Cabin heater is useless in my CLK 2.7 diesel, please help.

[reggie musson]

My lovely 2004 CLK 2.7 diesel has the worst heater I have ever had in any of my last 27 cars I have previosly owned.
I have had the thermostat changed so the tempature does reach around 90 degrees after 20 minutes driving, but on a frosty morning the windscreen will only demist halfway up untill the engine is fully warmed up, yes, at least 20 minutes.
I leave the air con on all the time and even try the demist button, but all this does is to light up a little red light on the button but does not demist the windscreen.
I understand the engine is all made of iron, but this is not what I would expect from an up market car.
My last car , a diesel Jaguar had a great heater so can`t understand why the CLK is so poor.
Is this just my motor or has anyone out there with the same problem ????

Reggie

 

[andy27168]

Hi,
Have you got a decent flow of air out of your vents?
You could have a blocked cabin/pollen filter(s), it often gets missed in servicing.
Had similar issues with my C230k and a new filter solved it.
Very easy to do and filter was cheap in the case of my car.

 

[jaymanek]

could be the duo valve needs looking at..

Or a more common issue is your pollen filter is blocked? Are you getting gale force wind when you hit the demist button? If not then its your filter.

 

[Alex Crow]

No duovalve on a 209 Jay.

This car should have an electrical heater booster to aid demisting from cold in winter. Sadly they often fail.
Another feature that helps is the EGR flow through the cooler.

 

[reggie musson]

Thanks Andy and Jay, will check out the pollen filter as there is very little air coming out the heater vents, just need to find the filter, any ideas ?
I have heard of the heater booster Alex but how can you check its working ? You also mention an EGR flow through the cooler helps but don`t know what this is.

Big thank you to all for replying. I was thinking of selling the car just because of this problem as I live in the sticks and just gets that bit colder here.

Reggie

 

[AJA]

I had a similar problem on my wife's car and I removed the pollen filter completely. She doesn't want it replacing as the car demists so quickly now. The air flow is immense now.

 

[reggie musson]

Have replaced the pollen filter today thanks to all the advice from you all, and the flow of air has improved. Be interesting how quick or slow it takes to demist now.
I wonder if the electric heater boost is working, as I suspect its not and expect it will cost hundreds to fix.
Reggie

 

[reggie musson]

I had a similar problem on my wife's car and I removed the pollen filter completely. She doesn't want it replacing as the car demists so quickly now. The air flow is immense now.

Is your wife`s car a diesel.
Shame they dont have a filter for the winter months that lets more air through, after all what is the point of a pollen filter in the winter as there not any pollen about ?

Reggie

 

[Alex Crow]

The EGR (exhaust gas recirculation) cooler uses engine coolant to lower the temperature of the EGR gas before it enters the combustion chamber. One handy knock on effect of this process is faster heating of the coolant, which is obviously used for heating the inside of the car and demisting the screen. We might assume the EGR system is working fine, you might expect poor performance or warning lights on the dash otherwise.

The heater booster is mounted on the engine block, and at low ambient and engine temps is used to boost the heating of the coolant to aid demisting etc.
This is an item that does regularly fail, and will not give any tell tale signs, other than slow heating of coolant, and poor demisting from cold.
It is easy to test with diagnostic equipment, but would be hard to DIY test.

 

[Rory]

I have heard of the heater booster Alex but how can you check its working ?

On my 2004 C Class the heater booster has to be enabled in the cluster computer. I think it can be set to 'on', 'off' or 'off with a/c button' (something like that, anyway).

Once it's set then it should work automatically at 8C or below. I *think* the car has to be moving for it to work though, as it takes such a great electrical load - I believe it's 1.7KW. Certainly in my car, warm air comes through within 30 seconds of driving.


I note you said you leave the a/c on all the time. The snag I find with this is if the temp is around freezing then the a/c won't work (to prevent the evaporator from freezing) so if the system is wet from the previous day's use, it's just dumping that wetness into the car. In a Mercedes, you can't do the trick of turning off the a/c a few mins from home to dry the system out either, as it takes 10-15mins to go off fully.

 

[davidjpowell]

Sounds daft but did they definately change the thermostat?

 

[whitenemesis]

On my 2004 C Class the heater booster has to be enabled in the cluster computer. I think it can be set to 'on', 'off' or 'off with a/c button' (something like that, anyway).

Once it's set then it should work automatically at 8C or below. I *think* the car has to be moving for it to work though, as it takes such a great electrical load - I believe it's 1.7KW. Certainly in my car, warm air comes through within 30 seconds of driving...................................

The booster heater will only take current once all other consumers are satisfied and I believe that includes the battery recharge from starting the car.

 

[Michael_]

On my 2004 C Class the heater booster has to be enabled in the cluster computer. I think it can be set to 'on', 'off' or 'off with a/c button' (something like that, anyway).

Once it's set then it should work automatically at 8C or below. I *think* the car has to be moving for it to work though, as it takes such a great electrical load - I believe it's 1.7KW. Certainly in my car, warm air comes through within 30 seconds of .....

Automatic, off and off with air con. Just checked on mine. Doesn't appear my heater booster works either! Always wondered what that meant or did!

 

[Rory]

Sounds daft but did they definately change the thermostat?

If it's eventually getting up to 90, then that's fine. Actually the OP says it does that after 20mins - he doesn't say what kind of driving. but that doesn't sound too bad at all, especially in colder weather.

 

[Rory]

Automatic, off and off with air con. Just checked on mine. Doesn't appear my heater booster works either! Always wondered what that meant or did!

Do you have yours set to auto?

 

[reggie musson]

Sounds daft but did they definately change the thermostat?

Yes the thermostat was changed.

 

[reggie musson]

If it's eventually getting up to 90, then that's fine. Actually the OP says it does that after 20mins - he doesn't say what kind of driving. but that doesn't sound too bad at all, especially in colder weather.

Most of my driving is on rural country roads, with the 60 speed limit.

 

[reggie musson]

The air flow has improved on to the screen and demist has improved a little after changing the pollen filter, but very little air flow if any when I switch from demist to the other cabin vents, as it was before. I was wondering if I had a blockage somewhere.

Reggie

 

[whitenemesis]

Very little air will come out of other vents until there is sufficient heat in the coolant when the a/c is set to auto. Demist will over-ride this and force air flow, whatever the temp.
Have you tried with the a/c on manual, setting the blower speed manually?

 

[Alex Crow]

There is a second thermostat on this car, munted on the front of the condenser, behind the horns.
It can also slow down engine heating from cold, and will probably not be expensive to replace.

One more thing, I had a CLK320 in this very week with poor air flow through the passenger side vents when on hot settings - this affected ALL pass side vents. The airflow on driver's side was good on hot or cold, and pass side was fine on cold. This pointed to a fault with flap control on the pass side - one of the control linkages had hopped out and needed replacing, all is well now.