308 Heater blower fan not working

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Donor 2020
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Joined: 22 Nov 2020, 21:41

308 Heater blower fan not working

Post by Tom309 »

I hope this helps if others have a problem with the fan (especially the removal of the fan resistor!)

On a 2013 308 (P7) the heater fan was not working. Having looked at other posts about heater blowers for the C4 (C4 heater/air con not working) on this forum it seems to be a similar system to the Citroen. Note that this 308 is a dual zone automatic a/c model.

The fan supply comes from the fuse box via a relay that only energises when the engine is running. This supply goes via the red wire to the fan speed regulator (same thing as the fan resistor, but a more complicated semiconductor circuit). This supply is linked directly to the brown +fan wire (inside the speed regulator). The black fan -ve wire then returns via the control transistor inside the speed regulator to chassis (0V) by the green/yellow wire. There are also 2 small control wires going to the regulator. See attached Fan_regulator_circuit sketch.
With the engine running, I checked for a supply at the speed regulator (to ensure there wasn't a problem with the supply fuses or relay), measured red to green/yellow - about 14V, so OK.

Checked for supply to fan (brown to black), nothing!
So suspected the fan speed regulator may be the problem. Tried to remove the regulator. It's mostly hidden, so it was pulled, pushed, levered,.. No joy, but lots of frustration...
Checked on the web for any information on it's removal - nothing. Later on, I discovered that it is removed by pushing the small black tab (identified by blue arrow on picture below) to the right (opposite direction to ident. arrow!) so that it clears the white tab (red arrow). Then simply slide the regulator up (direction of yellow arrow) and then pull out.
As a spare speed regulator had been bought before my arrival, tried that, made no difference.

To eliminate the fan as a problem, an indicator bulb was connected in place of the fan. This did not light up on any fan setting.

I had read on the web that the fan may not work if some of the air flaps are stuck, so I visually checked these by removing and peering round various panels around the console. All seemed to move, but could not see if they moved to their full extent.

To confirm that fan is actually ok, 12V was then connected directly to the fan by using a battery charger. The battery charger output is 5A, so won't get the fan to full speed, but it should at least make the fan turn at lower speeds and it is current limited.
The battery charger went to current limit, but the fan didn't turn. So though, knackered fan.

Unplugged fan (red arrowed shows connector position, wiring already moved), then removed fan by pushing the black tab (yellow arrow) towards the centre of the fan and rotating the whole fan.
As I expected the fan to have a seized bearing, I tried rotating it by hand. It turned normally!! So tried powering it directly again. As soon as it was connected to the battery charger it worked :? Checked the fan opening in the car for anything that may have jammed the fan - nothing.

Connected the fan back into the car using the old speed regulator it continued to work. Note that at start-up there is a short delay before the fan starts to turn; there must be a soft start in the regulator.

After this checked the brushes and bearings, all looked ok, but put some spray grease on the bearings just in case. After several journeys the fan is still working.

So conclusion:
The fan seemed to have been stuck / jammed for an unknown reason, with the speed regulator shutting down its output to protect itself / the fan, so I didn't read an output voltage.
Not sure why the light bulb didn't work, may have been a dodgy replacement as I'm unsure which regulator was in use at the time.
Still puzzled about the jammed fan though...