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SLK 250cdi R172 2012
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10 Posts
Discussion Starter #1
Hi All, I have an R172 250cdi that has decided not to heat the cabin. car owned 10 months and this issue is new.

Blower fan is working and the redirects to feet, face or screen are working but the temperature is consistently tepid regardless of heater setting. Coolant level is good.

I searched around a bit and got lots of hits regarding heater control valves but could only find information for R170/171. Does the R172 have these also? I also found info on actuators on the HVAC system that might be an issue.

Does anyone have any suggestions on the issue, and where to find the offending/broken bits?

Thanks,
Alex.
 

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SLK 250cdi R172 2012
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10 Posts
Discussion Starter #3
Thank you, and for sure lots of comments but most or all related to R171 or SL55 or similar - none related to the standard R172 as far as I can see. Certainly the useful PDF in the SLK R172 discussion seem to be R171. I could be mistaken of course.

Does anyone know if the R172 actually has these duo valves? and if they exist, where are they located?
 

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Registered 2012 SLK250
2012 SLK 250CDI
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402 Posts
Hi All, I have an R172 250cdi that has decided not to heat the cabin. car owned 10 months and this issue is new.

Blower fan is working and the redirects to feet, face or screen are working but the temperature is consistently tepid regardless of heater setting. Coolant level is good.

I searched around a bit and got lots of hits regarding heater control valves but could only find information for R170/171. Does the R172 have these also? I also found info on actuators on the HVAC system that might be an issue.

Does anyone have any suggestions on the issue, and where to find the offending/broken bits?

Thanks,
Alex.
I sometimes have the same problem but the other way around, start a warm engine and I get blasted by intense heat regardless of temperature setting.
If I turn the AC on it goes back to normal within 20-30 seconds, something that controls the heating system is AWOL but with the easy fix I have not bothered to fix it. Might be worth turning the AC on and off just to see what happens!
 

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* Registered
SLK 250cdi R172 2012
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10 Posts
Discussion Starter #7
I sometimes have the same problem but the other way around, start a warm engine and I get blasted by intense heat regardless of temperature setting.
If I turn the AC on it goes back to normal within 20-30 seconds, something that controls the heating system is AWOL but with the easy fix I have not bothered to fix it. Might be worth turning the AC on and off just to see what happens!
Thanks. I have tried playing with the AC on/off and heater hot/cold. Every possible combination!
 

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SLK 250cdi R172 2012
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10 Posts
Discussion Starter #8
No valve, there is a coolant circulation pump by the coolant reservior, also verify the function of the blend flap actuator.

Sent from my SM-G781U using Tapatalk
Thank you. Is the blend flap actuator the one accessible through the glove box?
 

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SLK 250cdi R172 2012
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10 Posts
Discussion Starter #10
If I remember correctly it's through the tunnel carpeting.

Sent from my SM-G781U using Tapatalk
I got a bit further today. The problem is the air blend system, the motor throws a "mechanical fault" from the actuator. I took the motor/actuator off and it will drive each way dependent upon temperature demand but the the flap itself is stuck fast (cold position I assume) meaning the motor won't drive it.

Any thoughts on the next step?
 

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Registered 2014 SLK350
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545 Posts
Sure sounds like the flap has an obstruction...can you move it by hand? Maybe an object in the way or it needs some lubrication.
 

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Registered 2012 SLK350
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950 Posts
Yes mechanical fault is indicated when the actual mechanism has a problem. If you cannot losen it from the outside you'll have to remove dash and open the heater case.

Sent from my SM-G781U using Tapatalk
 

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* Registered
SLK 250cdi R172 2012
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10 Posts
Discussion Starter #13
Yes mechanical fault is indicated when the actual mechanism has a problem. If you cannot losen it from the outside you'll have to remove dash and open the heater case.

Sent from my SM-G781U using Tapatalk
Thanks. I took the actuator off and then tried to twist the spline but it wouldn't move. Does the whole dash need to come off?
 

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Registered 2012 SLK350
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950 Posts
Yes, luckily since it's a convertible it's somewhat easier.

Sent from my SM-G781U using Tapatalk
 

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Registered 2013 SLK200
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49 Posts
I've got exactly the same problem. The local specialist replaced the blend flap motor and it was OK for several months. The fault has now resurfaced. It looks as though somethings binding up.

Is there any way of viewing the flap without taking the dash apart?
 

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Registered 2013 SLK200
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49 Posts
Went out to the car today after the most terrible storm overnight. I plugged in my reader and looked at the live data stream for the climate control. Started her up and played with the temperature control to make the blend flap move.

The problem appears to have resolved itself, yesterday it was jammed on hot and then on cold, With the code reader monitoring the flap it would only get to 35%. Today it merrily cycles between 0% and 100% and maintains the temperature properly. It does quietly tick as it moves but I think it always did do that. I left the car running for about half an hour while I looked at various readings and fiddled the temperature up and down. I couldn't get it to fail.

Maybe I will have to run the car once a week to keep everything free.
 

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* Registered
SLK 250cdi R172 2012
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10 Posts
Discussion Starter #17
Went out to the car today after the most terrible storm overnight. I plugged in my reader and looked at the live data stream for the climate control. Started her up and played with the temperature control to make the blend flap move.

The problem appears to have resolved itself, yesterday it was jammed on hot and then on cold, With the code reader monitoring the flap it would only get to 35%. Today it merrily cycles between 0% and 100% and maintains the temperature properly. It does quietly tick as it moves but I think it always did do that. I left the car running for about half an hour while I looked at various readings and fiddled the temperature up and down. I couldn't get it to fail.

Maybe I will have to run the car once a week to keep everything free.
Frequent use is probably a good idea! I'm going to pretend my problem has disappeared for a while and then find some time to take another look. As far as I can see there is no way to inspect the flap mechanism itself without some major surgery - meaning warmer and drier days as I cannot put it in my garage (that is full of motorcycles).
 

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Registered 2013 SLK55 AMG
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539 Posts
looks like I might have a similar problem. No temperate at all from the heater in whatever setting. Service and MOT due next month but the main stealer wants £194 just to diagnose the issue. I know I get that back if I get it repaired but I'm not prepared to gamble that it might not be an excessively expensive repair.
 

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* Registered
SLK 250cdi R172 2012
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10 Posts
Discussion Starter #19
looks like I might have a similar problem. No temperate at all from the heater in whatever setting. Service and MOT due next month but the main stealer wants £194 just to diagnose the issue. I know I get that back if I get it repaired but I'm not prepared to gamble that it might not be an excessively expensive repair.
£194 sounds expensive just to investigate, however many service outlets charge £100 just to plug in the OBD system.

I have mine booked into an an independent service garage who reported they had fixed this exact same issue recently but they have to take out the whole heater box for the repair. Dashboard off completely so around 10 hours of labour. £600 to fix the issue but no choice and I need it to work.
 

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Registered 2013 SLK55 AMG
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539 Posts
£194 sounds expensive just to investigate, however many service outlets charge £100 just to plug in the OBD system.
Luckily I swapped main dealers after the first one left me a voice message saying that the time and date I booked on their system was not actually available and if I still wanted a service to ring them back. I can understand errors - the time slot and date not being available but poor customer service to just leave a voice message and throw the ball back in my court I thought, so I've gone elsewhere (still main dealer). They will, for £90 (an hours work) investigate and think they should be able to find the issue in that time (probably by plugging in the OBD as you say). I will find out on 1st Feb - if it's £600 to fix like yours I'll be ok with that, anymore than that kind of price and I'll not bother and just wear thermal underwear in the winter !!
 
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