Flushing lines on a mini split - R410a to R22
 

Hi all,
In a previous post I was experimenting with propane in a R410 mini split which had lost its gas due to a pipe fracture. To cut a long story short, it was not the most efficient and because its hard (and expensive!) to buy R410 in Australia I have gone and bought an R22 unit off eBay.
To make sure any old oil and crud is not left in the pipes it is best practice to flush the lines.... There are commercial flush fluids available but in the past I have used mineral spirits (Shellite) in automotive A/C to flush system components with no problems. Question: does R22 use mineral oil like old car R12 sytems? Not sure the date of manufacture, possibly 4-5 years old..but never installed.
Thanks,
James.

POE is OK in a R22 system. Mineral oil in a HFC system is OK as long as it's less than 5% or so of the total oil capacity. If there's other junk to get rid of, nitrogen is the way to go, but an air duster can (really R152a) is a good substitute for a one off.

Thanks for the tip!
I also note that some people have used it to regas their old R12 auto systems as well,
but if it gets out and sprays on your exhaust manifold I have read it can be rather toxic...

James,

First of all, I would like to thank you for reporting back about your experience in trying to convert a R410a system to R290. The fact that it was not a successful swap is very important information, because there has been a blizzard of speculation that it should work. Your experience that it did not work is useful to all of us here... hopefully it will stop the blizzard of B.S.

If your intention is to take an R22 system and switch it to R290, it is one of the easiest transitions possible.

R22 systems use mineral oil, in a hermetically sealed environment.

If your unit will work, and if it gets properly cold, it is still hermetically sealed.

R22 systems use mineral oil. R290 is perfectly compatible with mineral oil.

Your comment about gunk in the system does not apply to a hermetically sealed system, because there will not be any water or oxygen to contaminate the internal fluids. It is not at all like a car engine, so worries about gunk do not apply.

I wouldn't advise using anything other than mineral oil in your system. Mineral oil is great stuff, it's not as likely to aggressively absorb moisture like POE, and if it has been left open to atmosphere, you stand a possibility of being able to remove moisture by creating a long, deep vacuum with a good vacuum pump.

When you open your system, use a piercing valve and open it very, very slowly (be prepared to take a half hour or more... yes, THAT slow) and you stand a good chance of retaining all of your oil... it will be the right kind of oil, and it will be the right amount of oil, unless your hack radically changes the internal volume of your system.

I put two Brazed Plate heat exchangers on a dehumidifier and they replaced two smallish air coils. So I certainly changed the volume of my system, but I experienced no adverse effects. It ran just fine.

BradC, a fellow countryman of yours, had a lot of first rate experience with hacking heat pumps. It would be worth your time to search out his posts on this forum. He is very knowledgeable in these issues. Haven't heard from him in a while, but he definitely knows.

Let us know how it goes for you.

Take lots of photos!

Best,

-AC_Hacker

Because the unit is new I will use the R22 charge in it - I am re using the lines that I had the old R410a system on . just wanted to ensure the lines were clean before I put the new
R22 system together.. My question regarding the type of comp oil was because I have previously used "Shellite" as a flush fluid which is a fast evaporating mineral spirit on auto AC R12 systems. But the advice on the air duster/R152a looks like the way to go.

Sorry to say, but pretty much all of the "commonly accepted" refrigerants are this way. The refrigerants that are not highly flammable are that way because of added fluorine and/or chlorine in the molecule. When broken down by spark or flame, poison gases are liberated. If not broken down, the whole molecules eat at the ozone layer.

Lots of "historical" refrigerants have been shunned because they are just so poisonous. Examples:

Sulphur dioxide
Chloroform
Ether
Carbon Tetrachloride
Methylene Chloride

And then there's ammonia, which is still often used in industrial applications.

The whole flammability issue is way overstated for smaller systems. The oil used makes all refrigerants flammable. Moreover, the HVAC techs seem to have nothing against similarly flammable lithium batteries. It's a conspiracy by the fluorocarbon industry.

I don't recall that you actually spelled outy what it is that you are trying to do here?

You do know that when you braze HVAC copper lines, that you need to flood them with an oxygen and water free gas, right? If you don't, you will get tiny copper-oxide flakes that can plug your metering device later.

So, what are you doing with all your components?

-AC

You can also purge them with liquid propane as long as you are venting it to a safe area. We use a solvent called Citrol to clean resin from hoist chains. It is about 30% propane/isobutane - comes out of the spray can as liquid. The flashing of the propellant alone seems to boil off just about anything oil-based.

AC is correct, however, in that you still should have nitrogen in the lines when you braze them to avoid oxidation. Cap tubes and TEV's don't handle the flakes very well.

OP stated he is reusing his existing lineset, retrofitting from 410a to 22 split unit.

You can use just about any organic solvent, as long as it doesn't leave any residue. My favorite is brake parts cleaner, followed closely by acetone. I do this a lot with cars also. Almost every car I have ever flushed has the black death in it, whether or not the compressor survived. I honestly don't see how auto a/c systems can run for so long being so contaminated.

The most important part of the retrofit process is pulling a DEEP vacuum on the indoor unit and lineset. Use a micron gage. Make sure it holds vacuum at as low a micron reading as you can pull.