S211 intermittent HVAC fan

[plastic]

The heater fan in my 2009 S211 has begun to play up in the past few months. When starting the car from cold, the fan runs as normal blowing air, but then will shut off for a seemingly random period. The control panel seems to have no effect on bringing it back to life, then magically after an unknown period of time it'll come back. This may repeat itself a couple of times, before settling down and working normally for the rest of the journey (as long as the journey is > 30 minutes long, it seems).

The temperature coming from the vents is exactly what it should be so I guess it isn't the duo valve at fault here.

I've replaced the fan itself and tried a new resistor, however neither cured the issue.

I've since followed the diagnosis guide on Pelicanparts, connecting an oscilloscope to the connector coming from the HVAC control panel and can see that indeed the control signal does appear to die and return at random.

Has anyone experienced such a fault before? Am tempted to get a HVAC control panel from ebay and give it a go, though there appear to be many versions of them!

 

[plastic]

Well a new HVAC control panel didn't make a difference... I am a bit stumped here now. What other components are even involved? Perhaps some temperature sensors?

 

[MJJ]

Attached below are the various sensors that are used by the HVAC system to make control decisions. If you have a diagnostics tool like iCarsoft, you will be able to track the live data for these parameters to hopefully see where it is going wrong.

When you over-ride the Auto setting on the control panel, and set fan speed and temp manually, do you see more normal fan behaviour - either at the fan itself, or via the oscilloscope trace at the control panel connector? I am reading your first post as saying that manual over-ride has no effect, and that is indeed strange behaviour - thinking aloud here, perhaps the aircon refrigerant is getting very low and cooling performance is borderline - thus, after some minutes of high fan speed to cool the car, the evaporator temperature gets too warm and the HVAC slows the fan to allow evap temp to further cool.

Martin.

 

[plastic]

Hi Martin, thanks for the attachments I'll give them a good read through - clearly much more intelligent than I thought it was!
In response to your question - no, when overriding the Auto and manually setting the fan at any speed, it still doesn't function. Regarding the aircon refrigerant, I fitted a new condenser last year and re-gassed. The AC blows ice cold (when the fan works!) when set to a cold enough temperature so am not that's an issue.

I will see if I can get an icarsoft - I have a feeling it must be an excessively high (or low) reading of a sensor that is causing the cut out...

 

[plastic]

I bought a MaxiECU and have just retrieved some data - will post the XML output in a bit.

Indeed the blower regulator temperature appears to shoot up to 215C occasionally and 25V voltage which coincides with the fan stopping (assume some sort of protection system from the climatronic head unit). When it works, the regulator temperature is 25C and 14V voltage.

So it seems that the blower regulator is bad, yet I've tried 3 separate replacements (2 x Mahle Behr branded ones and 1 x second hand one) yet the problem persists.

Suggests the blower regular itself isn't bad, but whatever is detecting & reporting the temperature back to the head unit is bad. What could that be?

 

[plastic]

Just been out for a drive and the fan was doing its usual on/off. It's warm here today so had the AC on, which blew nice and cold when the fan was on. Attached is all the data I collected in the journey from the maxiecu



This chart clearly shows the times when the fan was not running (interior temperature was about 35C initially), started heading down nicely when the fan kicked in, i.e. when the blower regulator temperature was not reported as 215C, but reported as a sensible value of 25C or so.

Really hoping someone can help suggest which part could be the culprit here...!