W203 - Climatic blowing warm air even when set to cold

[cws196]

On my W203 the vents are blowing warm air on all but the minimum temp setting. I've tried doing the blower vents-reset (to no avail) and will be getting a diagnostic done mid-week, but what I have been told is that it's likely one of 2 sensors - either the temp sensor housed behind the vent in the interior light control panel on the roof-lining or the temp sensor housed behind the vent in the Climatic control panel.

Just wondered if anyone else has had a similar issue and if it was something other than the above?

 

[Neil Mackay]

Have you got dual digital control!? If you have press and hold rest until the screen changes to show 01 etc: The two sensors you are talking about are, I believe, 00 and 01. On the opposite side of the screen will show the temperature those sensors are reading and the control panel will take the average of them to set the blower speed and temp. 02 is the outside temp sensor! My climate doesn't feel that hot at the vent but both those sensors will be reading virtually the temp the panel is set at!

Plus I've found that Mercedes climate control to ease you upto or down to a temp rather than blast that temperature at you immediately!

 

[cws196]

No, the car is Climatic as opposded to Climatronic (think that's right) so dials with no digital display/no ability to do self-diagnosis.

I can feel a definate difference and it has got worse over the past month.

 

[Neil Mackay]

Have to say I'm interested in the result you get once plugged in! When mine is set to "auto" it's useless just blows luke warm regardless! I've looked at the ambient temp (which is the same sensor that shows the external temp on the instruments) and this morning the dash said 6c and when moving slowly and then parking the air con diagnostic of the same sensor said 40c...........but the dash still said 6c.......

 

[lexman8]

this morning the dash said 6c and when moving slowly and then parking the air con diagnostic of the same sensor said 40c...........but the dash still said 6c.......

Strange as it sounds, both figures are 'correct'.

Because the external temperature sensor detects excess heat from the engine when the car is stationary, the dash continues to display the last 'valid' temperature from when the car was moving. I don't know what the trigger speed is but I'd guess 10 mph?

I believe most Mercs work this way; mine certainly does.

 

[Neil Mackay]

Strange as it sounds, both figures are 'correct'. Because the external temperature sensor detects excess heat from the engine when the car is stationary, the dash continues to display the last 'valid' temperature from when the car was moving. I don't know what the trigger speed is but I'd guess 10 mph? I believe most Mercs work this way; mine certainly does.

That is strangely logical! Mine will need to be plugged in as in auto, like the OP, blows luke warm no matter what it's set too

 

[lexman8]

Neil - Have you checked the left and right heater core temperatures (parameters 03 and 04) when in diagnostic mode? This might indicate whether the duo valve is working okay.

Also, fyi, 05 is the evaporator core temperature, 06 engine coolant temperature, 07 refrigerant pressure and 08 refrigerant temperature. As you may have noticed there are scores of other parameters.

Have you checked the error log for the climate system? To display it ensure that both controls are set to Auto and press the REST and Charcoal Filter buttons together for more than 5 secs. You can then step through any logged error codes using the right temperature button. I have a list of about 40 or 50 error codes. Each is of the form Bxxxx where xxxx is a 4 digit numeric code; eg, B1417 is left heater valve fault.

If you don't have a charcoal button there'll be some other way of accessing the error list so you may have to Google it.

 

[Neil Mackay]

Neil - Have you checked the left and right heater core temperatures (parameters 03 and 04) when in diagnostic mode? This might indicate whether the duo valve is working okay. Also, fyi, 05 is the evaporator core temperature, 06 engine coolant temperature, 07 refrigerant pressure and 08 refrigerant temperature. As you may have noticed there are scores of other parameters. Have you checked the error log for the climate system? To display it ensure that both controls are set to Auto and press the REST and Charcoal Filter buttons together for more than 5 secs. You can then step through any logged error codes using the right temperature button. I have a list of about 40 or 50 error codes. Each is of the form Bxxxx where xxxx is a 4 digit numeric code; eg, B1417 is left heater valve fault. If you don't have a charcoal button there'll be some other way of accessing the error list so you may have to Google it.

Hi, yes checked those and both are the same as the engine coolant temp! I've got blend flaps on mine not a duo valve and there is no fault diagnostic option on my unit

 

[gazz]

I saw a W211 E class last week where the outside temperature sensor had failed, showing +85 deg C, and the heater was blowing warm all the time. Fitted a new sensor to the front bumper and the heater magically resolved itself. Interestingly, my Star would communicate with the climate control unit, would show live data, but when asked for fault codes would return "no communication". With the sensor replaced fault codes could be read again - "no fault codes" stored.

 

[Neil Mackay]

Mines just random! Some days it works some days it doesn't! It's not blown hot hot for ages and if you start at 16 and gradually increase the temperature it will get warmer to say 25 degrees then get colder again as you go upto hi! Mines had a replacement control panel though so Olly thinks it may need a star coding to my car (it came from an 03 US C320 rather than a C32) if I could be bothered Id put the old unit back in and see if that blows hot (only changed it as the display pixilated)

 

[gazz]

It might benefit from a normalisation proceedure. You may be able to do this with a combination of button holds. Basically moves all the motors from one end stop to the other and back, like a calibration proceedure.

 

[Neil Mackay]

It might benefit from a normalisation proceedure. You may be able to do this with a combination of button holds. Basically moves all the motors from one end stop to the other and back, like a calibration proceedure.

Yeah I've tried that! From what I understand from across the pond we may have different P1 and P2 information coded in the unit

 

[Neil Mackay]

It might benefit from a normalisation proceedure. You may be able to do this with a combination of button holds. Basically moves all the motors from one end stop to the other and back, like a calibration proceedure.

Had a 40 minute diagnostic session my HVAC today......result was the drivers footwell flap that was supposedly repaired 6 weeks ago is still stiff or broken......!!!

 

[Starky]

Any update on this Neil? Who carried out the repair?

 

[Neil Mackay]

Any update on this Neil? Who carried out the repair?

A company called Hampshire Service centre! Went back and ended up having to have the footwell motor replaced too! It's better but not what id say perfect mainly as the charcoal flaps been unplugged by a previous owner so it will never reset properly!

 

[deanfirst]

anyone tried to top up the freon? or 134a?

 

[Braaast]

On my W203 the vents are blowing warm air on all but the minimum temp setting. I've tried doing the blower vents-reset (to no avail) and will be getting a diagnostic done mid-week, but what I have been told is that it's likely one of 2 sensors - either the temp sensor housed behind the vent in the interior light control panel on the roof-lining or the temp sensor housed behind the vent in the Climatic control panel.

Just wondered if anyone else has had a similar issue and if it was something other than the above?

Hey cws196 same issue here on my C230 and it got worse the faster I go.. My Merc guy did not find any issue with STAR (no fault) and say it could be mechanic.
Have you solved the issue on yours? I know it's been a few years, you might not have the car anymore. (especially if it's got the M272 engine..)

 

[cws196]

Hi - sold the car over a year ago but what I can say is that the problem went away without having to do anything. I also never found any fault codes.

 

[Braaast]

Hi - sold the car over a year ago but what I can say is that the problem went away without having to do anything. I also never found any fault codes.

No worries, thanks for responding