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Continuation of testing depending on design of refrigerant circuit > < Test requirements

A4 Mk1

Checking pressures
Checking pressures
t  Observe test requirements → Chapter.
–  Switch off ignition.
–  Connect air conditioner service station → Chapter.
–  Read pressures off pressure gauges; there are two possible results:
t  The pressure in the refrigerant circuit is lower than indicated in the table.
t  The pressure in the refrigerant circuit corresponds to that indicated in the table or is higher.
   
Ambient temperature (in degrees centigrade) Pressure in refrigerant circuit in bar
+15 °C3.9
+20 °C4.7
+25 °C5.6
+30 °C6.7
+35 °C7.8
+40 °C9.1
+45 °C10.5

  Note
t  Temperature of refrigerant circuit components should be equal to ambient temperature (the pressure will deviate from the values in the table if individual components of the refrigerant circuit are warmer or colder).
t  On the absolute pressure scale, 0 bar corresponds to an absolute vacuum. The 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).
t  On vehicles with a high-pressure sender -G65- or refrigerant pressure and temperature sender -G395- for which the measured pressure is displayed in the measured value block, the pressure measured should coincide with the values in the table → Vehicle diagnostic tester („self-diagnosis“ or „Guided Fault Finding“ function for air conditioner) and → Heating, air conditioning; Rep. gr.87 or → Air conditioning; Rep. gr.87 (vehicle-specific workshop manual).
t  Pressure can be measured in various units: 1 MPa (megapascal) is equivalent to 10 bar gauge pressure, or 145 psi; 1 bar absolute pressure is the same as 0 bar gauge pressure, which is roughly equivalent to atmospheric pressure.
The pressure in the refrigerant circuit is lower than indicated in the table.
Not enough refrigerant in circuit
–  Determine refrigerant circuit leaks → Chapter.
–  Check high-pressure safety valve.
If the high-pressure safety valve has blown off:
–  Check actuation of the radiator fans.
–  Check for constricted refrigerant line and hose cross-sections caused by inadequate bending radii.
–  Check refrigerant pipes and hoses for external damage.
–  If no fault is found, clean refrigerant circuit (flush with refrigerant R134a → Chapter or blow out with compressed air and nitrogen → Chapter).
The pressure in the refrigerant circuit corresponds to that indicated in the table or is higher.
–  Start engine.
–  Set air conditioning system to maximum cooling output.
  Note
On vehicles with an air conditioner compressor regulating valve -N280-, the control current can be read out in the measured value block → Vehicle diagnostic tester („self-diagnosis“ or „Guided Fault Finding“ function for air conditioner) and → Heating, air conditioning; Rep. gr.87 or → Air conditioning; Rep. gr.87 (vehicle-specific workshop manual).
If the air conditioner compressor is not driven when the engine is running or the regulating valve is not actuated:
–  Establish and eliminate the cause e.g. by interrogating the air conditioner event recorder.
–  Observe test requirements.
–  Check the power supply for the air conditioning system magnetic clutch -N25-. If this is OK, service the magnetic clutch.
–  Check actuation of the air conditioner compressor regulating valve -N280- → Vehicle diagnostic tester („self-diagnosis“ or „Guided Fault Finding“ function for air conditioner) and → Heating, air conditioning; Rep. gr.87 or → Air conditioning; Rep. gr.87 (vehicle-specific workshop manual).
  Note
t  If the low-pressure switch has been removed to connect the air conditioner service station, jumper the electrical connections in the relevant connector for pressure measurement.
t  The air conditioner compressor is driven by the engine via the air conditioning system magnetic clutch -N25-.
t  The air conditioner compressor regulating valve -N280- is actuated by the operating and display unit for Climatronic air conditioning system -E87- or the Climatronic control unit -J255- → Vehicle diagnostic tester („self-diagnosis“ or „Guided Fault Finding“ function for air conditioner) and → Heating, air conditioning; Rep. gr.87 or → Air conditioning; Rep. gr.87 (vehicle-specific workshop manual).
t  Continuation of testing depending on design of refrigerant circuit → Chapter
   

Continuation of testing depending on design of refrigerant circuit > < Test requirements