[Kitchski]

If your HCV pat number doesn't begin with '7N21' you may as well bin it. Brand new ones are only around £30 from a dealer. I can't be sure that it's still causing your problem, but if it's any other type of HCV it's on borrowed time. They've revised it 7 times now, and so far the 7N21 type has been 100% successful at our dealership.