Activation of heater coolant shut-off valve N279 — AUDI

Activation of
heater coolant shut-off valve
N279
The operating unit of the
Climatronic control unit
J255
calculates the heating period of the auxiliary heater such that the specified passenger compartment temperature is attained at the selected time. This means that the auxiliary heater generally remains in full load mode and the coolant temperature remains below the threshold for switching to the large circuit.
There is currently no provision for pre-heating the engine.
This illustration shows one possible example of
heater coolant shut-off valve
N279
activation. As the auxiliary heater control system on this vehicle already switches to part load at a coolant temperature of approx. 77°C, it rarely switches to the large circuit.
A = This proportion of the coolant in % is conveyed in the large coolant circuit.
If the
heater coolant shut-off valve
N279
is not activated, 100 % of the coolant is delivered in the large circuit (via the engine to the auxiliary heater).
If the
heater coolant shut-off valve
N279
is constantly activated, 100 % of the coolant is delivered in the small circuit (directly from the heat exchanger in the air conditioning unit to the auxiliary heater).
The
heater coolant shut-off valve
N279
is activated by the
auxiliary heater control unit
J364
in line with the coolant temperature and the specified request.
B = Temperature of coolant in auxiliary heater in °C (degrees Celsius).
C = Activation signal for auxiliary heater (the
heater coolant shut-off valve
N279
is activated and the coolant flows back from the heat exchanger in the air conditioning unit to the auxiliary heater).
D = The auxiliary heater is in auxiliary heating full load mode; the coolant temperature increases (or remains constant). All the coolant drawn in by the
circulation pump
V55
comes from the air conditioner heat exchanger.
E = The auxiliary heater is in auxiliary heating full or part load mode. Depends on the characteristic curve stored in the
auxiliary heater control unit
J364
. The coolant temperature increases (or remains constant) and the proportion of the coolant (drawn in by the
circulation pump
V55
) which flows back via the engine to the auxiliary heater is regulated by the
auxiliary heater control unit
J364
. This operating status is encountered rarely or not at all on this vehicle due to the auxiliary heater control system.
F = All the coolant drawn in by the
circulation pump
V55
flows back via the engine to the auxiliary heater; the coolant temperature continues to increase (less heat is emitted by the air conditioner heat exchangers than is generated by the auxiliary heater or e.g. with the engine running - refer to -E-).
G = All the coolant drawn in by the
circulation pump
V55
flows back via the engine to the auxiliary heater; the coolant temperature decreases (more heat is emitted by the front air conditioner heat exchangers or the engine than is generated by the auxiliary heater and the engine - refer to -E-).
H = The coolant temperature drops below 65 °C.
Note
Depending on the ambient temperature and the quantity of heat emitted by the air conditioner heat exchangers, the activation of the
heater coolant shut-off valve
N279
may remain in the various operating statuses for a lengthy period.
Activation of the
heater coolant shut-off valve
N279
is also maintained if the engine is started with the auxiliary heater in operation.
Different auxiliary heater versions; this vehicle is currently fitted with an auxiliary heater on which the
heater coolant shut-off valve
N279
is almost always activated in auxiliary heating mode (when the engine is not running).
There are different versions of the
heater coolant shut-off valve
N279
. Ensure correct assignment
Electronic parts catalogue
.
At a coolant temperature of approx. 89 ℃, the auxiliary heater switches from control mode to control interval. During the control interval, the
heater coolant shut-off valve
N279
is not activated and the coolant flows in the large coolant circuit (via the engine).
The display in the
“Read measured values”
function for activation of the
heater coolant shut-off valve
N279
differs and depends on the vehicle version and the version of the
auxiliary heater control unit
J364
. On this vehicle for example, currently a display of 100 % indicates that 100 % of the coolant is being delivered in the small circuit and that the
heater coolant shut-off valve
N279
is being activated
Vehicle diagnostic tester
(
“Guided Fault Finding”
).
Depending on the vehicle version, the engine installed, the coolant temperature and the setting on the air conditioner operating unit (
Climatronic control unit
J255
), the
heater coolant shut-off valve
N279
may also be activated by the
auxiliary heater control unit
J364
with the auxiliary heater switched off. In this case, the activation is a response to a request from
J255
via the data bus
Vehicle diagnostic tester
(
“Guided Fault Finding”
).