Operation of heater coolant shut-off valve — AUDI

Operation of heater coolant shut-off valve
Note
The fitting location, designation and version of the heater coolant shut-off valve
N279 depend on the version and equipment of the vehicle. It is therefore important to observe the correct assignment
Electronic parts catalogue.
The heater coolant shut-off valve
N279 is actuated by the auxiliary heater control unit
J364 in line with the coolant temperature and the request set (repair group 82: Coolant circuit with auxiliary/supplementary heater) and
Vehicle diagnostic tester
“Guided fault-finding” mode.
If voltage is applied to the heater coolant shut-off valve
N279 (small coolant circuit), the coolant flows from the connection (3) (from the heat exchanger in the front and, if fitted, the rear heater and air conditioning unit) to the connection (1) (to the circulation pump
V55).
If voltage is not applied to
N279 (large coolant circuit), the coolant flows from the connection (3) (from the heat exchanger in the heater and air conditioning unit) to the connection (2) (to the engine).
There are different versions of
N279 (with 3 or 4 connections for coolant hoses). On the version with 4 connections, one connection is sealed with a cap.
Depending on the installation position of
N279
, the cap shown may also be fitted at the connection (1).
In auxiliary/supplementary heating mode,
N279 is actuated by the auxiliary heater control unit
J364 until the coolant temperature in the auxiliary/supplementary heater has reached a specified level
Vehicle diagnostic tester
“Guided fault-finding” mode.
Depending on the vehicle model, the engine fitted, the coolant temperature and the setting on the front air conditioner operating and display unit
E87
, actuation may also be implemented by the auxiliary heater control unit
J364 with the auxiliary/supplementary heater switched off. Actuation then takes place in response to a request from
E87 via the data bus.
In the event of problems with poor heating of the passenger compartment in auxiliary/supplementary heating mode and also with the engine running, check the incorporation of
N279 into the coolant circuit and actuation of
N279 by the auxiliary heater control unit
J364 (see the separate procedure) and
Vehicle diagnostic tester
“Guided fault-finding” mode.
The connection numbers printed on
N279 depend on the version and may differ from the numbering shown in this illustration.
In auxiliary/supplementary heating mode,
N279 is constantly actuated by the auxiliary heater control unit
J364 up to a coolant temperature of approx. 81°C (degrees centigrade) in the heater (actuation 100%). As long as
N279 is being actuated, the coolant flows in the small circuit (from the auxiliary/supplementary heater via
N279 and the heat exchangers in the heater and air conditioning units back to the auxiliary/supplementary heater) .
At coolant temperatures between approx. 82°C and approx. 88°C in the heater,
N279 is actuated by
J364 by way of a characteristic curve. Depending on actuation, the coolant flows in the small circuit or in the large circuit (from the auxiliary/supplementary heater via
N279
, the heat exchangers in the heater and air conditioning units and the engine back to the auxiliary/supplementary heater).
As of a coolant temperature of approx. 88°C in the heater,
N279 is no longer actuated by
J364
. The coolant flows in the large circuit.
In auxiliary/supplementary heating mode, the coolant is conveyed by way of the circulation pump
V55 in the large or small circuit.
V55 is actuated by the auxiliary heater control unit
J364 (repair group 82: Coolant circuit with auxiliary/supplementary heater).
Note
Depending on the ambient temperature and the quantity of heat emitted by the heater and air conditioner heat exchangers, the actuation of the heater coolant shut-off valve
N279 may remain in the various operating statuses for a lengthy period.
Actuation of the heater coolant shut-off valve
N279 is also maintained if the engine is started with the auxiliary/supplementary heater in operation and the coolant in the engine is colder than the coolant in the auxiliary/supplementary heater.
There are different versions of the heater coolant shut-off valve
N279
. Pay attention to correct assignment
Electronic parts catalogue.
At a coolant temperature of approx. 91°C, the auxiliary/supplementary heater switches from control mode to control interval. During the control interval, the heater coolant shut-off valve
N279 is not actuated and the coolant flows in the large coolant circuit (via the engine).
The display in the
“Reading measured values” function for actuation of the heater coolant shut-off valve
N279 differs and depends on the vehicle model and the version of the auxiliary heater control unit
J364
. On this vehicle, a display of 100% for example currently indicates that all the coolant is being conveyed in the small circuit and that the heater coolant shut-off valve
N279 is being actuated
Vehicle diagnostic tester
“Guided fault-finding” mode.
Depending on the vehicle model, the engine fitted, the coolant temperature and the setting on
E87
, the heater coolant shut-off valve
N279 may also be actuated by the auxiliary heater control unit
J364 with the auxiliary/supplementary heater switched off. Actuation then takes place in response to a request from
E87 or from the corresponding engine control unit
J623 via the data bus
Vehicle diagnostic tester
“Guided fault-finding” mode (reading measured values).
Depending on the vehicle model, the engine fitted, the coolant temperature and the setting on
E87
, the circulation pump
V55 may also be actuated by the auxiliary heater control unit
J364 with the auxiliary/supplementary heater switched off. Actuation then takes place in response to a request from
E87 or from the corresponding engine control unit
J623 via the data bus
Vehicle diagnostic tester
“Guided fault-finding” mode (reading measured values).