Operation and actuation of heater coolant shutoff valve N279 — AUDI

Operation and actuation of
heater coolant shutoff valve
N279
Note
In the case of auxiliary heaters with part number 4F0 265 081 up to index
“L”
(up to software version
“060”
), an
“open circuit / short to positive”
may be erroneously detected as a sporadic fault at the
coolant shut-off valve
N279
under certain usage conditions. This entry in the fault memory need only be heeded in the event of problems with the auxiliary heater. If there are no problems with the auxiliary heater, erase the erroneous fault memory entry if applicable (do not perform any further fault-finding).
Operation of
heater coolant shutoff valve
N279
In auxiliary heating mode,
heater coolant shutoff valve
N279
is actuated by
auxiliary heater control unit
J364
, depending upon operating status of auxiliary heater, setting in MMI (Multi Media Interface) and upon coolant temperature in engine and in auxiliary heater
Anchor
.
If voltage is not applied to
heater coolant shutoff valve
N279
, coolant flows from connection
3
(from air conditioner heat exchanger) to connection
4
(to engine, large coolant circuit).
If voltage is applied to connection
A
(e.g. in auxiliary heating mode with cold coolant and engine stopped), coolant flows from connection
3
(from air conditioner heat exchanger) to connection
1
to auxiliary heater (small coolant circuit).
Note
Connection
2
is sealed.
Actuation of
heater coolant shutoff valve
N279
Note
Actuation of
heater coolant shutoff valve
N279
is dependent upon coolant temperature on activation and upon operating status of vehicle (e.g.
“Engine running”
).
If auxiliary heater is operated as additional heater
auxiliary heater control unit
J364
compares coolant temperature of auxiliary heater and engine and only actuates
heater coolant shutoff valve
N279
if coolant temperature of auxiliary heater is greater than that of engine.
The display in the measured value block for actuation of the
heater coolant shut-off valve
N279
differs and depends on the vehicle model and the version of the
supplementary heater control unit
J364
. On the Audi A6 at present for example, a display of 100 % indicates that 100 % of the coolant is being conveyed in the small circuit and that the
heater coolant shut-off valve
N279
is being actuated
Vehicle diagnostic, testing and information system
VAS 5051 A
, "Guided fault-finding" function.
If
heater coolant shutoff valve
N279
is not actuated, 100 % of coolant flows in large circuit.
A
This proportion of coolant in % is conveyed in large coolant circuit.
Heater coolant shutoff valve
N279
is actuated by
auxiliary heater control unit
J364
in accordance with coolant temperature and request set.
B
Temperature of coolant in auxiliary heater in °C
C
Activation signal for auxiliary heater (also as additional heater) via convenience data bus system
D
Start of full-load operation following start of auxiliary heater. In full-load operation,
heater coolant shutoff valve
N279
is actuated via various curves depending upon coolant temperature
E
Switching to part-load operation of auxiliary heater
F
Part-load operation of auxiliary heater
G
Switching from part-load operation to control interval
H
Auxiliary heater is in control interval, coolant temperature continues to increase, e.g. with engine running
J
Auxiliary heater is in control interval, coolant temperature decreases (also with engine running, if more heat is dissipated by air conditioner heat exchanger than engine generates)
K
New start of auxiliary heater out of control interval
Note
Depending on ambient temperature and amount of heat dissipated by air conditioner heat exchanger,
heater coolant shutoff valve
N279
actuation may remain in the various operating statuses for a lengthy period.
Actuation of
heater coolant shutoff valve
N279
is also maintained even if engine is started with auxiliary heater running.
At a coolant temperature of approx. 91 °C, auxiliary heater switches from control mode to control interval. If
heater coolant shutoff valve
N279
is not actuated during control interval, coolant flows in large circuit.