Pressures, Checking For Vehicles With Restrictor, Reservoir and A/C Compressor Regulator Valve N280 (Externally Regulated)
Pressures, Checking For Vehicles With Restrictor, Reservoir 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 N280 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 connection of 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 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 control head, Climatronic Control Module J255.
- Pressure in refrigerant circuit 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 and Heating, air conditioning or Air conditioning.
- Low pressure settles as a function of control current for A/C Compressor Regulator Valve N280 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).
- The specified operating current for the regulator valve must be greater than 0.3 A in order to ensure reliable valve actuation.
- 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).
- In "maximum cooling output" setting, control current is regulated to approx. 0.65 (vehicle-specific up to 0.85 A) (displayed in measured value block), 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.
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 (adjust quantity of refrigerant oil). Refrigerant circuit is then to be evacuated for at least 3 hours.
- 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 lead to icing-up of evaporator although quantity of refrigerant in circuit is OK. 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:
- Overfilling with refrigerant oil can occur if, for example, the compressor has been replaced without adjusting the quantity of refrigerant oil.
- If there is too much refrigerant oil in the circuit, drain compressor and replace reservoir. After flushing refrigerant circuit, add correct amount of refrigerant oil to circuit.