AIR CONDITIONING (page 3 of 7)

AIR CONDITIONING

DESCRIPTION AND OPERATION

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Heater Coolant Circuit - With FBH

1 Coolant valve (low line system)
2 Heater matrix
3 Coolant valves (high line system)
4 Auxiliary coolant pump

5 Engine cooling system
6 ATC ECU
7 Changeover valve
8 FBH unit

Additional Heating
On Td6 models, additional heating reduces the heater warm-up time and is also used to maintain heater performance 
throughout the drive cycle. On V8 models, additional heating is only used to reduce the heater warm-up time at the 
beginning of the drive cycle, and only occurs if parked heating is already active when the engine starts.

The ATC ECU activates the additional heating mode when the engine is running and the following conditions coexist:

l

The ambient temperature is less than 8 

°

C (41 

°

F)

l

The engine coolant temperature is less than 75 

°

C (167 

°

F)

l

The heater coolant temperature is less than 70 

°

C (158 

°

F)

l

The reference temperature is 100%

l

The blower is on.

To activate the additional heating mode, the ATC ECU energises the auxiliary coolant pump and sends K bus 
messages to the FBH unit to start/continue operation (the changeover valve remains de-energised).

M82 0820

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