Climate Control problems following screen replacement

[Automac29]

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.

 

[Kerabo]

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.

Hello
not yet. I bought a top light like in the picture but there are so many different ones. I have it to fit but don’t hold much hope? just had an operation so out of action for a while. I also have the lower controls but have put it somewhere and can’t find it.
I have a horrid feeling that when I done a heater reset that one flap may have suck, I hope not but will see.
please post if you learn anything.

 

[MrGreedy]

There might be a UV loading sensor behind the windscreen near the rear view mirror. If the screen has just had a generic one chucked in, the bulk screen company might not have calibrated the sensors to compensate for the new screen. Always get Merc to replace the screens would be the common advice on this forum. Windscreen replacement via insurance (if this is the route you went) will cover this, but you need to push for it.

I don't know where you stand if you have already 'accepted' whatever was chucked in...

I say accepted, but you might have trusted 'professionals' to know what they are doing and do a good job...

I say professionals, but I mean the stack em high sell em cheap generic volume windscreen replacement badgers who can't deal with anything except the simplist of jobs, and even then, have been known to mess that up.

 

[MrGreedy]

If you have access to diagnostics, like iCarsoft Pro, you can interrogate the data/readout for all the temperature and UV sensors, and see if any of them are giving obviously weird readings.

 

[Automac29]

There might be a UV loading sensor behind the windscreen near the rear view mirror. If the screen has just had a generic one chucked in, the bulk screen company might not have calibrated the sensors to compensate for the new screen. Always get Merc to replace the screens would be the common advice on this forum. Windscreen replacement via insurance (if this is the route you went) will cover this, but you need to push for it.

I don't know where you stand if you have already 'accepted' whatever was chucked in...

I say accepted, but you might have trusted 'professionals' to know what they are doing and do a good job...

I say professionals, but I mean the stack em high sell em cheap generic volume windscreen replacement badgers who can't deal with anything except the simplist of jobs, and even then, have been known to mess that up.

Yes it was Nationwide Motor Glass (SAGA's official go-to supplier) who did the replacement and it is a 'generic screen'. The installer (said he has 20 years in the trade) returned to examine the job with me right beside him and could find no evident wire break or visible damage. He swears that all he had to do was unclip the rain/headlight sensor from behind the damaged screen and clip it back to the new one - no disconnections needed. Ther headlights come on fine and rain sensor (always a bit strange) works as normal. Being a 2006 car I don't think there's anything to calibrate and nothing my Indie MB man has suggested. Bottom line (at the time) was a £75 excess payment to them vs £550+ from Autoglass and heaven knows how much from a local MB dealer...

 

[Automac29]

If you have access to diagnostics, like iCarsoft Pro, you can interrogate the data/readout for all the temperature and UV sensors, and see if any of them are giving obviously weird readings.

My Indie MB man has a couple of good diagnostic machines which currently can not find a specific problem. Next step (when I replace the central overhead light cluster with the top climate sensor inside) will be to go to 'his mate' nearby who has a MB Star diagnostic reader which apparently can delve deeper into the systems.

 

[MrGreedy]

My Indie MB man has a couple of good diagnostic machines which currently can not find a specific problem. Next step (when I replace the central overhead light cluster with the top climate sensor inside) will be to go to 'his mate' nearby who has a MB Star diagnostic reader which apparently can delve deeper into the systems.

Hi, you're response on what has been checked is not clear.

Has the garage just done a read for any fault codes; or,

Have they looked at all the temp related sensor readout when the car is running to see if anything looks odd e.g. a temperature showing an inconceivable temperature? Which would indicate a faulty sensor, but might not throw an error code?

I was advocating the latter, but it will take 5 mins in the car checking the data, which might be more than some can be bothered with during 'fault finding'.

 

[Gbrowncls55]

Does the high speed fan that you cant control blow everywhere ie can you still choose where the air comes from or is it just the front screen.

 

[sgregory124]

If you have access to diagnostics, like iCarsoft Pro, you can interrogate the data/readout for all the temperature and UV sensors, and see if any of them are giving obviously weird readings.

I agree with this. I had a Alpina D3 that needed a new windscreen, which also contained one of the sunlight sensors. The sensor was faulty and the climate control was all over the place, they came back and switched the sensor, job done. I'd get the windscreen people back before you do anything else.

 

[Automac29]

Hi, you're response on what has been checked is not clear.

