1994 / L E300 Diesel W124 Estate Cabin Heater Problem

[MarkTabs]

To anyone who might be able to help:

In any position out of OFF, the heater on my 1994/L E300 Diesel W124 estate supplies only fully hot air. There is no 'inbetween', it's either 'off' (no heat), with the rotary fan speed heater selector in the OFF (0) position, or fully hot with the rotary fan speed (0/./I/II/III) selector in any position out of OFF and the blue/white/red temperature selector in any position.

Any help would be appreciated!

Thanks,

Mark

 

[jberks]

As I understand it, the common cause for this is either the interior temp sensor in the roof console or the duovalve. The temp control wheel is interior temp - not heater temp as in other cars, so basically either the car thinks its cold inside irrespective of setting and actual temp, or else it can't shut the flow to the matrix off when it is suposed to. I don't know the exact details but the haynes should cover it.

 

[mjtray]

2nd the opinion on the duo valves.....they can get a sticky connection and do benefit from a bit of cave man maintenance, ie a clout to the side with a hammer....not too hard mind!

It can be enough to release the sticky connector internally within the duo valve....thankfully worked on mine.

Alternatively, it could be that the circuit board on the back of the dials has failed, which is also a known W124 weakness.