"At low engine speed the electric auxiliary coolant pump directs coolant flow through the monovalve/heatercore/bypass flow circuit"
This is the coolant recirculating pump that is used by the ACC to ensure that enough heated coolant is continuously circulating through the heatercore. Apparently the engineers discovered that at idle speed less heated coolant was flowing through the heater core, then as soon as the engine RPMs increased much more flow occurred, this rapidly changing heater core flow condition caused the ACC control to overreact in some way or not react quick enough. The solution was to install the electric auxiliary coolant pump that is controlled ye the ACC unit turning the pump on when insufficient coolant was flowing thereby moderating the flow fluctuations and allowing the ACC to operate with the desired heat flow into the cabin.
A cheap, easy, and valuable DIY project is to install an inline fuse for this pump. The pump failing it the "lock-up" mode will cause excessive current flow through the controlling circuitry and the PC board traces in the ACC pushbutton unit, at $200 for a rebuilt unit, $5 and 30 minutes is cheap insurance! Obviously your car's pump failed once already and you appear to have luckily avoided the failed controller syndrome!! Check here!
140 Phones from MBNA