Checking cut-in signal for air conditioner compressor regulating valve N280 — AUDI

Checking cut-in signal for
air conditioner compressor regulating valve
N280
Note
The following describes the procedure for checking a
“Denso”
air conditioner compressor (type
“6 SEU 14”
) without
air conditioning system magnetic clutch
N25
. Perform the check in the same manner on vehicles with a different type of compressor or a compressor from a different manufacturer.
The difference on air conditioner compressors with
N25
is that a 3-pin connector may be installed
Current flow diagrams, Electrical fault finding and Fitting locations
.
In the following the checking procedure is described for vehicles with a 6-cyl. TDI engine; the procedure may differ for vehicles with a different engine (4-cyl., 6-cyl. or 8-cyl. engine).
Not fitted on vehicles with an electrically driven air conditioner compressor.
Certain malfunctions of
N280
(e.g. sticking valve or open circuit in coil) can lead to problems with the air conditioner compressor (no cooling output from air conditioner, evaporator icing up etc.). If
N280
(and not the air conditioner compressor itself) is the cause of the problem, the air conditioner compressor can be serviced by renewing
N280
Air conditioner with refrigerant R134a
Rep. gr.
87
Renewing components of refrigerant circuit
.
N280
is not available as a replacement part for all air conditioner compressors. If
N280
cannot be obtained separately for a particular air conditioner compressor (different versions available), the entire air conditioner compressor must be renewed if problems occur
Electronic parts catalogue
.
On air conditioner compressors with
N25
, you may have to discard plug contacts from connector housing on
N280
before renewing
N280
Air conditioner with refrigerant R134a
Rep. gr.
87
Renewing components of refrigerant circuit
.
Preparation
Switch off ignition.
Remove noise insulation (front)
General body repairs, exterior
Rep. gr.
66
Noise insulation; Exploded view - noise insulation
.
Test sequence
Unplug electrical connector
B
at
air conditioner compressor regulating valve
N280
A
.
Use an adapter cable to re-connect connector
A
and connector
B
at
air conditioner compressor regulating valve
N280
.
Note
Different adapter cables must be used, depending on the version of the air conditioner compressor (with or without
air conditioning system magnetic clutch
N25
). For example,
test instrument adapter/DSO (3-pin)
VAS 5257
must be used for an air conditioner compressor without
N25
, and
test instrument adapter/DSO (2-pin)
VAS 5256
must be used for an air conditioner compressor with
N25
. If no suitable adapter is available, you can establish the connection between connector
A
and connector
B
with components from the
auxiliary measuring set
V.A.G 1594 C
.
Alternatively, you can use an improvised adapter cable for this test. For this you will need e.g. one 2-pin connector each (
A
and
B
; part numbers 1J0 973 702 and 1J0 973 802 and the corresponding plug contacts), two commercially available sockets for banana plugs
C
and two cables (cross-section = 0.5 mm
2
) for an air conditioner compressor without
N25
.
The
air conditioner compressor regulating valve
N280
is activated by the
onboard supply control unit
J519
when requested by the air conditioner operating and display unit (
Climatronic control unit
J255
)
Vehicle diagnostic, testing and information system VAS 5051 ("Guided Fault Finding")
and
Current flow diagrams, Electrical fault finding and Fitting locations
.
The top illustration shows an air conditioner compressor without
N25
on which the 2-pin connector
A
to the vehicle wiring harness is plugged in directly at the
air conditioner compressor regulating valve
N280
(connector
B
). Depending on the version of the air conditioner compressor, the connector
B
may also be provided with a short wire.
The activation of the
air conditioner compressor regulating valve
N280
is displayed in the measured value block of the
onboard supply control unit
J519
. The maximum control current depends on the version of the operating and display unit (
Climatronic control unit
J255
)
Vehicle diagnostic, testing and information system VAS 5051 ("Guided Fault Finding")
and
Current flow diagrams, Electrical fault finding and Fitting locations
.
The measured current flowing via the
air conditioner compressor regulating valve
N280
is displayed in the measured value blocks of the air conditioner operating and display unit (
Climatronic control unit
J255
) and the
onboard supply control unit
J519
Vehicle diagnostic, testing and information system VAS 5051 ("Guided Fault Finding")
.
If the required actual current does not flow via the
air conditioner compressor regulating valve
N280
, check the positive and earth connections of the
onboard supply control unit
J519
and the wiring between
J519
and
N280
on the basis of the current flow diagram for open circuit, contact resistance and interchange
Current flow diagrams, Electrical fault finding and Fitting locations
.
Connect
probe
VAS 5051/8
to adapter cables.
Test lead (signal wire) to contact
2
of connector
B
Test lead (screen, earth) to contact
1
of connector
B
Note
On an air conditioner compressor with a different connector (e.g. a 3-pin connector on an air conditioner compressor with
N25
), pay attention to the pin assignment when connecting the test cables
Current flow diagrams, Electrical fault finding and Fitting locations
.
On
vehicle diagnostic, testing and information system
VAS 5051/
, set testing mode DSO (Digital Storage Oscilloscope).
Then select 5 V/div = 0.5 ms/div (5 V DC and 0.5 milliseconds per unit).
Start engine.
Set temperature on air conditioner operating and display unit (
Climatronic control unit
J255
) to maximum cooling output.
Press
AC
or
A/C
button (with lamp indicating when air conditioner compressor is switched on) on air conditioner operating and display unit (
Climatronic control unit
J255
) to activate and deactivate
air conditioner compressor regulating valve
N280
.
Depending on the setting of the air conditioner operating and display unit (
Climatronic control unit
J255
), the display of the oscilloscope will show:
In
“OFF”
or
“AC off”
mode (indicator lamp in
“AC”
or
A/C
button off), there is no square-wave signal (
air conditioner compressor regulating valve
N280
is not activated).
In
“Auto”
or
“AC on”
mode (indicator lamps in buttons on) and with the temperature set to maximum cooling output, there is a square-wave signal with a pulse width
A
of between 75 % and 100 % (regulating valve is activated).
Note
The illustration shows a signal with a duty cycle of approx. 80 %.
The pulse width
A
is governed by the required cooling output and the electrical system voltage etc.; over the width of area
A
the current is controlled via the
air conditioner compressor regulating valve
N280
by the
onboard supply control unit
J519
on the basis of the request from the air conditioner operating and display unit (
Climatronic control unit
J255
).
The signal distance
B
is always 2 milliseconds (corresponding to a frequency of 500 Hertz).
The duty cycle is derived from the ratio of pulse width
A
to signal distance
B
.
The setting on the air conditioner operating and display unit (
Climatronic control unit
J255
) and the measured ambient influences govern the pulse width of the square-wave signal (duty cycle between 30 % and 100 %, the
air conditioner compressor regulating valve
N280
is actuated so that the compressor output required to obtain the specified temperatures is achieved).
Note
In
“Auto”
and
“AC on”
mode (indicator lamps in buttons on) and with the temperature set to
“Lo”
, the
air conditioner compressor regulating valve
N280
is activated so that the maximum permissible current of approx. 0.65 A flows via the
N280
(maximum compressor output).
In control mode, the activation time is governed by the required cooling output and the voltage of the vehicle's electrical system, for example; however, it is always long enough to achieve a mean current of 0.3 A.