Soggy Cardboard??
There is no carboard type of material anywhere in the system. The closet things to it would be the pollen filter and the air filter.
Are you sure someone has not put a lump of cardboard in the slot between the rads to make the heaters work better by blanking off the incoming air? It used to be a very old dodge but was fraught with danger of overheating when the weather got warmer.
Had my condenser changed and the whole system re-gassed properly for £234.00 inclusing the new drier.
All bits are fixed by a couple of bolts, pipe unions and banjo bolts, nothing is welded. Make sure both plastic location pegs go into the bottom grommets too.
If your system is totally empty you can change the Condenser yourself with ease, remember to use new seals and a new drier though! There is a guide in the Maintenance Section of the forum. Don't drive it too far before you get it re-gassed either.
GudLuk