Q - increasing copper tubing size

Old 07-15-11, 12:05 PM
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Q - increasing copper tubing size

Q: Can I just increase copper tubing size? Increase in tubing size means more R22 in the system. Will I have to use larger accumulator?

Background: I have 2 2-ton AC RHEEM 10 SEER. 10 years old. Original copper tubings (25+- years old). 1/4" (or 5/16") supply. Return line not sure.

The downstairs unit developed a leak and repairman put in new copper. He said one size up. 5/8" I believe. I get a much better cooling. Now I am convinced I need to increase the copper size for the upstairs unit.

Downstairs unit has only 20-25' copper, horizontal. Upstairs unit goes vertical 20' and horizontal 20'. The repairman recommends 1 size up for supply and 2 sizes up for return.

Old 07-15-11, 01:18 PM
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Not a HVAC person, they will show up later - after work.
I don't quite understand the logic here. You could use 6" piping and it would still neck down to the fitting size on each end.

Ten year old units probably have five years left. When you upgrade to the new freon units, you will probably have to toss the old piping along with the "A" coil.
Old 07-15-11, 02:41 PM
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Increasing the tubing size will under certain circumstances increase the refrigerant flow but it will also decrease the velocity. Decreased velocity makes it much more likely that oil will pool in the return line rather than return to the compressor. Larger lines would certainly require more refrigerant and possibly a larger accumulator.

I do not recommend changing line sizes without affirmation from the equipment manufacturer.
Old 07-15-11, 06:54 PM
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Thanks for the replies. Subcooling/superheat not sufficient with current 5/16" line. The repairman is telling the truth. I need to up the size. I will check with manufacturer for proper sizing. Thanks.

I asked the same question to the repairman - if I put in a new line, will I lose it when I switch from R22 to R410. He said he could chemically flush the old line. Please clarify. Thanks.
Old 07-15-11, 08:16 PM
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yes, can flush, but dont recommend if replaceable. There is no way to know if the pipe is completely cleaned out.
Old 07-16-11, 05:33 AM
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When dealing with line sizing on residential a/c you have to follow mfr's recommendations for your specific unit!
In fact, one mfr of mini-split units changed the design of their units to allow longer line lengths and the supplier's "expert " did not know this.

Because there is no refrigerant storage device the liquid line serves the purpose of refrigerant storage and on some units becomes part of the metering device.
It is possible to have too much refrigerant in the system which in certain cases can either cause too high a head pressure due to a lack of storage or compressor damage due to off cycle migration, even with a working crankcase heater if there is on on your system.

Many newer systems require smaller lines that what was common years ago and what at one time was undersized may not be today.
Also, when installing a new system you would do well to replace all the lines even if the tech says they will be good.
Could be they are sized properly or could also be the installer wants to do a fast job!

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