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Question DetailsAsked on 10/29/2016

What do you use to flush out a AC line set of R22 when converting to R410A. I am replacing the compressor and evaps

I would like to re-use the copper tubing, but I don't know if I can either blow out the lines with compressed air or flush out with a solvent or should I run new lines?

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1 Answer


Here is a related similar answer which might help -

Unfortunately, not knowing what sort of oil you have in it, can't give any recommendation on the flushing compound - different types work with minearal oil (the common R-22 lubricant), others with POE polyester synthetic oils, others with ester oils, etc. About 7 or so different lubricants haqve been used by different manufacturers of A/C units and gases. Technically, the type of oil should be labelled on the manufacturer's label for the unit (sometimes on or at the compressor, sometimes in the housing) and if the gas and oil type were flushed out and changed at some point in the past, there is SUPPOSED to be a new label put on showing the oil type.

I would NOT use one of the "miracle do all" flushing compounds - many of them have acids or lye or sodium hydroxide (strong base) in them which can seriously damage the lineset, valves, compressor - or even dissolve the seals and gaskets. Try to find out what type of oil is in there (or I guess assume mineral oil if you and your tech can't figure it out) and use a flushing compound recommended by the manufacturer of the new compressor (for which theoil type is mnost critical of any component). And make sure the flushing is done BEFORE any new components are put in, not afterwards - I have seen systems that were rebuilt THEN flushed of the old material in the linesets, contaminating and damaging the new components.

And the dryer/filter cartridge must also be changed (not a substantial cost when done as part of the job) after the flush - because the mixture of oils and solvent and moisture is most likely to make an ungodly muck in there - I have seen it so thick and gummy that you turn it upside down and it just hangs there like peanut butter - does not flow out of the filter at all even though it is substantially full of lubricant and cleaner.

On reusing the lines - you need to check the ASTM standard the lines are rated to - some R-22 installations are done with high-pressure rated copper tubing, some with low - so some rated for R-22 use may not be able to safely take the higher R-410a pressure. And don't believe anyone who says only the high-side lines are important - if the filter plugs up, the TXV valve screws up, or soemtimes when the unit is sitting idle right after running at full temp in hot weather, the low-side pressure can be as high as the high-side - so ALL the components have to be rated for the higher pressure.

BTW - on the solvent or compressed air thing - compressed air will not move all the oil out, there will still be a film on the lines at least, as well as accumulations in compressor and valves and such - so it needs to be flushed with the proper solvent, then blown out with dry nitrogen. Compressed air is bad to use - first because commonly it has oil in the airstream unless it was HEPA filtered.. Also, the compressed air has moisture in it which can collect in the system, causing foaming and sludging of the oil - so not a good thing to blow the lines out with other than initial cleanout after cutting and installing them (to blow out any solder drips or other debris) BEFORE starting hooking the system up, which procedure includes drying and blowing out the lines with dry nitrogen (or with some A/C techs, the refrigerant gas though that is expensive and illegal).

Answered 3 years ago by LCD

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