2007 Tucson heater blowing cold air
 

Our 2007 Tucson Limited (2 litre diesel, RHD UK model) only blows cold air from the heater.
The engine warms up normally, so thermostat is working, coolant level is correct. The pipes into, and out of, the heater matrix both get hot, so I don't think that is clogged. Changing through the various modes blows a strong blast of (cold) air through the correct vents. Is there a flap on the heater matrix that opens and closes to let the hot air into the cabin?
If there is, how do I get to it, and how does it work? Is it sensor operated? Would it show a fault code if I got someone to plug it in to a code reader?
This happened suddenly, it wasn't a gradual thing, if that helps at all.


Many thanks


Barry

One hose to heater core should be hot
The other one should be lots cooler
Seems like the heater core is full of deposits blocking the transfer of heat into the cabin.

Thanks for the reply, are you sure the return pipe should be cooler? I thought the heater matrix circulated hot water from the engine for the heater to use if required? If it was clogged up then the water in the return pipe would be cold wouldn't it? If the water coming out is hot then it must be flowing freely?
That's certainly the way it works on my 50 year old classic car, where everything is easy to get to and there are no sensors or electrics involved. If you want warm air, a fan blows air through the heater matrix, if you want cold air, you open the window or put the roof down.

If the heater core is clogged then the return hose would be cold
There would be no flow so no heat out
But, if the heater core just has deposits blocking the transfer of heat
then the return hose would stay hot
There would be no transfer of heat to the cabin air
A good working heater core will take hot coolant in and return cooler coolant out
The heat would transfer to the cabin air and the return hose would be cooler
To most people, it would probably just feel hot but it is cooler

Try reverse flushing the heater core
And there are no sensors in the heater core for the ECU to put up a Diagnostic Trouble Code