crt
Senior Member
- Joined
- Apr 22, 2005
- Messages
- 137
- Reaction score
- 10
- Your Mercedes
- '95 E300D estate, '16 Golf, '58 Unimog 404, '95 Defender CSW
After some years of stability my ‘95 E300D’s heating system is playing up again. Last time, having messed around with the duos repeatedly, replaced the heater matrix (having the dash out twice!) and everything else I could think of with lots of help in this and other forums, I think it turned out to be a stubborn airlock causing the system to run cold in the car. Solution then was was to park nose up hill and run the car while squeezing the top hose. A miracle.
Now, I’ve got heat only on the passenger side. Duo valves stripped, cleaned and top gaskets replaced (using the trick of boring out 20mm tap washers which is what I did last time). Still no driver’s side heat.
Taking out the chinese hat pin valves at the bottom of the duos does give constant warmth both sides, but not piping hot as it should be.
Both sides of the duo audibly click when the connector is attached or 12 volts put across the pins.
I have 13 volts at the duo centre pin when the engine is running. If I then take a wire to earth from the pin either side and turn the corresponding contoller in the car, the passenger side varies by about 1 volt, the driver’s side doesn’t change. This leads me to conclude there is a fault on the driver’s side controller, but possibly a wire fault as well or instead of. A new (used) controller is on its way. So we will see.
But this rigmarole, as well as bringing back bad memories, has prompted me to think about how the duo valves work. As I understand it from this forum and elsewhere, the duo switches to cold when energised. This is, I think, because the coil shoots the top part of the valve downwards and this in turn compresses the bottom, chinese hat part, into the gasket at the bottom meaning no hot water comes through. But is this right? In my duos the chinese hat part does not seem to have sufficient travel to be compressed, ie it seems it would still be floating when the top part is down. Furthermore, if as is claimed, the valves fail in hot mode, how can this happen if the top part of the valve is, due to the spring, closely held against the top gasket when at rest (ie un-energised). How does the hot water get through to the bottom part of the valve?
As for the electrics, am I right in assuming that the constant +12ish v at the centre pin makes a circuit through the pin either side to the respective controller to earth? Meaning that the rheostat controller in the dash is effectively controlling resistance to earth? Or is something else happening with that centre pin voltage?
I am really interested to know what people think.
Thanks.
Now, I’ve got heat only on the passenger side. Duo valves stripped, cleaned and top gaskets replaced (using the trick of boring out 20mm tap washers which is what I did last time). Still no driver’s side heat.
Taking out the chinese hat pin valves at the bottom of the duos does give constant warmth both sides, but not piping hot as it should be.
Both sides of the duo audibly click when the connector is attached or 12 volts put across the pins.
I have 13 volts at the duo centre pin when the engine is running. If I then take a wire to earth from the pin either side and turn the corresponding contoller in the car, the passenger side varies by about 1 volt, the driver’s side doesn’t change. This leads me to conclude there is a fault on the driver’s side controller, but possibly a wire fault as well or instead of. A new (used) controller is on its way. So we will see.
But this rigmarole, as well as bringing back bad memories, has prompted me to think about how the duo valves work. As I understand it from this forum and elsewhere, the duo switches to cold when energised. This is, I think, because the coil shoots the top part of the valve downwards and this in turn compresses the bottom, chinese hat part, into the gasket at the bottom meaning no hot water comes through. But is this right? In my duos the chinese hat part does not seem to have sufficient travel to be compressed, ie it seems it would still be floating when the top part is down. Furthermore, if as is claimed, the valves fail in hot mode, how can this happen if the top part of the valve is, due to the spring, closely held against the top gasket when at rest (ie un-energised). How does the hot water get through to the bottom part of the valve?
As for the electrics, am I right in assuming that the constant +12ish v at the centre pin makes a circuit through the pin either side to the respective controller to earth? Meaning that the rheostat controller in the dash is effectively controlling resistance to earth? Or is something else happening with that centre pin voltage?
I am really interested to know what people think.
Thanks.
