Thanks all, for your suggestions.
Paul-R wrote: ↑20 Apr 2019, 09:37
Just to finally rule out a physical blockage somewhere reconnect your original control unit but DON'T screw it back into the housing. Then try to alter the speed manually and by pressing the defrost button. Don't do this for too long as the control unit won't be getting cooled by the air flow and could overheat. But it should be long enough to prove (or not!) a point.
Thanks. I’d already tried this with all 3 control units. It made no difference so I didn’t mention it.
bobins wrote: ↑20 Apr 2019, 10:22
It's not something odd like the car thinks it's in reverse gear ? IIRC, the blower speeds up when in reverse.
You’re right, and mine switches the fan when selecting in and out of reverse, though only when the heater is in Auto (recirculation?) mode which seems correct.
GiveMeABreak wrote: ↑20 Apr 2019, 11:11
The recirculation mode in reverse, when engaged should also activate the A/C if not already whilst in reverse and the fan turns a little quicker to ensure adequate circulation of air whilst the outside fresh air is cut off in this mode. So that would indicate the Climate ECU circuit seems to be working fine.
Yes it does turn the fan a little quicker but doesn’t turn on A/C automatically. I assume though that this function is working correctly.
GiveMeABreak wrote: ↑20 Apr 2019, 11:11
I would still suggest you return el cheapo units and get a half decent one. The cheaper HMCMs (Heater Motor Control Modules) are notoriously poor quality. Your actual fan motor is obviously fine as it can be switched off and goes at full pace with one or other of the modules installed - so it remains highly likely the HMCM is the culprit.
I agree: the fan turns at varying speeds in accordance with different functions such as no hmcm installed and power/earth bridged, when switching on/off recirculation function, or when setting reverse gear. Therefore the motor is able to work at all speeds. The dashboard controls operate the heating system flaps, hot and cold settings make a difference. Which leaves the hmcm.
After buying 2 cheap Chinese copies the worrying thing is they look identical to the OEM part, with the same part number moulded and a similar moulding date mark on the plastic body. I’m concerned that buying a non-Citroen part will be more of the same cheap copied s**t. But thanks for the link, I see it’s sold by Amazon so if it doesn’t work then returning it shouldn’t be too much hustle.
That said and given the above, I’m not sure what else it could be.
I’ll order it and let you know how it goes. Fingers crossed while I wait for the postie