Heater Control Valve: Description and Operation

Water Valve Assembly

Heater System Components - XK Series:

The water valve assembly is located above the water pump, in the engine compartment and is secured to the firewall by a bracket. The valve operates by means of an electrical solenoid which oscillates the valve stem between the inlet and outlet ports.

A heat shield protects the water valve from exhaust system radiated heat.

When in automatic mode, the water valve is controlled by the following inputs to the A/CCM:
Face outlet temperature, corrected for solar loading
Air off heater matrix temperature
External ambient display temperature
Coolant temperature
Engine speed (valve closed with the engine not running)
Demand (set) temperature

Re-heating of the refrigerated air is controlled by the time that the water valve is open (i.e. not energized) over a six second interval. The duty cycle of the water valve, the time open / time closed, is controlled by the A/CCM.

Maximum heating demand will cause the water valve to be fully open (not energized) to allow maximum coolant flow through the heater matrix.

At Maximum cooling, the water valve will be fully closed (energized) to prevent hot (engine temperature) coolant entering the heater circuit; the pump however will continue to circulate coolant through both the heater matrix and water valve bypass.

The water valve defaults open when the ignition is OFF.

Under engine stall conditions, when ignition is ON, the water valve will be open.