With Expansion Valve, Reservoir and A/C Compressor Regulator Valve N280 (Externally Regulated Compressor), Checking
Checking With Expansion Valve, 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.
- The pressures should be measured at the service connections. The location of these connections is 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 measured from the High Pressure Sensor G65 is not 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. 0.65 A up to 0.85 A (vehicle specific, 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.
- Check measured values from Evaporator Vent Temperature Sensor G263 or Evaporator Temperature Sensor G308 and activation of A/C Compressor Regulator Valve N280. If the measured value of the High Pressure Sensor (365 is faulty, the evaporator can ice up or the cooling output is not reached.
- If the function of the air conditioning system is not OK when the test is repeated after replacing expansion valve, re-install old expansion valve and flush refrigerant circuit with compressed air and nitrogen. Then replace A/C compressor and reservoir.
- With this malfunction, evaporator may ice up although quantity of refrigerant in circuit is OK.
- If expansion valve is malfunctioning (permanently closed or does not open sufficiently), A/C Compressor Regulator Valve N280 is actuated to maximum output and low pressure drops to value in graph or below (compressor draws off refrigerant from low-pressure side). As however refrigerant cannot flow via expansion valve, cooling output is not attained and high pressure may also not increase or only increase slightly due to the absence of energy conversion.
NOTE:
- With this malfunction, evaporator may ice up although quantity of refrigerant in circuit is OK.
- If expansion valve is malfunctioning (permanently closed or does not open sufficiently), A/C Compressor Regulator Valve N280 is actuated to maximum output and low pressure drops to value in graph or below (compressor draws off refrigerant from low-pressure side). As however refrigerant cannot flow via expansion valve, cooling output is not attained and high pressure may also not increase or only increase slightly due to the absence of energy conversion.
NOTE:
- If this complaint occurs after a long operating time or only sporadically (the low pressure falls under the specified value and the evaporator ices up), replacing the dryer (installed in the reservoir) is sufficient. The quantity of refrigerant oil should be adjusted. Refrigerant circuit is then to be evacuated for at least 3 hours.
- First, it is not necessary to flush the refrigerant circuit with compressed air and nitrogen in case of this complaint because generally only a small amount of moisture is in the system and this can be removed by a long evacuation.
- With this malfunction, evaporator may ice up although quantity of refrigerant in circuit is OK.
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 from Evaporator Vent Temperature Sensor G263 or Evaporator Temperature Sensor G308 and activation of A/C Compressor Regulator Valve N280. If the measured value of the High Pressure Sensor G65 is faulty, the evaporator can ice up or the cooling output is not reached.
- If the problem is with the A/C Compressor Regulator Valve N280 (regulating valve is not actuated but compressor operates nevertheless), refrigerant circuit does not have to be flushed. With this malfunction, replacing the A/C compressor is sufficient (adjust refrigerant oil quantity in new A/C compressor).
- If expansion valve is malfunctioning (permanently closed or does not open sufficiently), A/C Compressor Regulator Valve N280 is actuated to maximum output and low pressure drops to value in graph or below (compressor draws off refrigerant from low-pressure side). As however refrigerant cannot flow via expansion valve, cooling output is not attained and high pressure may also not increase or only increase slightly due to the absence of energy conversion.
NOTE:
- If the problem is with the A/C Compressor Regulator Valve N280 (regulating valve is not actuated but compressor operates nevertheless), refrigerant circuit does not have to be flushed. With this malfunction, replacing the A/C compressor is sufficient (adjust refrigerant oil quantity in new A/C compressor).
- 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.
- If expansion valve is malfunctioning (permanently closed or does not open sufficiently), A/C Compressor Regulator Valve N280 is actuated to maximum output and low pressure drops to value in graph or below (compressor draws off refrigerant from low-pressure side). As however refrigerant cannot flow via expansion valve, cooling output is not attained and high pressure may also not increase or only increase slightly due to the absence of energy conversion.
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.
- If expansion valve is malfunctioning (permanently open), evaporator temperature is no longer regulated such that only refrigerant in gaseous state exits from the evaporator. Under certain usage conditions, liquid droplets may then be drawn in by the compressor and cause noise (liquid cannot be compressed).