'88 300D heating problem "only hot air"

Hi
Ive just bought an old 300D and there is a problem with the heating system.. when the car is varm, only HOT air is coming out of the fans. A friend told
me to change the heatpump, but that didnt solve the problem Can anyone help me on what the problem can be? its really a problem, course its really getting pretty hot inside the cabin hehe thu i live in cold denmark, thats still a little too much
thx in advance Michael
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The heater control valve, called the "mono valve" needs to be repaired. It can be rebuilt with a kit. The cabin gets full heat (default mode) when the mono valve fails.
The mono valve is located between the car's engine and the firewall (below the windshield).
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My '87 300td does not have a "monovalve" and it's possible that the OPs 300D also lacks one. There is a similar valve, contolled by the Climate Control circuit, but it is not structured the same as a monovalve and is not rebuildable.
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im not sure, but i changed a device near the battery, I call it a "hot air pump" but im not sure thats the right name, maybe its mono valve, but it didnt solve the problem ???

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the mono valve will also blow hot air if it looses its live feed surely its better to check for live feed to plug and check fuses before replacing valve
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hmm to start with, it only blow really hot air out occaitionally, sometimes first when i have been driving for 2 hours. i could often "fix" the problem by setting the fan speed to max for 30 sek. then cold air came back. Now i cant "fix" it anymore, as soon the engine is varm, it blows hot air out. So that can not be the live feed then right? as I wrote a few post ago, I got my friend to change a thing I call a "hot pump" and still the same problem.. I was trying to find a picture of that thing we replaced, but cant really find one..
http://69.0.158.19/live/R302211892OES.JPG this one came closest, but its still not the one. The one we replaced got 2 metallic chambers.

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finally i found a picture of the device we replaced
http://www.germanstar.net/Pics/0008307284.jpg
and still i have the hot air problem. I will check the fuse and live feed tomorrow, but sence the problem at first, only showed up accasionally, it might not be that. Can anyone think of something else that could be the problem??
Thx for the help btw :-) and merry christmas

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The device in the picture looks to me to be the auxiliary water pump. It runs only within a certain temperature range inside the heater to boost water flow to the heater core. This is NOT THE PROBLEM.
You need to check (and probably replace) the heater control valve that must be located very close to the auxiliary water pump.
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This is the water flow valve. I have exactly the same on my '87 300TD. I have had it apart, so I know it's not the auxiliary water pump. Actually, there is no auxiliary water pump.
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The first picture you mentioned ("
http://69.0.158.19/live/R302211892OES.JPG ") is the mono valve. But the picture mentioned below is the water pump, which cannot be the problem. So which one did you actually replace?
If it looks like the mono valve but kind of double it, that is still the mono valve. Some cars have separate driver/passenger control. The first picture shows the single control.
mengo wrote:

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the device I replaced is this one
http://www.germanstar.net/Pics/0008307284.jpg its hard to see on the picture, but mine had double thingies
Im a bit confused now... what do i need to replaced if its not the one i allready replaced

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If you wanna reach me on msn instaed, use my email adress. As you probely allready know im not either english or a car expert :-)

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Check the connection at the valve controlling waterflow to the heater, it's near the battery. If it is not a monovalve (and maybe if it is), the valve will be normally open when the engine is running. An electric current closes it.
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