Why flush an automotive air conditioning system?
Flushing is necessary to ensure that the system is clean and free of contamination to operate efficiently!
As one of our customers said (he must have been doing some painting in the holidays!) :
“ flushing a system is like putting an undercoat on!”
Remember that the TX valves (Thermostatic Expansion Valve) has a tiny orifice and almost sprays the liquid into the evaporator, so that the cooling effect takes place. (think of an aerosol can – and you have the idea) Any filing from a compressor failure can either block the TX valve or harm its operation. Obviously, it is ideal when replacing a compressor to replace a TX valve and we should be reminded that manufacturers such as Sanden and Denso insist on this being done every time that a compressor is replaced. Never back flush a TX Valve .
Evaporator coils are also critical to be flushed. Imagine a compressor failure and it pumps filings through the system and blocks the valve. As the compressor is failing any filings build up in the filter drier the compressor pumps until the AC system is cut off. The vacuum that is pulled in the suction side of the system means that all filings and oil in the compressor are sucked straight into the Evaporator coil! The result – and evaporator coil full of filings.
Condensers get the heat out of the system and lead to making that cool air blow out the vents. Remember any Modine or tube and fin condensers can be flushed but Parallel flow condensers like seen on most current vehicles can not be flushed and need replacing. The flush will simply take the easiest route and may miss many tubes leaving a lot of foreign material in the system.
Flushing is a good practice for any system not performing even if not replacing a compressor. When you don’t know the history of a system, you may have had a compressor replaced by another tech and not have a clean system. Over time an oil ‘sludge’ builds up and hinders cooling. A system additive, Hi-Cool helps to overcome this and has a lubricity agent in to help compressor run smoother, cooler and last longer.
Beware of oily flush solvents in the market place. These leave a residue that can affect oil viscosity and even lead to compressor failure down the track. Make sure you specify a TO-28729 flush when ordering. Try by dropping a finger in the top of the solvent and watch the oil even be dried off the end of your finger as it evaporates.
Always remember to give the system a good vacuum following with a 2 stage pump to avoid any flush being left in the system and make sure you use dry nitrogen to blow out. Any flush left will result in a hydraulic lock up in the compressor which we want to avoid at all costs!
FLUSHING PROCEDURE
1. Disconnect the receiver-drier or accumulator and discard.
2. Disconnect all hoses and lines and discard all o-rings.
3. Remove the TX valve or orifice tube and discard.
4. Using TO-28760 flush kit, or similar, inject flushing agent TO-28729 using dry nitrogen. (Do not use compressed air) in liquid form into evaporator, condenser and all hoses and lines. (Do not flush the compressor - see first note/helpful hint below).
5. Most technicians find it simplest to power flush the components. Alternatively, fill the component(s) with liquid solvent, cap off openings and leave for 5-10 minutes to allow oil, foreign material and any other contaminants to be dissolved and/or loosened.
6. All solvent vapour must be totally removed during evacuation. ‘Purging’ with dry nitrogen prior to evacuation may be necessary to achieve this.
7. For badly contaminated systems, repeat (4), (5) and (6) until no oil or foreign material is evident.
8. After repairs are completed, drain and renew oil charge, and renew all disturbed O-rings.
IMPORTANT: This is critical.
NOTES & HELPFUL HINTS FOR FLUSHING SYSTEMS
• Do not flush compressors when they are fitted. Flushing automotive air conditioning compressors with refrigerants or solvents is not normally recommended at all, and the following information may be useful.
• (i) most late model swash-plate or vane type compressors are not designed to be dismantled and some internal parts may not be available. In addition, re-assembly may not be possible without special equipment.
• (ii) for those models which can be dismantled such as the York or Tecumseh twin cylinder models, the compressor should be stripped, cleaned, and the oil charge renewed.
• (iii) most compressor manufacturers do not recommend flushing out compressors with solvent.
• Do not flush receiver-driers or accumulators - renew them.
• Always renew the oil with the correct oil charge for the system concerned.
• Never re-use refrigerant oil.
• All o-rings must be renewed if disturbed.
• TO-28729 can be re-used many times if impurities are removed. It is very stable chemically, and unless you are removing a heavy acid ontamination, filtration will remove most of the contaminants and leave it suitable for re-use as a solvent. A suitable in-line refrigeration filter can be used.
• Do not use your reclaim or reclaim/recycle equipment to reclaim or recycle solvents.
• Never mix refrigerants and/or solvents.
• Dry nitrogen is not a solvent. It will remove moisture effectively, but will not remove acid, corrosion, foreign material, excessive oil, etc. It is not a substitute for flushing.
• Keep containers capped when not actually in use.
• In no case should R134a be used to flush a system unless used with a closed type system such as a fully automatic charging machine.
• It is difficult, and sometimes impossible, to flush out components such as modine or parallel flow condensers if they are badly contaminated. Debris can be lodged in one or more tubes and be freed up later when the system is operating. Flushing is essential where contamination is suspected, but complete removal of foreign material cannot be guaranteed.