L322 Rear heater control

Hi all, rear temperature blend flap appears not to be working, no fault codes registered.
Blend flap position stats at 0%, as does every other value related to rear temperature status.
If the rear climate control button is turned off (on by default) then hit air stats blowing from the rear vents.

Any ideas where to start? I'd rather not take the entire car apart to find a duff fuse etc but i don't know where to start.

I really don't know, but have a read see if it helps.


J

Thanks. That's actually really helpful. Few more things to test, watch this space...
I've confirmed that there's only one cabin temp sensor and that's working properly.

Ok i pressed the defrost button, which should shut off the rear face vents.
The rear climate control button turned off but i could still feel some blow from the rear face vents. Wonder if that's a smoking gun?

Well a small update, there's never any blow, either not or cold from the rear under seat vents.
With the rear climate control button turned on (orange light) there the rest fan speed dial works and for her the desired flow rate from the rear face vents.
Turn the rear climate control button off and there is now zero flow to all rear vents

I wonder if it's worth trying the old.. turn it off and on again trick? Disconnect the battery for a while?

Is there anything explained in the manual kermmmz

Well more unexpected progress.. the blow control started working properly tonight, at least for part of the journey, as did the auto setting.. fan speed and distribution actually worked automatically!! Still nothing from the rear feet vents though

That means any issues i may or may not have are intermittent.. i wonder is that a bad hevac ecu?

Mark Piercy said:

Is there anything explained in the manual kermmmz

Click to expand...

The pages @marjon has kindly shared give pointers but without any error codes I'm feeling in the dark

kermit_rr said:

Well more unexpected progress.. the blow control started working properly tonight, at least for part of the journey, as did the auto setting.. fan speed and distribution actually worked automatically!! Still nothing from the rear feet vents though

That means any issues i may or may not have are intermittent.. i wonder is that a bad hevac ecu?

Click to expand...

Much more likely to be connector problems.

Datatek said:

Much more likely to be connector problems.

Click to expand...

I like that answer and i hate that answer!! I'm guessing it will be hard to find/fix the dodgy connections and mean taking half the interior out to reach the actual heater attempt which has all the blend/distortion motors

I think I have found a couple more docs, that may do yea head in or help .

Anyway your getting em.

J

marjon said:

I think I have found a couple more docs, that may do yea head in or help .

Anyway your getting em.

J

Click to expand...

Thanks! I see the aux coolant pump is to maintain flow at low engine speed.
I've noticed the cabin can cool down at idle, i wonder if that's something else that's not working all the time? It must work sometimes because the fbh works pre-startup

Problem is the heating and ventilation crosses over and joins in with the climate control and the pre heat part.

I did not read the docs in total, but it does confirm your assumption of where the cabin temp sensor is.

J

Summit like this might solve your issue @kermit_rr
Needs altering to suit specific scenarios though.

Flossie said:

Summit like this might solve your issue @kermit_rr
Needs altering to suit specific scenarios though.View attachment 304661

Click to expand...

Still don't get any blow to the rear!! Ooerr missus!!

Done some more digging, some of it unrelated and things start to add up, if you're an optimistic counter
I've not been able to extract a valid ccf file. This can have all sorts of miscellaneous symptoms, including;
Dodgy cruise control CHECK
Dodgy hevac CHECK

Diag (sdd) is sure my car has a dpf, it's obvious it's been gutted.. causes of a dodgy ccf include writing a new file (to map out the dpf and who knows what else) without sufficient voltage (this wouldn't surprise me)

I'm wondering i if all of this is tied together...

I wonder if it's part of the reason my mpg counter is so far off?