Pressures For Vehicles With Expansion Valve, Receiver and A/C Compressor Regulator Valve N280
Pressures For Vehicles With Expansion Valve, Receiver And A/C Compressor Regulator Valve N280 (with Externally Regulated Compressor)
NOTE:
- Connecting service station. Pressures, Checking on Vehicles
- Observe test conditions. Pressures, Checking on Vehicles
- 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 percent)
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.
- 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:
- 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 .
