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Cleaning refrigerant circuit with refrigerant R134a (flush) > < Removing contaminants from the refrigerant circuit

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Cleaning the refrigerant circuit with compressed air and nitrogen
   
Cleaning the refrigerant circuit with compressed air and nitrogen
In order to remove impurities as well as aged refrigerant oil in a clean refrigerant-saving and environmentally friendly manner, without demanding installation, the refrigerant circuit is flushed out with refrigerant R134a or is blown through with compressed air and nitrogen.
  Note
Blowing through the refrigerant circuit with compressed air and nitrogen requires considerably more work than flushing with refrigerant R134a. When flushing with refrigerant R134a, the cleaning of the components is better and more effective, one should therefore always flush if there is a problem.
The refrigerant circuit or the individual components must be blown through first with compressed air and then with nitrogen, if:
t  it is not possible to flush the refrigerant circuit with the refrigerant R134a.
t  dirt or other impurities has/have entered into the circuit.
t  when evacuating a tight refrigerant circuit the vacuum gauge is not constant (there is humidity in the refrigerant circuit which builds up pressure).
t  the refrigerant circuit was open beyond standard assembly time (e.g. after an accident).
t  pressure and temperature measurements indicate that there is humidity in the refrigerant circuit.
t  There is any doubt about the oil volume in the refrigerant circuit.
t  the compressor needed to be replaced because of internal damage (in this case it is preferable to flush with refrigerant R134a → Chapter).
t  required after replacing one of the components of the Workshop Manual.

   
Blowing through the refrigerant circuit
  WARNING
t  Nitrogen may leak uncontrollably from the bottle.
t  Only work with reduction valve for nitrogen cylinders (maximum working pressure: 15 bar).
t  The gas mixture emanating from the components must be exhausted via a suitable exhaust system.
  Note
t  To ensure neither oil nor moisture is transferred from the compressed-air system into the refrigerant circuit, the compressed air must be led through a compressed-air cleaning system for cleaning and drying. For this use a filter and dryer for compressed air (scope of delivery as tool for paint work).
t  The maximum working pressure when blowing through must not be greater than 15 bar, (if necessary also use a pressure reducer for compressed air).
t  Use a suitable adapter to connect the pressure hose to the refrigerant circuit.
t  The adapters must not damage the components of the refrigerant circuit.
t  Remove the fluid reservoir with dessicator before blowing through the condenser (if possible).
t  The evaporator must be blown through via the low-pressure line connection (large diameter) once the expansion valve or the throttle has been removed.
t  Check expansion valve, replace if corroded or dirty.
t  If there are dark, sticky deposits in the components that cannot be removed with compressed air, replace these components.
t  Thin, light grey deposits on the inside do not hinder the operation of the components.
t  Compressed air and nitrogen cannot be blown through the compressor and the expansion valve or the throttle.
t  Always blow through the components against the flow direction of the refrigerant.
Work procedure
–  Connect the changed filling hose with suitable adapters to the workshop compressed air system and connect the component to be blown through.
–  Switch on the exhaust system and vacuum impurities and refrigerant oil with the suction hose.
–  First blow through old refrigerant oil and dirt with compressed air.
–  Blow through components with compressed air until no more dirt and refrigerant oil is expelled (e.g. check with absorbant paper or a white cloth).
–  Connect the reduction valve with the nitrogen pressure hose to the nitrogen cylinder and „dehumidify“ the individual components with nitrogen using the nitrogen pressure hose and the relevant adapters (exhaust system must be on).
–  Replace the AC compressor or unscrew the drain plug from the removed AC compressor (replace O-ring → Electronic Catalogue of Original Parts) and drain the remaining refrigerant oil. In order to speed up the evacuation of the refrigerant oil, turn the AC compressor with the clutch disk of the magnetic coupling by hand (disposal of used oil → Chapter). Subsequently fill the volume of new refrigerant oil, which corresponds to the refrigerant oil volume in the original part AC compressor, into the removed AC compressor → Heating, Air Conditioning → Rep. gr.87.

  Note
t  Draining off the oil from the compressor is only possible through the filling opening, the compressor must therefore be removed.
t  Once no more refrigerant oil runs out of the compressor; turn on the compressor by hand and drain off residual oil.
Replace the fluid reservoir with dessicator insert whenever the refrigerant circuit has been blown through and keep it closed as long as possible to prevent insofar as possible any humidity from penetrating into the dessicator insert.
   

Cleaning refrigerant circuit with refrigerant R134a (flush) > < Removing contaminants from the refrigerant circuit