| Description and Operation The heater temperature is set using the temperature control switch. Depending on the setting of this switch, the heater control module (located in the heater/air conditioning system controls), monitors the position of the heater control valve, which in turn controls the flow of hot coolant through the heat exchanger. The position of the air distribution flap is adjusted by a splined shaft. The recirculated air flap is operated by a control motor. The blower motor has four speeds, controlled by the blower motor operating switch through a resistance. If the air conditioning system is switched on but the blower motor switch is off, the air conditioning system will not operate. The air conditioning system will only operate if the blower motor is on. Procedure if there are regular knocking noises coming from the fascia crash padding area. The water flow through the heater control valve can cause a regular knocking noise when the operating temperature switch is set between Min and Max. This noise is carried into the interior of the vehicle via the fascia/crash padding and can be intensified if any air is trapped in the system. If concerns are expressed over this, the noise can be reduced by installing modified insulation on the heater control valve along with a modified heater coolant hose.
For additional information, refer to Heater Control Valve in this section.
Modified components have been installed in production since 16.08.99 in Dagenham and since 09.08.99 in Cologne. Procedure if the heating cannot be controlled. If there is a concern that the heating cannot be controlled (only hot air or only cold air is produced), the cause may be a damaged wiring harness, damaged multiplug, a defective heater control valve or a defective heater control. To resolve the concern, check the heating system and renew any damaged components. An additional cover should be installed on the heater control valve on the vehicle. For additional information, refer to Section 412-00 Climate Control System - General Information.Diagnosis and Testing A cover has been installed on the heater control valve on vehicles in production since 02.97 (build code VU). | 
