A/C Compressor Regulator Valve N280, Checking Activation Signal
Special tools and workshop equipment required
- Connector Test KitV.A.G 1594 C
- Diagnostic Operation SystemVAS 5051 A
- DSO measuring leads 1 & 2VAS 5051/8
-- Switch off ignition.
-- Remove noise insulation. Refer to NOISE INSULATION, REMOVING AND INSTALLING .
-- Unplug connector at air-conditioner compressor.
-- Reproduce the connection between connector -A- and connector -B- at regulator valve using an adapter cable from V.A.G 1594 C.
This illustration shows the connector -B- on an A/C compressor on a 6 cylinder engine. For the correct allocation for vehicles with a different engine, refer to COMPRESSOR .
The A/C compressor regulator valve activation and the current flowing through the A/C compressor regulator valve measured by the Climatronic control module -J255- is displayed in the Climatronic control module measured values block using Vehicle Diagnosis, Testing and Information System VAS 5051 in the "Guided Fault Finding" function.
Certain functions on the A/C compressor regulator valve -N280- (for example, a stuck valve or a disruption in the coil) can lead to a complaint regarding the A/C compressor (A/C system doesn't cool, the evaporator ices over, etc.). If the cause is with the A/C compressor regulator valve -N280- (and not the A/C compressor itself), the A/C compressor can be serviced by replacing the valve -N280-. Refer to A/C Compressor Regulator Valve -N280- (Refrigerant R134a, Servicing; Refrigerant Circuit Components, Replacing).
The A/C compressor regulator valve -N280- is not available as a replacement part for all A/C compressors. If the A/C compressor regulator valve -N280- is not available as an individual A/C compressor part (different versions), then the entire A/C compressor must be replaced.
If connectors to A/C compressor regulator valve and to electric engine mount are interchanged, no DTC is entered in DTC memory (the electrical values of these components are about the same), however the evaporator may ice-up since the compressor is actuated continuously.
An adapter cable can also be used for this test. To do this, for example, use one connector each -A- and -B- (part number 1J0 973 702 and 1J0 973 802 and relevant terminal contacts), two standard sockets for banana connectors -C- and two wires with 0.5 mm 2 diameter.
-- Connect DSO measuring leads 1 & 2VAS 5051/8 to adapter leads.
-- Measuring lead (signal wire) to wire to connector terminal -2-.
-- Measuring lead (shielding, Ground) to wire to connector terminal -1-.
-- Set operating mode Test Instruments DSO (Digital Storage Oscilloscope) on VAS 5051 A.
-- Setting 5V/Div = 0.5 ms/Div (5 volts DC and 0.5 milliseconds per unit)
-- Start engine.
-- Set temperature preselect on Climatronic Control Module to Cold (for example, temperature preselect Lo for driver's and front passenger's side).
-- Turn the A/C compressor regulator valve on and off on the Climatronic control module by pressing the Econ button or the AC or A/C button.
Shown on screen of oscilloscope, depending on setting of Climatronic control module:
-- No square wave signal (A/C compressor regulator valve is not activated) for operating mode OFF and Econ or A/C off.
-- A square wave signal with an impulse width -A- between 75% and 100% (regulator valve is activated) for operating mode Auto (or with compressor switched on) and temperature setting Lo.
The Fig. shows a signal with a duty cycle of approximately 80%.
Impulse width -A- is dependent on desired cooling performance, vehicle voltage etc. (over the width of region -A-, voltage is regulated via A/C compressor regulator valve by Climatronic Control Module).
The signal distance -B- is always 2 milliseconds (corresponds to frequency of 500 Hertz).
The duty cycle is determined by the ratio of impulse width -A- and signal distance -B-.
-- The impulse width of the square wave signal changes (duty cycle between 100% and greater than 30%, regulator valve is activated so that required compressor output is obtained to reach the specified temperatures) depending on setting at Climatronic Control Module and measured surrounding conditions.
At setting of maximum cooling performance (for example, operating mode Auto and temperature setting Lo on Comfort version), A/C compressor regulator valve is activated so that the maximum permissible current of approximately 0.65 A flows via A/C compressor regulator valve (maximum compressor output).
In control mode, actuation time is governed by required cooling output and vehicle electrical system voltage, for example. It is however always of sufficient duration to achieve a mean current of 0.3 A.