Climate control problems following screen replacement

[Mac209]

CLK 350 (W209) Convertible, 2006, Following windscreen replacement the vehicle’s ‘climate control’ (Thermatic) malfunctions when the ‘auto’ setting is selected (and once engine coolant is heated) - it:

- increases cabin fan-speed to ‘quite high’ within a few moments after selecting ‘auto’ with no control of fan speed (except ‘off’ when ‘0’ is selected on rotary dial).

- pumps out hot air into cabin (with no apparent control of temperature via the usual rotary temperature dials).

- Turning off ‘auto’ stops high fan speed but cabin air temperature is not controlled and stays hot - even when manually using the rotary temperature dials.

I suspect possible malfunction of one of the 2 cabin temperature sensors… The sensor that I suspect is in this light cluster which (of course) has to be purchased as a complete unit - i.e. the sensor is not replaceable by itself... (photo attached).

At the same time, my Indie garage checked for fault codes (he cleared them all only last week) and suddenly 'found' 4 pages of 'faults' showing of which only the seat heater was 'real' and needed to be reset. The battery was not disconnected during the windscreen change.

Please, if any 'guru' can throw any light on this most annoying problem I would be grateful.

 

[mattkh]

What do the people who changed the windscreen suggest?
On my old A class, there is a very quiet fan inside the bit in your photograph. Can you feel a draught over there?

 

[Mac209]

What do the people who changed the windscreen suggest?
On my old A class, there is a very quiet fan inside the bit in your photograph. Can you feel a draught over there?

Unhelpfully, they say “not our problem” unless I can prove otherwise. The gentle draught you mention is the airstream being pulled over the upper temperature sensor - which I can not detect right now. So I’m searching for a replacement rather than paying MB’s new parts price which I fear is north of £300!

 

[Mac209]

I have just changed the screen-mounted sensor pack containing the rain sensor and auto-on headlight unit as a forum member suggested this could be the source of the problem. The old one (removed) has something which rattles in the casing and is also missing the 25mm long heating resistor that is present and visible on the new one. No change to my climate control problem unfortunately... But maybe there are fault codes that still need clearing before anything changes. I'm now looking to acquire a replacement interior light unit containing the upper temperature sensor. What a endless waste of time and effort. May end up going to the local MB dealer and paying for a diagnostic and getting a quote to do the work.

 

[alexanderfoti]

Is everything connected? Lots of things won't generate a fault code when disconnected, especially internal components. A check of the actual values of both the upper control panel and the climate ecu may help point you in a better direction.

Additionally, being a convertible, the upper sensor is switched in and out depending on if the roof is up or down.

 

[Mac209]

Is everything connected? Lots of things won't generate a fault code when disconnected, especially internal components. A check of the actual values of both the upper control panel and the climate ecu may help point you in a better direction.

Additionally, being a convertible, the upper sensor is switched in and out depending on if the roof is up or down.

Thanks for replying Alex. As far as I'm aware "everything" is connected. As mentioned in my original post "my Indie garage checked for fault codes when I initially went to him with this problem (he cleared them - a couple of 'trivial' ones only the previous week) and suddenly 'found' 4 pages (!!) of 'faults' showing - of which only the seat heater was 'real' and needed to be reset. The battery was not disconnected during the windscreen change." At that time he mentioned that it was possible that I have had a rear-SAM problem but everything I read about faults there suggest it would show up in rear-end faults which I don't have.

I will mention your suggestion to him when I next go. I'm awaiting a replacement 'upper control panel' (the interior light cluster by the mirror) as I'm suspicious that a wire break there could produce totally random faults (plus replacing it should validate the upper temp sensor operation). He doesn't have a Merc STAR Analyser but has a friend locally with one maybe this would check the values to which you refer.

 

[Flyinspanner]

Yes, getting it on star is probably a very good idea - hopefully the bloke who has it knows the system.
Sounds like your “indie” is just a general garage .... maybe you should find an MB specialist indie - they usually have great in depth knowledge of the marque - which can actually save a bundle on guessing it may be “X” or “Y” where you end up changing parts that are actually not at fault.

(the - yeah we changed that, and think that there’s another fault......)

hope you fix it

 

[Mac209]

Yes, getting it on star is probably a very good idea - hopefully the bloke who has it knows the system.
Sounds like your “indie” is just a general garage .... maybe you should find an MB specialist indie - they usually have great in depth knowledge of the marque - which can actually save a bundle on guessing it may be “X” or “Y” where you end up changing parts that are actually not at fault.

(the - yeah we changed that, and think that there’s another fault......)

hope you fix it

That’s sound advice. I have used this guy for 6 years and he has been very good for all general service. Yes, the costs are mounting up slowly but I will see if I can find a more specialist guy locally.

