MERCEDES ML 270cdi W163 2002 Auto - SECONDARY COOLANT PUMP ?

[13enzy]

Hi
Does anyone know what exactly does the secondary coolant pump do and why is it important ?

 

[W221copea]

Im no expert on this, but do you have rear aircon as an option on the car? I have two of these one for front and one for rear, different units.....

 

[whitenemesis]

Do you have the Rest function in the car? This function, part of the climate control system, allows residual engine coolant heat to be used whilst parked up, engine off. Obviously there needs to be a separate pump to circulate the coolant.