hi
if your saying the heater only blows hot, even if set to cold, its a common problem on s-types
its either the DCCV in the engine bay, dual coolant control valve or climate module or both
when the dccv fails it sticks either open or shut, but if they get water in the plug, which usually corrodes due to water, it blows the pcb tracks in the climate module
the module can be easy repair, when removed and opened you will see blown copper tracks, they need soldering
also if you buy a new dccv, cheap ones dont last long at all, better off with a bosch one
cheers
Joe