Citroen C5 X7 mk3 climate control heater fan fault

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Paul-R
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Re: Citroen C5 X7 mk3 climate control heater fan fault

Post by Paul-R »

Y Cymro wrote:
17 Apr 2019, 23:58
So pull the connector off the control unit and bridge the two heavy cables in the connector?
Yes, exactly that. Then start the engine and see what speed the heater motor runs at. If it runs at maximum put the control unit back on and see whether you can manually raise the speed to max.

Also, check what speed the motor runs at, both before and after the bridging trick, by pressing the defrost button.

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Re: Citroen C5 X7 mk3 climate control heater fan fault

Post by Paul-R »

crapday69 wrote:
18 Apr 2019, 06:36
If I hit the defrost button or try and change the speed manually it just stays the same. The only time the fan runs faster is for that second on startup, then it goes to a low setting. Think I would put it in to get sorted if we had really bad winters, but the car still heats up hot in about 5/6 minutes.
If you could I'd like to know the result of the manual bridging test as in the previous post. I'm willing to bet that it will run at full speed without a problem. This points towards the control unit or, possibly, the CC ECU getting duff information from one of the sensors and then sending the wrong instructions to the control unit.

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Re: Citroen C5 X7 mk3 climate control heater fan fault

Post by Y Cymro »

Paul-R wrote:
18 Apr 2019, 09:02
start the engine and see what speed the heater motor runs at. If it runs at maximum put the control unit back on and see whether you can manually raise the speed to max.
Also, check what speed the motor runs at, both before and after the bridging trick, by pressing the defrost button.


With the bridge in ola evthe fan runs constantly on maximum speed, as I’d expect. Re-fitting either the original control unit or the Chinese replacements makes no change to the speeds as expliNed above.
Interestingly, when I switch on manual recirculation the fan with either control unit goes a little faster than when on auto recirculation. Also, noticed today due to the warm weather, the fan speeded up considerably for a few seconds before reverting to the slower, fixed speed which is the problem. I’m tempted to buy a Hella/Behr, but it’s hard to know it’s a genuine item as the Chinese are copying everything!

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Re: Citroen C5 X7 mk3 climate control heater fan fault

Post by Paul-R »

Here's a thought. When was the last time that the pollen filter was changed? With the control unit physically removed during the bridging test there's an extra opening for air to get in and out. If the filter is blocked that could be your real problem.

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Re: Citroen C5 X7 mk3 climate control heater fan fault

Post by Y Cymro »

Haha, already replaced the pollen filter as I had my face under the dash! Fault is the same with old or new filter, and with the filter removed.

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Re: Citroen C5 X7 mk3 climate control heater fan fault

Post by Paul-R »

I'm rapidly running out of ideas!

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.

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Re: Citroen C5 X7 mk3 climate control heater fan fault

Post by bobins »

It's not something odd like the car thinks it's in reverse gear ? IIRC, the blower speeds up when in reverse.

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Re: Citroen C5 X7 mk3 climate control heater fan fault

Post by GiveMeABreak »

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.

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.

Some of the cheaper ones have been known to smoke badly and others have the thermal fuse placed too near the thermal coils so have failed within weeks.

Get a decent one and you still can return it if not happy. Hella/ Behr one here £40:

https://www.amazon.co.uk/5DS-351-320-01 ... ay&sr=8-12

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Re: Citroen C5 X7 mk3 climate control heater fan fault

Post by Y Cymro »

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.
GiveMeABreak wrote:
20 Apr 2019, 11:11
Get a decent one and you still can return it if not happy. Hella/ Behr one here £40:
https://www.amazon.co.uk/5DS-351-320-01 ... ay&sr=8-12


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

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Re: Citroen C5 X7 mk3 climate control heater fan fault

Post by Paul-R »

It's a shame that you're not closer to me as I'd love to try my control unit in your car and (all of) your units in my car. I'm just concerned that's there's some really bizarre reason* that a new, genuine unit doesn't cure. Without a known, working unit you don't have much choice though.

* I'm thinking along the lines of the two thin wires that go to the control unit. One supplies the working voltage for the unit (presumably 12v - 14v) and the other is the controlling signal for the unit.

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Re: Citroen C5 X7 mk3 climate control heater fan fault

Post by Y Cymro »

Paul-R wrote:
20 Apr 2019, 20:11
It's a shame that you're not closer to me as I'd love to try my control unit in your car and (all of) your units in my car. I'm just concerned that's there's some really bizarre reason* that a new, genuine unit doesn't cure. Without a known, working unit you don't have much choice though.

* I'm thinking along the lines of the two thin wires that go to the control unit. One supplies the working voltage for the unit (presumably 12v - 14v) and the other is the controlling signal for the unit.


Thanks for the offer Paul. I’ve ordered a new unit using Marc’s link and it will be delivered on Wednesday. I agree it’s strange that two new units didn’t work, but they both exhibited exactly the same characteristics as each other, though slightly different to my original unit - on which the fan can be switched off. Perhaps the cheap replacements will work with a C3 or C4 if the characteristics of the controlling sensors are slightly different to my C5 (or they could both just be rubbish!).

I don’t know what signal to expect on the two remaining lines of the control unit. As you say, being Canbus I assume one carries some sort of pulsed signal which I’d be unable to measure with a multimeter.

Anyway, I’ll update this thread as soon as the new unit arrives. With so much practice I can swap them in less than a minute in complete darkness lol.

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Re: Citroen C5 X7 mk3 climate control heater fan fault

Post by Paul-R »

As the wires are not a twisted pair I don't think they're data carriers. I think one of them probably carries a variable analogue voltage level. Could (easily) be wrong though. BTW I don't count a pulsed signal (pulse width modulation) signal as data.

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Re: Citroen C5 X7 mk3 climate control heater fan fault

Post by GiveMeABreak »

The 4 pin connector to the HMCM: No CAN connections on this particular circuit.
X7 HMCM.PNG
X7 HMCM.PNG (6.28 KiB) Viewed 218 times
Pin 2 > Wire 5 = Multifunction motor ECU F5-2 power relay output
Pin 3 > Wire 3 = Multifunction motor ECU F21 main relay output
Pin 4 > Wire 2 = Multifunction motor ECU F1 main relay output
Pin 3 > Wire 4 = Multifunction motor ECU F5-1 power relay output

Wire 5 goes to the A/C ECU on the dashboard.
Wire 3 goes to a Body earth and the BSI
Wire 2 goes to both the Blower Motor itself and also to the Engine Fusebox
Wire 4 goes to the Blower Motor (Earth)

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Re: Citroen C5 X7 mk3 climate control heater fan fault

Post by Y Cymro »

Deleted - double posted
Last edited by Y Cymro on 24 Apr 2019, 20:19, edited 2 times in total.

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Re: Citroen C5 X7 mk3 climate control heater fan fault

Post by Y Cymro »

The Hella/Behr control unit arrived today and I’m pleased to report that my heater is now working perfectly.
For future reference, with the faulty control unit the heater fan blew at a single speed which couldn’t be adjusted using the heater controls. Bridging the heavy cables at the control unit plug proved that the fan could blow at full speed. I bought and tested a £20 Chinese unit from an eBay seller which proved to have the same symptoms though the fan speed was lower. He sent a replacement that was the same. The Hella unit from Amazon was £40 and works perfectly. I could have saved a lot of time spent under the dash by buying the Hella one first.
https://www.amazon.co.uk/5DS-351-320-01 ... ay&sr=8-12

My thanks to all who responded to my call for help, and especially Marc and Paul for their expertise.
Last edited by Y Cymro on 24 Apr 2019, 21:16, edited 1 time in total.