With Restrictor, Reservoir and A/C Compressor Regulator Valve N280 (Externally Regulated Compressor), Checking

Checking With Restrictor, Reservoir And A/C Compressor Regulator Valve N280 (Externally Regulated Compressor)

NOTE:
- Connecting service station.
- Observe test requirements.

- Bring engine speed up to 2000 RPM.
- Observe pressure gauge of A/C service station.

NOTE: Switch pressures for activating the A/C Compressor Regulator Valve N280 and Coolant Fan V7 are vehicle-specific.

Specified values:

High-pressure side:
Increasing from initial pressure (on connecting pressure gauges) to 20 bar.

Low-pressure side:







Decreasing from initial pressure (on connecting pressure gauges) to value in graph.
A - Low pressure (measured at service connection) in bar absolute
B - Control current for A/C Compressor Regulator Valve N280.
C - Permissible tolerance range

NOTE:
- Under unfavorable conditions (very high ambient temperatures, high humidity), pressure on high-pressure side may increase to max. 29 bar.
- The control current -B- is shown in the measured value block.
- The high pressure is shown in the measured value block.
- Low pressure settles as a function of control current for A/C Compressor Regulator Valve N280 within compressor output range in tolerance range.
- Under unfavorable conditions (very high ambient temperatures, high humidity), compressor output may not always be sufficient to attain the specified value.
- The specified operating current for the regulator valve must be greater than 0.3 A in order to ensure reliable valve activation.
- In the setting "maximum cooling output" control current is regulated to approx. 0.8 A (displayed in measured value block).
- At absolute pressure, 0 bar corresponds to absolute vacuum. Normal ambient pressure corresponds to 1 bar absolute pressure. 0 pressure corresponds to an absolute pressure of one bar on most pressure gauges (indicated by -1 bar below 0).







NOTE: If no malfunction is found with this complaint, flush (clean) refrigerant circuit with refrigerant R134a. If that is not possible in this workshop, flush refrigerant circuit with compressed air and remove moisture with nitrogen.










NOTE:
- For the malfunction "high pressure normal, low pressure too low", note the following: faulty, the evaporator can ice up or the cooling output is not reached.
- With this malfunction, evaporator may ice up although quantity of refrigerant in circuit is OK.
- Check measured values of Evaporator Vent Temperature Sensor G263 or Evaporator Temperature Sensor G308.
- Check activation of A/C Compressor Regulator Valve N280







NOTE:
- Overfilling with refrigerant oil can occur if, for example, the compressor has been replaced without adjusting the quantity of refrigerant oil.
- If the A/C compressor is not replaced, the refrigerant oil should be drained from the A/C compressor via the drain plug (replace O-ring). Out of the entire quantity of refrigerant oil, 50 grams should be put in the A/C compressor and the rest in the refrigerant circuit.