 

[Flyinspanner]

Post up where you live/work and you may get a recommendation

 

[Mac209]

Post up where you live/work and you may get a recommendation

Done. Weymouth, Dorset. Thanks for the suggestion.

 

[Frontstep]

Could this not be a faulty temperature sensor that is mounted in the header at the top of the windshield in the light assembly.

Someone with star should find it before chucking parts at it.

 

[Mac209]

Could this not be a faulty temperature sensor that is mounted in the header at the top of the windshield in the light assembly.

Someone with star should find it before chucking parts at it.

That's what I suspect but have not got firm evidence yet. Have booked STAR diagnostic for this Thursday. Also waiting on a 2nd hand light assembly to arrive (cheap at £25 when the new MB part is £295 quoted today!!). Going to try to pin this down... Thanks for your reply.

 

[Frontstep]

Hopefully at that price your part will arrive and cure it.

 

[Mac209]

Hopefully at that price your part will arrive and cure it.

Finally resolved! Went back to an Indie MB specialist with a STAR (or better?) who ran full tests including temperature sensors readings (thanks Frontstep) which showed complete 'blank data' from the upper temp sensor. Removed and disassembled upper light unit with tiny sensor in front of internal fan which showed that the sensor-mounted wire was broken hence no readings from there. Only solution was to order new interior light unit (£295...) which will come in 7-10 days and then, hopefully, "end of story". Thanks for your helpful thoughts fellow forum members.

 

[Frontstep]

Finally resolved! Went back to an Indie MB specialist with a STAR (or better?) who ran full tests including temperature sensors readings (thanks Frontstep) which showed complete 'blank data' from the upper temp sensor. Removed and disassembled upper light unit with tiny sensor in front of internal fan which showed that the sensor-mounted wire was broken hence no readings from there. Only solution was to order new interior light unit (£295...) which will come in 7-10 days and then, hopefully, "end of story". Thanks for your helpful thoughts fellow forum members.

Good news,

a picture of the offending broken part for us inquisitive ones would be good, especially if a component can be identified.

 

[Mac209]

Good news,

a picture of the offending broken part for us inquisitive ones would be good, especially if a component can be identified.

I’ll retain the old one and photo the PCB with fan in place and post it.

 

[davemercedes]

Finally resolved! Went back to an Indie MB specialist with a STAR (or better?) who ran full tests including temperature sensors readings (thanks Frontstep) which showed complete 'blank data' from the upper temp sensor. Removed and disassembled upper light unit with tiny sensor in front of internal fan which showed that the sensor-mounted wire was broken hence no readings from there. Only solution was to order new interior light unit (£295...) which will come in 7-10 days and then, hopefully, "end of story". Thanks for your helpful thoughts fellow forum members.

Congrats on finding that - sounds like the proverbial needle in a haystack! It's a shame you couldn't re-join the broken wire but even if you could, everything like this is always so tight it would probably break again when installing!

 

[Mac209]

Congrats on finding that - sounds like the proverbial needle in a haystack! It's a shame you couldn't re-join the broken wire but even if you could, everything like this is always so tight it would probably break again when installing!

It’s more like a filament (in a bulb) than a wire so rejoining it wasn’t feasible. Plus I imagine that soldering it could easily change the resistance characteristics and thus mess up the working anyway! I’m just going to suck up the cost and look forward to it working properly again! (Fingers crossed!)

 

[Mac209]

(Seem to have lost the text...) New overhead light / sensor assembly fitted today and heating now works properly. As promised I attach pictures of the:
- Light assembly
- PCB from inside the assembly - note the 'sniffer fan' on the top left
- Detail of the 'sniffer fan' showing the broken filament wire and the tiny sensor on it
The assembly needed to be coded to the car so not just 'plug and play'.

Final thoughts:
- There are so many different variations of the light assembly. At one stage I got one that was apparently identical (from outside) but was not fitted with the 'sniffer fan' and thus useless.
- The PCB showed minute traces of corrosion possibly caused by drizzle / rain getting pulled into the assembly when the soft top had been down and the weather 'turned' - why the XYZ the PCB wasn't varnished seems shortsighted by MB.

 

[joderest]

oh why do cars need this sort of thing ????????
My ML270 heating system has been crap since i have owned it, sometimes selects screen, other times it does not.
Now it will either blow hot or cold, nothing in between, and seems its all linked to outside temperature, as sometimes goes cold with out touching dial, turn up heat a bit and it goes hot again.
I like just a simple heating system, and believe me if it was possible to convert it to that, i would.