Expansion Valve, Receiver and A/C Compressor Regulator Valve N280 (Externally Regulated Compressor), Checking
Expansion Valve, Receiver and A/C Compressor Regulator Valve N280 (Externally Regulated Compressor), Checking
NOTE:
- Connect service station. Working With Service Station
- Observe test conditions. Pressures In Refrigerant Circuit, Checking (Using Service Station)
- Set engine speed to 2000 RPM.
- Observe pressure gauge of service station.
NOTE:
- Switching pressures for actuation of A/C Compressor Regulator Valve N280 and Coolant Fan V7 are vehicle-specific.
- Pressures must be measured at service connections; component locations of these connections 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.
- Control current - B - is displayed in measured value block.
- High pressure measured by High Pressure Sensor G65 is displayed in 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 regulating valve must be greater than 0.3 A in order to ensure reliable valve actuation.
- 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 equals 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 in relation to this complaint, flush refrigerant circuit with compressed air and nitrogen.
- Check measured values of Evaporator Vent Temperature Sensor G263 and activation of A/C Compressor Regulator Valve N280. If measured value of High Pressure Sensor G65 is not OK, evaporator may ice up or cooling output is not attained.
- If the function of the air conditioning system is not OK when the test is repeated after replacing expansion valve, reinstall old expansion valve and flush refrigerant circuit with compressed air and nitrogen. Then replace A/C compressor and receiver.
- 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 problem involving moisture in refrigerant circuit only occurs after a lengthy operating period or only infrequently (low pressure drops below specification and evaporator ices up), it is sufficient to replace the dryer in the receiver Adjust quantity of refrigerant oil. Refrigerant circuit is then to be evacuated for at least 3 hours.
- It is not initially necessary to flush the refrigerant circuit with compressed air and nitrogen when this problem occurs since normally, there is only a small quantity of moisture in the system which can be removed by lengthy evacuation.
- With this malfunction, evaporator may ice up although quantity of refrigerant in circuit is 0K.
NOTE:
- For the malfunction "high pressure normal, low pressure too low", note the following: If malfunctioning, evaporator may ice-up or cooling output is not reached.
- With this malfunction, evaporator may ice up although quantity of refrigerant in circuit is 0K.
- Check measured values of Evaporator Vent Temperature Sensor G263 and activation of A/C Compressor Regulator Valve N280. If measured value of High Pressure Sensor G65 is not OK, evaporator may ice up or cooling output is not attained.
- 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. It is sufficient in this case to replace the compressor (adjust quantity of refrigerant oil in 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. It is sufficient in this case to replace the compressor (adjust quantity of refrigerant oil in 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:
- Overfilling with refrigerant oil can occur if, for example, the compressor has been replaced without adjusting the quantity of refrigerant oil.
- If expansion valve is malfunctioning (permanently open), evaporator temperature is no longer regulated such that only refrigerant in gas form 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).