hi
have a look at the dccv, Dual coolant control valve
its a water valve that control hot water to the l/h and r/h heater matrix
there 2 solenoids, when heat is on, there will be 12volts there, water will flow and you will get hot pipes
if you put it on lowest temp, then the solenoid should close, no volts on the solenoids, if the pipes both still get hot, the valve are stuck open and your aircon will never blow cold
cheers
Joe