Terios '99 - locating the heater matrix


Hello everybody,

I've some issues with my Terios J1..
First of all the previous owner of the car has been pouring coolant leak repair liquid /there was a leak from the engine block but we changed the block and everything is fine/.
Now I think that the heater core is clogget because the heater blows cold. I checked all the vents for the cold/warm but there isn't a problem. I'm determined to replace the heater core. I took a quick look inside and saw a big box /it's not really a box but .. I don't know what is it and for what is it/. I dismounted the glove compartment and saw this "box" - there is the recirculation valve on it and the heater pipes are inside the "box". I can't explain it very well, sorry.
It was late and I could not open this box to see what's inside. I think the heater core should be there but some of my friends told me that it will be behind the heater control panel.

Could someone tell me where it is located Unknw Or are there drawings of the heating system Unknw