Has the garage just done a read for any fault codes; or,

Have they looked at all the temp related sensor readout when the car is running to see if anything looks odd e.g. a temperature showing an inconceivable temperature? Which would indicate a faulty sensor, but might not throw an error code?

I was advocating the latter, but it will take 5 mins in the car checking the data, which might be more than some can be bothered with during 'fault finding'.

So far the work done has been reading through fault codes and clearing whatever shows one by one, then running the car and rechecking for any recurrence. So, “no”, no sensor readouts t my knowledge. Maybe this is what he has in mind by taking e car to his chum’s Star analyser. To date he has been diligent and I am paying his time.

 

[Automac29]

Does the high speed fan that you cant control blow everywhere ie can you still choose where the air comes from or is it just the front screen.

Oddly it appears to be directed at the front screen only, I think from the slotted vents at the screen base. I can hear the flaps move when I synchronise them (holding recirc and fast screen clear buttons together) so had not made any sense of that. But you are right, I have not been able to change air direction as I would have expected.

 

[Automac29]

I agree with this. I had a Alpina D3 that needed a new windscreen, which also contained one of the sunlight sensors. The sensor was faulty and the climate control was all over the place, they came back and switched the sensor, job done. I'd get the windscreen people back before you do anything else.

When the fitter returned he unclipped the sensor (no disconnection) to have a look at it. Oddly rocking the sensor module produced a rattle... Maybe a change of sensor would be a good next move. Thanks for your info.

 

[Automac29]

I agree with this. I had a Alpina D3 that needed a new windscreen, which also contained one of the sunlight sensors. The sensor was faulty and the climate control was all over the place, they came back and switched the sensor, job done. I'd get the windscreen people back before you do anything else.

I have changed the screen-mounted sensor pack containing the rain sensor and auto-on headlight unit. 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.

 

[Gbrowncls55]

it sounds to me then that for some reason you are stuck on front screen demist, which on mine I think disables the other functions until its switched off. Sadly why this maybe i have no idea ...faulty switch, sensor etc. what happens when you turn the front demister switch on and off?

 

[Automac29]

it sounds to me then that for some reason you are stuck on front screen demist, which on mine I think disables the other functions until its switched off. Sadly why this maybe i have no idea ...faulty switch, sensor etc. what happens when you turn the front demister switch on and off?

No, I checked this again a short while ago when I replaced the rain sensor. Happily that front screen demist works fine (I need it when I cannot otherwise control clearing the screen). The only other 'oddball' is when I perform a synchronise of the air ducts (press that demist and recirc buttons together and watch their LEDs flash alternately) the process ends with the red recirc button LED remaining lit which I wonder if it is highlighting a fault.

 

[whitenemesis]

You need to get the car on STAR. Sometimes the a/c reset can only be completed using STAR.
Also you can get the codes read and stop guessing what's wrong.

 

[Automac29]

You need to get the car on STAR. Sometimes the a/c reset can only be completed using STAR.
Also you can get the codes read and stop guessing what's wrong.

Yes, I think that you are completely right. What initially seemed to be a 'silly' fault that 'must' have an easy fix has become a tedious time waster. I have been exceedingly wary of involving the MB dealer (purely for 'fears' of cost in my retirement) but either the other Indie with a STAR, or failing that, the dealer - but getting a quote after paying the dealer diagnosis. Appreciate your reply.

 

[Automac29]

Finally resolved! Went back to an Indie MB specialist with a STAR (or better?) who ran full tests including temperature sensors readings (thanks MrGreedy) 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.

 

[Gbrowncls55]

I had the same on my wifes r230. not possible to just replace the sensor so as above had to buy a whole new inerior light unit. Solved the problem though

 

[MrGreedy]

Glad it looks like your there. It's a shame garages don't use even modest fault finding to track this sort of thing down. If you lived up in the Midlands, I would have volunteered to use my iCarsoft pro and just have a look at the data. The iCarsoft was on a group buy from this forum in the past 12 months (£150-200 range I think) and it literally takes 5 minutes max to look at all climate sensor readouts.

My view is that if a garage hasn't invested in a decent fault scanner for a few hundred quid and can't figure out to look at this sort of thing, I couldn't trust them with most jobs. Except maybe hitting things with hammers.


I'm not a mechanical/car expert by any means; I've just tinkered with my car for a few simple bits and pieces here and there, and take time to learn. My amateur skills, knowledge and equipment should ALWAYS be eclipsed by people doing this as their profession.