E300D heater blowing cold

[crt]

I'm at a loss with what to do with my '95 E330D estate's heating system.

It started blowing cold whatever the heating control setting a couple of weeks ago. The engine runs at about 80 degrees as normal.

The duovalves are working, although I've stripped them down twice. I've flushed through the heating circuit twice with a hose until it ran clean (after the first time, I had heat briefly). The recirculating pump is also working.

The pipe taking the water feed from the engine side to what I think must the heater matrix is hot. The pipes either side of the duovalves remain cold.

I took the top off the duovalve when the engine was hot and revved the engine. Water pumped through the duovalves, but it was cold, even though the engine side was hot. This suggests the heater matrix is not blocked but I might not be fully understanding the heater architecture.

Does anyone have any idea about what might be going on here or where I might next look?

Thanks.

 

[Mercedes cozy]

take out the pins in the duo valve and then try the car.

 

[N7OGP]

do these have a sensor next to the interior mirror which determines the hot/cold.

 

[ACID]

hi

Change the duovalves common problem

acid

 

[bolide]

Non-a/c, a/c or climate control?

Nick Froome

 

[crt]

Thanks for all those suggestions.

I've taken the pins out of the duo valves and it made no difference. When the engine is hot, and I took the top half of the duo valves off, only cold water came through from the heater matrix side when I revved the engine, so I am not sure it can be a duo valve problem as it seems that there is no hot coming through at all from the engine side.

I think there is a sensor next to the interior light/sun roof controls, but could this affect the heating system if there is no heat at all reaching the duo valves - I thought that sensor operated the duo valves via the main heating controls. (In what I thought was a separate development the sunroof fuse keeps blowing - could there be something wrong in the area of the sensor and the sunroof control area?)

It is an air con model.

One of the many of the puzzling aspects to this problem is that I had heat temporarily after I first flushed out the heating loop, and then it became erratic, I seemed to be losing a lot of water (apparently from somewhere on the left hand side of the engine compartment - i.e., where the hot water comes out of the engine before the heating loop) and the engine temperature rose rapidly. I now have no heat at again, and also no apparent water loss and a steady 80 degrees on the gauge.

 

[Mercedes cozy]

Your water pump may have gone, hence over heating and no water circulating.

Thanks for all those suggestions.

I've taken the pins out of the duo valves and it made no difference. When the engine is hot, and I took the top half of the duo valves off, only cold water came through from the heater matrix side when I revved the engine, so I am not sure it can be a duo valve problem as it seems that there is no hot coming through at all from the engine side.

I think there is a sensor next to the interior light/sun roof controls, but could this affect the heating system if there is no heat at all reaching the duo valves - I thought that sensor operated the duo valves via the main heating controls. (In what I thought was a separate development the sunroof fuse keeps blowing - could there be something wrong in the area of the sensor and the sunroof control area?)

It is an air con model.

One of the many of the puzzling aspects to this problem is that I had heat temporarily after I first flushed out the heating loop, and then it became erratic, I seemed to be losing a lot of water (apparently from somewhere on the left hand side of the engine compartment - i.e., where the hot water comes out of the engine before the heating loop) and the engine temperature rose rapidly. I now have no heat at again, and also no apparent water loss and a steady 80 degrees on the gauge.

 

[crt]

Would a water pump failure be sporadic? I'm no longer overheating or losing water, but still do not have heat in the cabin.

 

[crt]

Some years on and doing some bits and pieces on the old merc reminded me of this thread. I fixed the problem eventually: it was a stubborn airlock in the system which I cleared by following a method recommended on one of the US sites: park nose up hill, flush through the big radiator hose with a hosepipe while constantly squeezing the hoses, which seems to operate to push the airlock up and out. Though not before I had the dash out and replaced the heat exchanger from the heater, leaving me with a perfectly servicable spare heat exchanger if ever I need one.

 

[Codger49]

All credit to you for posting up the resolution, but nearly 8 years must be a record.


PS You forgot to mark the thread as 'solved'.