Pressure Checking, Vehicles With Restrictor, Reservoir and Externally Regulated Compressor
Pressure Checking, Vehicles With Restrictor, Reservoir And A/C Compressor Regulator Valve With Externally Regulated Compressor
NOTE:
- Connecting A/C service station
- Observe test conditions.
- Set engine speed to 2000 rpm.
- Observe pressure display (e.g. pressure gauge) of A/C service station.
NOTE:
- Switching pressures for actuation of A/C Compressor Regulator Valve N280 and Coolant Fans V7 are vehicle-specific.
- Pressures must be measured at service connections; component locations of these connections are vehicle-specific.
Specifications
High-pressure side:
Increasing from initial pressure (on connecting pressure gauges) to max. 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.
- 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.
- 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.
NOTE: If no fault is found with this complaint, clean refrigerant circuit (flush using refrigerant R134a or blow through using compressed air and nitrogen).
NOTE:
- It is not initially necessary to clean the refrigerant circuit (flush using refrigerant R134a or blow through using 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.
- 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.
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.
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, the compressor must be drained and the receiver must be replaced. After cleaning the refrigerant circuit (flushing with refrigerant R134a or blowing through using compressed air and nitrogen), the correct quantity of refrigerant oil is filled into the circuit.