xantia_v6 wrote: 11 Aug 2025, 13:42
Here is an extract from the Citroen wiring diagram (sorry for the poor resolution). The compressor clutch is "8020"and the wires go to the engine bay fuse box (not the BSI as Haynes claim).
Thank you for the diagram! It's so difficult to find these. So it is indeed a direct wire from the engine bay's grey connector to the AC compressor. I can now measure that connection and verify if the wiring is damaged or not
5V means the connector has 5 contact positions. They may not have wires in all of the positions.
JN stands for 'JAUNE' french for yellow. The plug is grey but the socket in the BSM (PSF1) is yellow.
While the colours of wires tend to vary, green/yellow is always permanently connected to chassis ground.
Apart from the clutch coil failing, the transistor driver for the clutch coil can also fail. The Mk1 C2's (and C3s) have a relay running the compressor coil but the Mk2 C2's (2005 onward) have a transistor. Being a semi conductor, it may give you "funny" readings. So I would take the 12V reading with a grain of salt. HOWEVER, whatever you get at the BSM should also be at the compressor plug! So if you are getting 12V at the BSM but 0V at the compressor there is something wrong! Either you are measuring incorrectly or there is a problem with the wiring or connector.
Another failure mode is the clutch coil freewheeling diode (or flyback diode) going short circuit and taking out the driver transistor! Meaning that you will have to replace, both the BSM AND the clutch coil!
ozvtr wrote: 12 Aug 2025, 01:18
5V means the connector has 5 contact positions. They may not have wires in all of the positions.
JN stands for 'JAUNE' french for yellow. The plug is grey but the socket in the BSM (PSF1) is yellow.
While the colours of wires tend to vary, green/yellow is always permanently connected to chassis ground.
Apart from the clutch coil failing, the transistor driver for the clutch coil can also fail. The Mk1 C2's (and C3s) have a relay running the compressor coil but the Mk2 C2's (2005 onward) have a transistor. Being a semi conductor, it may give you "funny" readings. So I would take the 12V reading with a grain of salt. HOWEVER, whatever you get at the BSM should also be at the compressor plug! So if you are getting 12V at the BSM but 0V at the compressor there is something wrong! Either you are measuring incorrectly or there is a problem with the wiring or connector.
Another failure mode is the clutch coil freewheeling diode (or flyback diode) going short circuit and taking out the driver transistor! Meaning that you will have to replace, both the BSM AND the clutch coil!
I'll make new measurements tomorrow. I'm pretty sure I measured the connector on the compressor plug correctly (I mean how can one measure it incorrectly), but just to be sure. And now that I know what wire is what, I can also measure if the wire from BSM to compressor is broken on the way. If it's broken, it should be an easy fix to just run new cable from BSM to the compressor's plug
