Where has all my heat gone

[w201]

Newbie to this forum I have a problem with my heater in the very cold weather.
I have read most of the posts about this it?s not the valve or air locked or the heater matrix.
I have a 190 1991 model the heater is fine most of the time until the weather turns really cold then I loose all the heat when the blower is on speed 3 or four the temp gauge sits normal and there is heat for about 20 secs after switching on the blower if I turn the blower off for 30 secs there is heat again for about 20secs then it goes the heater matrix is new could this be a problem with the insulation on the bulkhead. Thanks in advance.

 

[190]

I have the exact same problem with my car in the cold weather when not so cold heater is excellent. I don?t think anyone on this forum knows I think if it not a light that out or how to clean your car then you must take it to a dealer.

 

[w201]

someone out there must have had this problem before.

 

[landover]

Have you tried a main dealer.

 

[jberks]

Ok guys - no idea of the exact fault - but simple physics - The colder the air/ the faster the fan speed, the faster it will cool down the heater matrix, so it seems to me that the heater matrix is not heating up quickly enough to compensate, effectively meaning that the flow of water through the matrix is not fast enough. I would guess that something is partially blocked (kinked pipe etc - you say the matrix is new so it can't be that) or the water pump isn't as efficient as it once was and it can't push the water through the matrix fast enough any more. Another thought, does the 190 have a water valve before the matrix or is the temp based on cold/hot air mix? Usually this would result in the heater being warm when set to cold, but you never know if its partially blocked or shut.

I can't see what effect the insulation would have, or it would never get hot enough in the first place.

And I doubt the dealer would have a clue - Specialist might though.

 

[panason1c]

Is the engine reaching its full operating temperature?.......could be that you need to replace the cooling system thermostat.

 

[w201]

Thanks for your answer jberks & panasonic there is plenty of flow through the matrix it also has a new water pump fitted the heater control valve is working fine but I do agree with your first point about the colder air was out in the car this morning and the heater was very hot but its not that cold outside it?s as if it?s drawing to much cold air.
The engine temp is also fine between 80-85 going to 90-95 before the fan cuts in will have to investigate further.

 

[cruicky68]

Hi,

I've got a feeling it could be the thermostat. If the water pump and matrix have been replaced and you have good water flow through. I once came accross an old ford with a similar fault, the thermostat was jammed slightly opened. It still seemed to be getting warm as usual albeit slighly slower. Heater would start blowing hot air then quickly became cold. New thermostat cured it. Certainly worth a go as it would be the cheapest option. Hope this helps

 

[jberks]

I had similar issues with a Ford, although in my case the stat itself was fine, but the rubber seal around it had perished, making it irrelevant. Odd, if the matrix is hot, with good flow, you run cold air through and it goes cold, then it infers that the engine temp would drop at the same time. There is a piece of the puzzle missing I imagine.
Daft thought,
the Merc heater is thermostatically controlled, driver/passenger side independent. Do both sides go cold? - Is the ambient temp sensor dicky and closing off the hot air supply as soon as any warm air gets to it?

 

[jberks]

Hi guys,
May need some help with this one. Unless I have the wrong end of the stick, on the W201 and W210 (the only mercs I have personally had so know well enough), there is an "ambient temperature sensor/fan" in the roof light / switch cluster. As the heater seems to work on the same thermostatic principles as my dad's first W123 back in 1979 I presume Merc have always controlled them in a similar way. So, techs out there, where is it, how does it work on the 190 and could it cause the symptoms described if it got very touchy?

 

[william silver]

heater fault

I have just replaced the duovalve - located on the heater circuit before the flow into the heater matrix - on my W124 E320 estate (valve bought discounted from MB Blackpool). My symptoms were that when the heater setting was set to MAX the heater blew hot. When set to any other (lower) temperature e.g. 22, the heater blew cold air. This a default safety setting.

The duovalve is in operation permanently as it responds to the varying temperature input from the cabin temperature sensor. Because of this the water flow is varied - if the duovalve is kaput sufficient water cannot get through to the heater matrix.

I had previously replaced the thermostat as the cheaper first option available but this didn't cure anything.

 

[jberks]

Ok, so the principle is that the duovalve is controlled by the signal from the cabin temp sensor which is located in the roof console, presumably combined with some info from the temp selector switches.

I would guess that the current from the control selectors will be fed through the temp sensor which will increase resistance as the temp rises and then out to the duovalve. - current = open no current=closed.This is a blind guess though. :?

Anyone know how it actually works?

 

[w201]

On the 190 it?s a vacuum operated valve [not a duovalve] that operates the temp. When the 2 heater compartment adjustments are set to cold I tried disconnecting the valve and connecting a piece of copper pipe where the valve is to no avail the same problem occurs I am starting to think that it may be a flap inside the heater itself that is not operating properly.

 

[LNM]

shiiiiit, if I disconnect the fan that draws air from the cabin through the little grille on the roof console (which I have done because it was noisy) this implies that the heating adjustments will go all to buggery.

I've just answered my own question havent I ?

Shutting up right away.

£40 from a dealer I believe for a new fan?

 

[LNM]

shiiiiit, if I disconnect the fan that draws air from the cabin through the little grille on the roof console (which I have done because it was noisy) this implies that the heating adjustments will go all to buggery.

I've just answered my own question havent I ?

Shutting up right away.

£40 from a dealer I believe for a new fan?

 

[jberks]

wont help.