Symptom Related Diagnostic Procedures

Parking Heater Information if Heat Output is Poor

If a customer complains of poor heating performance, check heat output of A/C system. Refer to=> [ Heating Performance Of A/C System, Checking ] Heating Performance Of A/C System, Checking.

In vehicles with a parking heater installed as optional equipment, if there is a complaint of poor or insufficient heating performance at low engine speeds, check activation of Engine Coolant (EC) Switch-Off Valve (heater) (N279) and of Recirculation Pump (V55) of parking heater by Auxiliary Heater Control Module (J364).

• Engine Coolant (EC) Switch-Off Valve (heater) (N279) is activated when parking heater is switched off and ignition is switched on. If shut-off valve is activated, coolant does not flow directly from heater core to engine (rather via the parking heater). With parking heater switched on, Engine Coolant (EC) Switch-Off Valve (heater) (N279) is only then actuated with ignition switched on e.g. when coolant temperature in parking heater is greater than the coolant temperature in the engine.

• By activating Recirculation Pump (V55) , coolant flow through A/C system heater core is increased at lower engine speeds and thus better heating performance is achieved.

• The auxiliary heater control module switches on the recirculation rump when the following information is received via the Data bus:

- Ignition on and engine running.

- Outside air temperature lower than 20 °C.

- Engine speed less than 2,000 rpm.

- Vehicles with automatically regulated A/C system: Climatronic Control Module (J255) is switched on and "heating output" is requested for at least one side (driver or front passenger side).

- Using the A/C ( A/C control module (J301) ) requires heating, the temperature rotary switch is turned to "warm" (on vehicles with a manual climate control system). Check using Vehicle diagnosis, testing and information system (VAS5051B) in "Guided Fault Finding" function.

• Recirculation pump is switched on as soon as all the requirements are met. To stop circulation pump being constantly switched off and on, it remains activated for at least 30 seconds even if - for example in the event of rapid changes in vehicle speed - a request is only applied for several seconds (e.g. on accelerating after standing at traffic lights).