W203 windscreen demist boost

[Palfrem]

On my 2006 C280 when I switch the windscreen blower / demist button on, the aircon and auto lights go out.

This means that soon every window is steamed up.

In every other MB the aircon has stayed on and it has routed all the blower up the windscreen.

My local MB dealer seemed not to know what it is supposed to do this morning.
Two chaps gave me both options as the "right" one.

It's under AUC warranty so I'm keen to know what's what.

They were supposed to have checked it today when they fixed some front suspension problems but no-one had looked at it when I came to collect the car.

Any ideas chaps? Thanks

 

[craig1912]

My W204 does the same thing-I set the fan on full whack and manually set thendirection.

 

[Rory]

On my 2006 C280 when I switch the windscreen blower / demist button on, the aircon and auto lights go out.

I'm pretty sure that's how it is on my car too. But MB have messed with the meaning of the a/c light over the years - in my car, the light being off means the a/c is on.

 

[WOODYTHEWISE]

Hi, its strange, on mine, light on,a/c is off. Its a bugger when a MB dealer does not know.

 

[markjay]

Hi, its strange, on mine, light on,a/c is off. Its a bugger when a MB dealer does not know.

Same here. A/C light (red) goes off, front windscreen demist light (amber) goes on, and I get full blast of cold aircon air directed to the front windscreen, demisting it in seconds.

When I turn the front windscreen demistoff, the front windscreen demist light (amber) goes off, but the A/C light (red) stays on until I switch it off (if I want to).

 

[markjay]

On my 2006 C280 when I switch the windscreen blower / demist button on, the aircon and auto lights go out.

That sounds about right.

This means that soon every window is steamed up.

That does not.

In every other MB the aircon has stayed on and it has routed all the blower up the windscreen.

And that is right again....

 

[whitenemesis]

This is for the Thermotronic unit but function is pretty much the same for the Thermatic

 

[whitenemesis]

Sorry post #7 should have read this is for the Thermatic, Thermotronic is much the same

 

[corned]

Sounds like you may need to get Dyno-rod in to clear the aircon unit drain tubes. The moist air is not getting dried out properly, and then being blown around the interior, condensing back on the windows?

 

[GP801]

On our CLK it stays on. On the SLK goes off. It seems illogical to turn the a/c off when you want full demisting power.

 

[GP801]

Just a thought but we had a 203 that always had moisture on the windows. Turned out after much head scratching at the dealers that some parts were installed the wrong way roundand it was recirculating the same air all the time.

 

[Palfrem]

WHITENEMEIS - That's perfect, thank you.

Back to MB then I suspect

 

[Rory]

I'm pretty sure that's how it is on my car too. But MB have messed with the meaning of the a/c light over the years - in my car, the light being off means the a/c is on.

Ah, there we go from whitenemesis' post - they changed the a/c button function:

"Display logic of function LED in the AC button (7)

For vehicles up to 31.5.05, the function LED is off when the compressor is on.

For vehicles as of 1.6.05, the function LED is on when the refrigerant compressor is on.


For the OP's problem, could it be that the outside temp is too low for the a/c to work?

 

[Palfrem]

Rory - Should the aircon not dry the air regardless of temp?

 

[Ted]

No, the cooling part turns off below a certain temperature as the water would turn to ice on the evaporator.

 

[whitenemesis]

Refrigerant compressor switches off when the evaporator temp reaches 2c

 

[fatdazza]

Does this mean that if the evaporator temp reaches 2c, that the blowers will not "demist" the windscreen as effectively because it is not blowing dry air?

On a frosty morning when I start up, the misty windscreen seems to take a while to clear - is this the cause?

 

[whitenemesis]

That is how I understand it. I share your experience of a slow demist on very cold starts.

 

[Rory]

I know many people say leave the a/c on all the time, but I turn it off when not needed. The trouble with the MB system (typical of all "prestige cars") is the a/c doesn't turn off immediately so the trick of shutting it off a few mins from home to dry out the system doesn't work. So you start up the next morning and all the wetness in the system gets dumped straight into the car. If it's too cold for the a/c to work you've had it.