New owner with intermittent heater fan issue

[Mark Oldfield]

Hi, I just collected a new to me 2005 W203 C270 CDI estate. It is an old girl with 300,000Km... driving home, it sounds like there is a heater fan on the passenger side that is intermittent on full then off.. It is intermittent.. Can anyone help me out on this? Thanks

 

[Blobcat]

Hello and welcome

 

[Dean Fletcher]

Hello and welcome

 

[Jim2]

Hello and Welcome !!!

 

[John Laidlaw]

Welcome

 

[M80]

Since no one has offered anything,
as a guess could this be a duo valve issue, one side sticking perhaps?

 

[Frontstep]

Hi, I just collected a new to me 2005 W203 C270 CDI estate. It is an old girl with 300,000Km... driving home, it sounds like there is a heater fan on the passenger side that is intermittent on full then off.. It is intermittent.. Can anyone help me out on this? Thanks

Hello it could well be, I would suspect the heater fan resistor first maybe blower motor after,

Of course, check connections first and youtube will have a video on getting to it.

I assume you feel the air blowing through the vents and then not?

 

[Mark Oldfield]

Hello it could well be, I would suspect the heater fan resistor first maybe blower motor after,

Of course, check connections first and youtube will have a video on getting to it.

I assume you feel the air blowing through the vents and then not?

Hi, I can hear it, it sounds like the fan is fitted to the passenger side near where the rear door is hinged??? I'm fairly sure it isn't fitted there though...? It goes from full power to nothing every few seconds but intermittently.

 

[A.J.]

Hi Mark, welcome to the forum.

 

[Frontstep]

Hi, I can hear it, it sounds like the fan is fitted to the passenger side near where the rear door is hinged??? I'm fairly sure it isn't fitted there though...? It goes from full power to nothing every few seconds but intermittently.

Open the bonnet and listen under there for the fan.

Shows location;


https://www.pelicanparts.com/techar...Replacement/BODY-Cabin_Filter_Replacement.htm

 

[Mark Oldfield]

Since no one has offered anything,
as a guess could this be a duo valve issue, one side sticking perhaps?

Hi M80, What is the duo valve?

 

[M80]

Hi M80, What is the duo valve?

Rather than I trying to explain something I have little experience with perhaps you try a google search on 'Mercedes Duo Valve'.
There are various threads on this site to.

But basically as I understand, 2 valves in one block that allow for his and hers independent heating control.

 

[Rory]

There isn't a duo valve on the C Class - it just uses air blending.

I don't use my car much and its fan has stopped working a couple of times, especially just after the car has been started, but then it'll start up again.


Bit of a long shot re the noise coming from the rear - I notice you said 300,000kms; cars for some markets had an additional a/c unit in the rear.

Stick the climate on manual (in my car auto is useless) and direct the air to the face level vents. Shut the vent on top of the dash. The noise and air flow should be pretty even from all the face level vents.

 

[M80]

There isn't a duo valve on the C Class - it just uses air blending.

Didn't not know that,
so there is an air blend flap driven by a motor through gears I expect.
On the Gr Cherokee the gears stripped causing similar if not the same.
I should've been a dash out job but instead I carefully cut the plastic enclosure to gain access to the gears, it being an older mo mo.

 

[Mark Oldfield]

I think I have found the issue... There is an additional independent blower fan in the central console between the front seats supplying the two vents blowing towards the rear seats.. The vent flow control appears to work as a variable switch controlling the fan speed... I cycled it a few times and it seems ok now, so I guess dirty switch contacts were the problem.