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Question DetailsAsked on 7/18/2017

On CAC can new unit piping be downsized to fit old piping?

Have a 28 year old 4 ton unit that needs to be replaced. Installer said old piping could not acommadate new unit piping because of different size piping now being used

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1 Answer


Don't know what CAC is - unless you mean a Carrier Air Conditioning unit.

The "size" may relate to the flow capacity - i.e. the tubing diameter - many of the newer R-410a units need a higher gas flow to give the same cooling capacity, so say with normal short lineset you might need to upgrade from a 1/4" to 3/8" lineset, for instance - if that is the case, no getting around it. You do not want to use tubing which is undersized for the unit - installation manual should have required lineset sizing (measured by OUTSIDE diameter of the tubing, and not at any fittings) for different run length ranges.

Also, many R-410a units run a significantly higher pressure than Freon (R-22) units, so the old line may not be thick enough or high enough strength copper to handle the higher pressure.

If both of the above are within spec, then you could put in an adapter fitting - though every added fitting adds more potential leakage points.

Another problem - assuming your old unit is Freon (R-22) or perhaps even an older gas, the lubricant is most likely mineral oil - which does not get qalong at all well in R-410a units, and can cause sludging up in the lines - so while it is possible to flush the lines (and I would do two full cycles if that is the route you need to go), even if the existing lines are strong and large enough for the new unit, unless replacement is real tough (under slab or in walls for quite a ways) I would still go with the replacement route - not only to ensure your warranty cannot be cancelled (after the fact) by the manufacturer, but also jusat to be on the safe side. Things like contamination in the lubricant can really shorten the lift of your compressor, as well as gumming up the TXV valve. Plus good flushing might well run near as much ($500 range for normal 10-25' lineset) as just going ahead and installing a new lineset.

Personally, I would say you got a real good deal on the last unit, and I would be replacing the lineset regardless at that age, unless it is real hard to get to and means tearing out a bunch of drywall or siding to get at it to replace it AND there is no easy other way to route a new lineset.

Answered 3 years ago by LCD

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