Audi A4: Vehicles with Restrictor, Reservoir and A/C Compressor Regulator Valve -N280- (Externally Regulated A/C Compressor), Checking Pressures

Specified Values for the Refrigerant Circuit Pressures

  Note

• Connect the Air Conditioning (A/C) service station. Refer to → Chapter "A/C Service Station, Connecting".
• Observe the test requirements. Refer to → Chapter "Pressures, Checking".

- With the ignition switched off, check the pressure in the refrigerant circuit (using the service station). Refer to → Chapter "Refrigerant Circuit, Checking Pressure with Service Station".

The pressures with the ignition turned off meet the specifications.

- Start the engine.

- Bring the engine speed up to 2000 RPM.

- Observe the pressure gauge of the service station.

  Note

• The switch pressures for the A/C A/C Compressor Regulator Valve -N280- and the Coolant Fan -V7- are vehicle specific.
• Pressures must be measured at service connections; component locations of these connections are vehicle-specific. Refer to → Heating, Ventilation and Air Conditioning; Rep. Gr.87; System Overview - Refrigerant Circuit (vehicle-specific repair manual).

High-Pressure Side:

Increasing from initial pressure (when connecting pressure gauges) to 20 bar (290 psi).

Low-Pressure Side:

Decreasing from initial pressure (when connecting pressure gauges) to the value in the graph.

A - Low pressure (measured at service connection) in bar (psi)

B - Control current for A/C Compressor Regulator Valve -N280- in amps.

C - Permissible tolerance range

  Note

• If high cooling output is needed (for example, the outside temperature is very high, the blower speed it set on high but the engine RPMs are low), then the A/C compressor will not bring the pressure on the low pressure side to the value specified in the diagram -C- (for example, for a certain time after turning on the A/C). The A/C 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. To check the A/C compressor control under these conditions, for example, the fresh air blower is controlled only with approximately 40% of the maximum voltage, check the pressures at a lower fresh air blower speed. Use the Vehicle Diagnostic Tester ("OBD" or "Guided Fault Finding for the A/C system") and → Heating, Ventilation and Air Conditioning; Rep. Gr.00; Repair Instructions; Checking Cooling Output or →Heating, Ventilation and Air Conditioning; Rep. Gr.87 (vehicle-specific repair manual).
• Under unfavorable conditions (very high ambient temperatures, high humidity), pressure on high-pressure side may increase up to maximum 29 bar (421 psi).
• Control current -B- is displayed in measured value block of A/C Control Head -E87- or control head, Climatronic Control Module -J255-.
• The measured pressure from the High Pressure Sensor -G65- or from the A/C Pressure/Temperature Sensor -G395- inside the refrigerant circuit pressure is displayed in the measured values block for the Front A/C Display Control Head -E87- and the Climatronic Control Module -J255- ("OBD" or "Guided Fault Finding for the A/C System") and → Heating, Ventilation and Air Conditioning; Rep. Gr.87; System Overview - Refrigerant Circuit (vehicle-specific repair manual).
• 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.
• 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 sufficient).
• The specified operating current for the regulator valve must be greater than 0.3 A in order to ensure reliable valve activation.
• At absolute pressure, "0 bar/psi" corresponds to absolute vacuum. Normal ambient pressure corresponds to 1 bar (14.5 psi) absolute pressure. 0 bar/psi pressure corresponds to an absolute pressure of 1 bar (14.5 psi) on most pressure gauges (indicated by "-1 bar (-14.5 psi)" below "0").
• In "maximum cooling output" setting , control current is regulated to approximately 0.65 (vehicle-specific up to 0.85A, displayed in measured value block). Use the Vehicle Diagnostic Tester ("OBD" or "Guided Fault Finding for the A/C System") and → Heating, Ventilation and Air Conditioning; Rep. Gr.00; Repair Instructions; Checking Cooling Output or →Heating, Ventilation and Air Conditioning; Rep. Gr.87 (vehicle-specific repair manual).

  Note

If no fault is found with this malfunction, clean the refrigerant circuit (flush using refrigerant R134a. Refer to → Chapter "Refrigerant Circuit, Cleaning (Flushing), with Refrigerant R134a"; or blow through using compressed air and nitrogen. Refer to → Chapter "Refrigerant Circuit, Flushing with Compressed Air and Nitrogen").

  Note

• It is not initially necessary to clean the refrigerant circuit (flush using refrigerant R134a. Refer to → Chapter "Refrigerant Circuit, Cleaning (Flushing), with Refrigerant R134a" or blow through using compressed air and nitrogen. Refer to → Chapter "Refrigerant Circuit, Flushing 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.
• 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 three 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-. Use the Vehicle Diagnostic Tester ("OBD" or "Guided Fault Finding" for the A/C System) and → Heating, Ventilation and Air Conditioning; Rep. Gr.00; Repair Instructions; Checking Cooling Output or →Heating, Ventilation and Air Conditioning; Rep. Gr.87 (vehicle-specific repair manual).

  Note

For the malfunction "high pressure normal, low pressure too low", note the following: With this malfunction, evaporator may ice up although the quantity of refrigerant in circuit is OK. Check measured values of the Evaporator Vent Temperature Sensor -G263- and the actuation of the A/C Compressor Regulator Valve -N280-. If the measured value from the Evaporator Vent Temperature Sensor -G263- is incorrect, the evaporator may ice up or cooling output is not attained Vehicle Diagnostic Tester ("OBD" or "Guided Fault Finding for the A/C System") and → Heating, Ventilation and Air Conditioning; Rep. Gr.00; Repair Instructions; Checking Cooling Output or →A/C System; Rep. Gr.87 (vehicle-specific repair manual).

  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 accumulator must be replaced. After cleaning the refrigerant circuit (flushing with refrigerant R134a. Refer to → Chapter "Refrigerant Circuit, Cleaning (Flushing), with Refrigerant R134a"; or blowing through using compressed air and nitrogen. Refer to → Chapter "Refrigerant Circuit, Flushing with Compressed Air and Nitrogen"), the correct quantity of refrigerant oil is filled into the circuit. Refer to → Chapter "Approved Refrigerant Oils and Capacities".

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