E300D - no heat from heater

crt

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Having just driven 300 hundred miles in our 1995 E300D without heat I would be keen to know where to start looking.

There's no heat at all on either side at any setting, just cool air. The fan(s) work at the various settings but just belt out cold air.

Is there a thermostat that sticks or otherwise goes wrong or other common fault to look for?

Thanks.
 
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crt

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Thanks for the prompt reply. How do I diagnose which of these it might be, and if the pump is it a quick and easy repair/replacement (thinking of the return journey without heat).
 

television

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You should be able to feel the pump if it is running,,give it a whack it just be the brushes sticking on it..

A meter would tell you if 12 volts are going to it
 
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crt

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And pump 140 is buried behind the dash or is it accessible from the engine compartment (I'm a long way from my manuals at the moment)?
 

television

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It must be under the bonnet as it is sited before the duo valve and that is under the bonnet
 

Bolide

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The Duovalve on an E300 Diesel is unique to that model. The pump is right next to it and they're by the fusebox

Nick Froome
www.w124.co.uk
 
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crt

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Thanks, Nick. I will have a look later.
 
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crt

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I've found what appears to be the pump and duo valve, as Nick says, hard by the fuse box. I've given both parts a tap with a hammer but no change.

There's no warmth in the pipes running up to the units so I assume they're not pumping/opening, unless there's a blockage elsewhere.

What is the next step (after I've checked the voltage which I'll do later). Remove and replace or is there any way they can be further checked in situ?

If I have to remove and replace, how do I get them out as there is very little space and no obvious fixings?
 

television

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Just a thought is the water level OK in the system
 
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crt

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Water level is a bit low but there is still water in the reservoir. I'll top up and see what happens.
 

fullmeister

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I've just replaced my duovalve a really straightforward operation. Three jubilee clips , the electrical conector on the topand a little gentle persuasion . There is a thread about how to strip and repair these. I tried and the internal windings were well beyond repair.
10 quid from a Polish scrappy or 200 from the dealer .....
The auxilliary water pump is even easier to change. Enjoy !
 

47p2

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Remember not to overfill the reservoir
 
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crt

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Ok, topping up the reservoir made no difference.

If I take off the pump and put 12v through it, is it good if it runs and bad if it doesn't. (I can't tell with the engine running if it the pump is running). Or is the test just to replace it with a known good one? (Which I suppose might not be the case if I get a scrap one).
 

television

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Disconnecting the output hose would tell you if it was running, but just with the ignition on you would feel if the pump was working,,you could put a screwdriver blade on the pump with your ear to the handle,

Could the control unit have failed keeping the duo valve closed. Pulling out the electric plug on the valve would prove this point,,as before the valves normally fail in the hot open mode
 

Bolide

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You should be able to feel the pump start running as you turn on the ignition

Also you should be able to feel the Duovalve go from one end of its travel to the other. Turn the heater controls to full hot & turn the ignition on with one hand on the Duovalve. Do the same with the controls on full cold. One way round you should feel a pulse

Nick Froome
www.w124.co.uk
 
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crt

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Thanks for all that.

The pump is working (shown using a screwdriver stethoscope as suggested above).

No change (i.e., still cold) with the duovalves electrically disconnected, but I couldn't detect a pulse as suggested by Nick.

If it isn't the duovalves or the pump, could it be a blocked heater matrix or, e.g., an airlock?

If the matrix, other postings suggest this is a difficult job to extract to flush out - correct?
 

television

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We have had a few post where the matrix was blocked. I can give you all details if this is the case.

I wonder if you could reverse flow the water through the matrix
 

deanb

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Hi guys,

Would be very interested to hear theories on unblocking a matrix

I'm having this exact same problem with my 230te, the duovalve appears to be working as I have heat in the pipes on both sides of the unit...unfortunately It's using about 1/2 pint of water a week so I've got a horrible feeling that the matrix may be busted...or worse the head...

can someone tell me, is the pump before or after the duovalve on the 230te?

Cheers guys!
 
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crt

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Malcolm

Now I'm home I've had a good look at what I've got.

There is 12v going to the duovalves, and the pump is working. I've still not been able to detect a pulse when doing the test suggested by Nick.

There is no heat at the pipe going into the recirculating pump and no heat on the other side of the duovalves.

I have at least least three pipes going into/coming out of the duo valves, plus one blocked off.

The two pipes underneath the duovalves look to be the outlet to the matrix (left and right).

There are two outlets on the topside of the duovalves, going towards the bulkhead at divergent angles. One is blanked off. The other I disconnected. When connected it indicates water movement if the pipe into the recirculating pump is squeezed. I assume this is some sort of bypass and connects back to the pump feed. When this pipe is disconnected, nothing comes out of the outlet. However, when I squeeze the pump inlet pipe, water comes out of the disconnected pipe. When I backflushed the disconnected pipe it immediately filled the main reservoir and caused it to overflow.

I have had to top up the main reservoir periodically over the last year which suggests a leak somewhere.

Your notes on how to deal with the matrix would be appreciated.

Thanks.
 


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