Compressor HVAC: Testing and Inspection

Cut-in Signal For A/C Compressor Regulator Valve -N280-, Checking
- Switch off ignition.







- Unplug connector at air-conditioner compressor.
- Use adapter cable from adapter set V.A.G 1594 A to re-establish connection between connector -A- and connector -B- at regulating valve.

NOTE:
- A/C Compressor Regulator Valve -N280- actuation and current measured by Climatronic Control Module -J255- flowing across A/C Compressor Regulator Valve -N280- are indicated in measured value block of Climatronic Control Module -J255- (display group 001).







- Use can also be made of an improvised adapter cable for this test. This requires, for example, one connector -A- and -B- each (with part number 1J0 973 702 and 1J0 973 802 and the corresponding plug contacts), two commercially available sockets for banana plugs -C- and two wires with a cross-section of 0.5 sq. mm.







- Connect DSO measuring leads VAS 5051/8 to adapter leads:
- Test lead (signal wire) to contact -2-
- Test lead (screen, Ground (GND)) to contact -1-
- Set measurement mode: DSO (Digital Storage Oscilloscope) on VAS 5051.
- Settings 5 V/div DC, 0.5 ms/div (5 V DC and 0.5 milliseconds per unit)
- Start engine.
- Pre-select "Lo" temperature on Climatronic Control Module -J255-.
- Switch actuation of A/C Compressor Regulator Valve -N280- on and off at Climatronic Control Module -J255- by pressing "Auto" and "Off/On" buttons.

The following will be indicated on oscilloscope screen depending on setting on Climatronic Control Module -J255-:
- "OFF" mode
No square-wave signal (regulating valve not actuated)







- "Auto" mode with temperature setting "Lo"
Square-wave signal with pulse width -A- between 75% and 100% (regulating valve actuated)

NOTE:
- The Fig. shows a signal with a duty cycle of approx. 80%.
- Pulse width -A- is governed, for example, by desired cooling output and vehicle electrical system voltage (over the width of range -A- current is controlled via A/C Compressor Regulator Valve -N280- by Climatronic Control Module -J255-).
- Signal distance -B- is always 2 milliseconds (corresponding to a frequency of 500 Hertz).
- Duty cycle results from ratio of pulse width -A- to signal distance -B-.

- Pulse width of square-wave signal varies as a function of setting on Climatronic Control Module -J255- and ambient influences measured (duty cycle between 100% and greater than 30%; regulating valve is actuated such that compressor output required to achieve specified temperatures is attained).

NOTE:
- In "Auto" mode with temperature setting "Lo", A/C Compressor Regulator Valve -N280- is actuated such that max. perm. current of approx. 0.65 A flows via A/C Compressor Regulator Valve -N280- (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.