alan.cockell

Can anyone please advise me on how to cure the following.

My E300D blows hot air irrespective of where either of the the controls are set.

Martin_T

I have exactly the same problem. And nothing happends when i push the EC and Recirkulation button. Not even the lamps on the button goes on.
Do yours also do like this?
Mine is a E220 1993.

shdoug

I would suspect the heater Mono valve staying open. It's located by the battery. It could also be many other things, such as a failed temperature sensor, located above the rear view mirror by the sunroof switch. Or a bad setpoint potentiometer. Or failed controller.

If everything else in the system works correctly, (fan speed changes with setpoint, dampers transition, AC compressor runs) then I would direct attention to the Mono valve or the blending damper under the dash (not fun). the mono valve is by far the easiest to fix.

shdoug

I would suspect the recirc switch or its wiring.

Martin_T

Where can I locate it? Is it the switch in the panel? None of the 3 buttons work...

shdoug

The plot thickens...

E220? Is yours a European model with the dual zone control and 2 selector knobs? If so, I'm not familiar with that control system. If the entire system is dead I would start checking/wiggling fuses around.

Martin_T

Yes, it is an european version.
All the other function works properly.
I've checked the fuses and they are all ok.
There is a very small fusebox beside the big one. In the small fusebox there is only one fuse, but there is room for two. What will happen if I put another fuse in there?

the1beard

W124 Heater help.



A faulty Aux pump will not affect the lh or rh temp.

If one side is not working then it's going to be one of the following
1.Duo (stuck)
or
2.sensor (either faulty “unlikely” or disconnected which can happen if the carstereo /cd is messed with)
or
3.the controller panel (fairy likely please see my test procedure below)
or
4.a broken wire between one of the above. (least likely but possible as thesecars get older.)





There are three sensors one in the roof area and two in the fanenclosure one for LH and one RH if either one of the LH or RH sensors becomedisconnected then that side will only give out full heat. (this can happen whenfitting a stereo head unit and tugging cables)

If you want to check yours it's behind the control unit you will need to removethe control unit and the switch panel above (this is fairly awkward I did it byremoving the LH switch and the rear cable cover which you will need to remove by flipping it over) then push the switchpanel back until it unclips move it to the left behind the clip allowing it tocome forward and it will then be able hang to the left.

The sensors are almost directly behind each LH and RH control dials.

They are inserted into the plastic matrix housing and the connector is a push fitthere is one for each side.

Compared the resistance with of each sensor to see if one is at fault.

Also if the connection to the duo valve is removed the heater will blow hot sothis is another simple duo valve test.



If there is heating on only one side another simple test of theduo valve to rule it out is to switch the wiring this will then tell you if itthe duo valve or the control unit with the dials.



To do this disconnect the electrical connector it has three connectionsthe middle one being the earth (do not connect any of them together onlyconnect back to the duo valve) using three cables with ideally with crocodileclips reverse the LH and RH connections to the duo valve keeping the centre connectorconnected to the centre connector on the duo valve.

Then using the heating control inside the car see if the problemis reversed LH to RH or RH to LH.
If it is then the control panel is faulty. It may be possible to strip andclean the contacts on some versions.



If not then it’s likely to be the duo valve. It may be possible to strip and fix some versions.

This test works on A/c and non A/c cars