E-Class (E300 TD) W210 Heater Control Problems

[rjsdavis]

Hi all - I've been spending some considerable time trying to resolve a heater control problem - with no luck. I have just replaced the duovalve, and this has made no difference!

I have spent more time testing the system, and have discovered that when the car is driven from cold, and the heater fan is set to "0", only ambient air comes into the cabin, which gets progressively warmer as the engine does. If I leave the vents open - nothing particularly comes into the cabin for the first 35 mins.

After 35-40 mins, things get worse. I have the EC button switched on, as currently I have no refrigerant in the a/c system, so there's no point in running the air-con system. I am simply trying to fix the heater problem at the moment. After 35-40 mins, the heater fan starts to operate, and blows HOT air into the cabin. If I leave the vents closed, I can soon start to feel the centre console getting warmer and warmer, as the hot air is simply circulating around inside the centre console of the car.

If I open the vents to let the air in the car, I can feel that the volume of air is the equivalent to the heater fan being set to about 1.5 or 2.0 on the main control panel. Also - the EC button red light comes on, which indicates that the fan is operating. The EC red light does not come on for the first 35 mins or so, so I can deduce that for some reason - the heating system appears to want to turn itself on. This happens every day, and after about the same amount of time each time!

The temperature of the air is the same (hot) irrespective of whether the temp controls are fully red or fully blue.

Therefore, I am not sure what to do next. I have tried pulling off the duovalve cable as you suggested, and it made no difference at all. This thing is really frustrating me!

 

[jberks]

Ok - back to basics - when the heatyer is on cold, as I understand it, there should be 12v at the duovalve - is there?
If so, the duovalve should close and there will be no hot air in the cabin.
If there is 0v, then the duovalve is set to hot irrespective (default).
Next check the fuses. I assume you'll have 0v.
From memory, the way it works is that the power starts at the heater controls, runs through the ambient temp sensor and then out to the duovalve.
So, all things being equal, the ambient temp sensor and fan would be my next port of call.
What I don't get is the heater fan. This should run as per the control, irrespective of anything else. Does it?

 

[rjsdavis]

Thank you so much for your helpful reply. I will check the voltage at the duovalve and let you know how I get on...... I will also try to identify which of the fuses controls this, and check that also....

In terms of the fan - this is curious. It works in exactly the way as I described in the original post. It is extremely consistent, and turns itself on (to approximately level 1) without any user changes.

The fan itself appears to funtion normally, when the user DOES turn it on. It gets progressively more powerful as you turn the dial round to 5.

What I have noticed is that after the fan has turned itself on, and the user turns the fan on anway - you can hear that at each stage the fan gets quicker, UNTIL you get to stage 4, at which point the two notches between 4 and 5, don't appear to make any difference - it's as if, because the fan is already functioning with the dial set to zero, the system gets to it's maximum speed two notches earlier.

I shall let you know how I get on with the voltage test on the duovalve....

 

[rjsdavis]

Ok - back to basics - when the heatyer is on cold, as I understand it, there should be 12v at the duovalve - is there?
If so, the duovalve should close and there will be no hot air in the cabin.
If there is 0v, then the duovalve is set to hot irrespective (default).
Next check the fuses. I assume you'll have 0v.
From memory, the way it works is that the power starts at the heater controls, runs through the ambient temp sensor and then out to the duovalve.
So, all things being equal, the ambient temp sensor and fan would be my next port of call.
What I don't get is the heater fan. This should run as per the control, irrespective of anything else. Does it?

Thanks again for the reply - I've had my mechanic look at it, whilst he was sorting out my gearbox thump (which incidentally is the gearbox mount) - I helped him to test it, and can confirm that when both of the temp controls are set to max cold - there is 12.8v coming through at the end of the plug that powers the duovalve....

When the temp controls are set to max hot, it drops slightly to 11.7v - but is still very much active. Therefore - I'm at a slight loss - as if there is 12v coming through all the time - then surely there should be no hot coming through at all?? Or does it work the other way round that 0v = max cold, 12v - max hot, and the valves are closed until opened by the current???

I am really trying to work out whether it's my duovale (which is a new one from a breaker!), or something else - I'm pulling my hair out!!!!

 

[Dosco]

Being very new to the Owners Forum I have just read this one and I have a similar problem, which is: - When I turn the blower rotary switch to the off position it does not seem to switch off totally in that it becomes intermettent and I can hear (and see the RED ECON light flashing) what seems like a relay rapidly "dropping in and out" or perhaps better described as "relay chatter" The noise comes from under the glove box and the fan is working very slowly as one would expect on the slowest/lowest setting during this happening.

Would this be due to the heater speed control as described by answers to this thread or is it more likely to be the rotary fan control switch, if the latter how on earth do I change it, more importantly, source a replacement other than the MB spares centre.

Many thanks in anticipation.

 

[rjsdavis]

I've made some small progress with my heater fan coming on all on it's own....

It used to come on regular as clockwork after about 45 mins driving - in a similar way to Dosco above - however, in frustration - I whacked the dashboard whilst driving - and it immediately turned off. A few miles later, and after hitting a pothole, it came back on again. Again - another whack on the dash turned it off again - and so and so on - so this was progress, as at least I was able to stop the hot air from blowing in.

However, the other day - it came on AGAIN, and I really whacked the dash. It has never come again since, so I can only assume that there is a loose connection or other problem with the heater control panel itself. I was striking the dash to the left of the instrument cluster and to the right on the passenger airbag.....

It still works perfectly properly, when you actually turn in on with the fan control knob - it just doesn't turn itself on by itself anymore - unfortunately - hitting the dash didn't control the temperature problem!!!

If in doubt - smack it with a hammer.....

 

[robertspycher]

ambient temp sensor

Hi All, I have the same problem and I will perform jberks tests.
On the other hand can someone tell me where to find the ambient temp sensor on the E300 1999.
Would most appreciate your help. Pls send me the answer to info@inqbos.com
Thanks a lot.

 

[jberks]

Hi All, I have the same problem and I will perform jberks tests.
On the other hand can someone tell me where to find the ambient temp sensor on the E300 1999.
Would most appreciate your help. Pls send me the answer to info@inqbos.com
Thanks a lot.

From memory its in the roof light unit.

 

[television]

AS jberks in the OCP

 

[robertspycher]

Thanks to all. Although I don't know what the term OCP means. Sorry for my English.
Robert

 

[television]

Thanks to all. Although I don't know what the term OCP means. Sorry for my English.
Robert

Overhead control panel

 

[robertspycher]

Thanks to all.

 

[robertspycher]

Does any one have a Overhead control panel disable/ensemble (or a spare parts drawing) procedure to share?
Thanks