Pressures For Vehicles With Expansion Valve, Receiver and A/C Compressor Regulator Valve N280 (Externally Regulated)
Pressures For Vehicles With Expansion Valve, Receiver And A/C Compressor Regulator Valve N280 (with Externally Regulated Compressor)
NOTE:
- Connecting service station
- Observe test conditions. Component Tests and General Diagnostics
- Set engine speed to 2000 rpm.
- Observe pressure gauge of service station.
NOTE:
- Switching pressures for actuation of A/C Compressor Regulator Valve and Coolant Fan V7 are vehicle-specific.
- Pressures must be measured at service connections; component locations of these connections are vehicle-specific Heating, air conditioning or Air conditioning.
Specifications
High-pressure side:
Increasing from initial pressure (on connecting pressure gauges) to max. 20 bar
Low pressure:
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 in amps
C Permissible tolerance range (applicable to compressor capacity utilization of 10...90%)
NOTE: Given high ambient temperature and a low engine speed, compressor may for example no longer be able to adjust pressure on low-pressure side to value given in graph. Compressor is actuated with maximum specified control current, however delivery volume is no longer sufficient at this engine speed to reduce pressure on low pressure side to value in graph, air conditioner "Guided Fault Finding" function and Heating, air conditioning or Air conditioning.
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 of A/C Control Head E87 or Climatronic Control Module J255.
- High pressure measured by High Pressure Sensor G65 or A/C Pressure/temperature Sensor G395 is displayed in measured value block of A/C Control Head E87 or control head, Climatronic Control Module J255.
- Low pressure settles as a function of control current for A/C Compressor Regulator Valve N280 and control characteristic of expansion valve within compressor output range in tolerance band.
- Under unfavorable conditions (very high ambient temperatures, high humidity), compressor output may not always be sufficient to attain the specified value.
- If compressor capacity utilization is greater than 90 %, pressure on low-pressure side may be in excess of tolerance range "C" shown in graph (compressor output no longer suffices).
- Specified operating current for A/C Compressor Regulator Valve N280 must be greater than 0.3 A to ensure reliable valve actuation.
- In "maximum cooling output" setting, control current for A/C Compressor Regulator Valve N280 is regulated to approx. 0.65 A (up to 0.85 A). This measured value is vehicle-specific and displayed in measured value block.
- At absolute pressure, 0 bar corresponds to an absolute vacuum. Normal ambient pressure corresponds to 1 bar absolute. On the scales of most pressure gauges, 0 bar corresponds to an absolute pressure of 1 bar (can be seen from -1 bar mark below 0), air conditioner "Guided Fault Finding" function and Heating, air conditioning or Air conditioning.
NOTE:
- If no fault 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 actuation of A/C Compressor Regulator Valve N280. If measured value of Evaporator Vent Temperature Sensor G263 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, re-install old expansion valve and flush refrigerant circuit with compressed air and nitrogen. Then replace compressor and receiver.
- With this fault, 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, air conditioner "Guided Fault Finding" function and Heating, air conditioning or Air conditioning.
NOTE:
- If the function of the air conditioning system is not OK when the test is repeated, replace expansion valve and receiver.
- With this fault, 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, air conditioner "Guided Fault Finding" function and Heating, air conditioning or Air conditioning.
- If there is too much refrigerant oil in the circuit, drain compressor and replace receiver. After flushing refrigerant circuit, add correct amount of refrigerant oil to circuit.
NOTE:
- It is not initially necessary to flush the refrigerant circuit with compressed air and nitrogen when this problem occurs. Normally, there is only a small quantity of moisture in the system which can be removed by lengthy evacuation.
- 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.
- With this fault, evaporator may ice up although quantity of refrigerant in circuit is OK.
- Problem with Evaporator Vent Temperature Sensor G263 can also cause icing-up of refrigerant circuit. If this problem is encountered, also pay attention to measured value of Evaporator Vent Temperature Sensor G263, air conditioner "Guided Fault Finding" function and Heating, air conditioning or Air conditioning.
NOTE:
- Pay attention to the following as regards fault "High pressure normal, low pressure too low": This fault may cause the evaporator to ice up although the amount of refrigerant in the circuit is OK.
- If the problem is with the A/C Compressor Regulator Valve N280 (regulator 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 (pay attention to 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 refrigerant cannot however flow via expansion valve, cooling output is not attained and high pressure may either not increase or only slightly due to the absence of energy conversion.
- Check measured values of Evaporator Vent Temperature Sensor G263 and actuation of A/C Compressor Regulator Valve N280. If measured value of Evaporator Vent Temperature Sensor G263 is incorrect, evaporator may ice up or cooling output is not attained, air conditioner "Guided Fault Finding" function and Heating, air conditioning or Air conditioning.
NOTE:
- This fault may also be caused by too much refrigerant in the circuit. Overfilling with refrigerant may occur if, for example, the compressor has been replaced without adjusting the quantity of refrigerant oil.
- 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, air conditioner "Guided Fault Finding" function and Heating, air conditioning or Air conditioning.
NOTE:
- Overfilling with refrigerant oil may 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).
- If there is too much refrigerant oil in the circuit, drain compressor and replace receiver. After flushing refrigerant circuit, add correct amount of refrigerant oil to circuit.