W124 Duovalve - 1989 300E

[1001ab]

Hi,
Looking for a hand with the duovalve and associated blower controls.
It's a non-AC car.

The air blows hotter than hell in any position other than the very top at the 'MIN'/blue position. I mean when you rotate the roller until it clicks in the highest position at blue, which seems to lock something off.

I attempted the duovalve clean up procedure from the DIY section and it didn't make much difference. Same effect at the controls.

If I disconnect the duovalve completely, attempting to simulate a failure or bad wiring, then I get hotter than hell all the time even at the top of the blue part of the roller.

I think this may rule out the duovalve and I suspect it means that the temp rollers are not connected to anything or something in the heater matrix may have failed.

Any thoughts?
As ever, any help hugely appreciated.

 

[dinoy]

u need to test i have the reverse heating did not work it turned out to be the control unit in the middle of the dash not the due valve, there is somebody locally who recondition it for £80, but i bought 2nd hand from breaker for 30 delivered try robert walker

 

[Dec]

Use a hose clamp on the hose from the water pump to duo valves as a temp solution until you get the bottom of the problem.

Dec

[YOUTUBE HD]NROVVncW8Zc[/YOUTUBE HD]

 

[1001ab]

The hose clamp is a brilliant idea. Never thought of just isolating it like that.

I have spares, I wondered if this ruled out the duovalve but it seems not. I'll get a spare one on and see how it goes.

 

[Dec]

If both sides of the car heating have the same fault then it’s likely that the heater control panel is at fault… any chance this fault is just down to the extremely hot weather at present, maybe things will get back to normal when the weather cool down.

Dec

 

[1001ab]

If both sides of the car heating have the same fault then it’s likely that the heater control panel is at fault… any chance this fault is just down to the extremely hot weather at present, maybe things will get back to normal when the weather cool down.

It's been like this for ages but the super-hot weather has prompted me to have a look at it.
It is the same on both sides so I'll look at changing the heater control panel, I have a non-AC car for spares.

 

[Dec]

What about putting in a stop kock, you could have the first manually operated heating system on a W124.

Dec

PVC Stopcock w Flow Indication 1 4 1 2 ID x 1 4 1 2 ID from Cole-Parmer

 

[1001ab]

We're going on holidays in it tomorrow so I thought I would see if it was something silly.
Probably not the best time to be cutting into the pipework.

 

[optimusprime]

info

Check to see if auxilary coolant pump is working , as it sits on the lower part of engine compartment drivers side .This pump circulates the water for heater. And returns it to the pump. You can test with a 12 volt feed to it.Unbolt it from the body it will give you better view.

 

[kth286]

there is a temp sensor in the overhead light unit.

a little motor and small bore pipe behind the glove box feeds cabin air to it,
and provides the signal to switch heating on/off (higher/lower).

 

[1001ab]

there is a temp sensor in the overhead light unit.

a little motor and small bore pipe behind the glove box feeds cabin air to it,
and provides the signal to switch heating on/off (higher/lower).

That sensor and pipe are definitely disconnected, would that be the problem?

I had no interior light at all in this car for months, only put one back in the other day and didn't reconnect that pipe and whatnot.

I'm on hols just now but can give this a try easily enough.
This would be an embarrassing fix...