View Full Version : Flare nuts

04-07-2005, 10:56 PM
I carry out regular ppm on a vast range of equipment but never before have I came across the strange phenomenon of flare nuts cracking.Especially on air-con units.
The equipment I am referring to is of a well known manufacturer.The kit is 3 pipe vrf (R407C).
Every now & again during maintenance checks I will come across oil patches on ceiling tiles or fault codes initiated @ remote controllers.Upon inspection of fan coil (ducted type) it is always the 1/2" gas pipe flare that cracks, though on other occassions I have also found the 3/8" liquid line flare cracked on the c/h box. As you can imagine, the process for repairs on this kit is rather expensive and in turn the customers can become very irritated :mad:
I am sure that the manufacturer is aware of this problem as I have conversed with an engineer from their technical team whom had informed me of this type of problems on various sites in the u.k.
Unfortunately though nothing has ever been done about it and as the old saying goes 'it's been swept under the carpet'.
It has been a while now without a cracked flare on this kit but, recently I have came across cracked flares on split-type a/c (2 other well known manufacturers).
The 1st split had the 3/8" liquid line flare cracked @ indoor cassette and the 2nd split had the 3/4" suction line flare cracked @ condensing unit.Very strange.
So,I am now thinking if there is some sort of link with flare nuts and R407C as the split-type units are also operating on this refrigerant!
I am also now thinking that this job aint what it all cracked up to be :D



05-07-2005, 04:27 AM
Hi Jase,

I have seen many times these cracked nuts on small splits.

I don't have a clue why does it happened, the only thing that I can think of, is the expanding and shrinking of the brass during heating or cooling.

Chemi :)

Andy W
05-07-2005, 07:09 AM
I have had it many times on R22 over the years particular on wall mounts and they are always real difficult to repair after installation. Every single wall mount I install with no exceptions, I cut the flare nuts from the back of the wall mount and solder the pipes instead. It is the expansion and contraction of the materials and as most materials are recycled..........

05-07-2005, 08:37 AM
The use of flares should not only be discouraged but eradicated completely. It can be done.
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05-07-2005, 10:41 AM
Yep, suction flares are the worst; moisture gets under the threads and freezes when in cooling. Expansion then works of the nut and over time......

The use of something like Leak Lok on the threads will stop the ingress of moisture and prolong its life.

The other problem is the installation guy overtightening the joint and cracking the nut on day one. The leak starts after he has left !

05-07-2005, 01:10 PM
The other problem is the installation guy overtightening the joint and cracking the nut on day one. The leak starts after he has left !

That's also my experience Brian. If a flare nut is over tightened, it tends to be over stressed which leads to a fracture. AC manufacturers give guidelines as to the torque that these fittings should be tightened to. The use of a torque wrench is the way to go but most installers just "give 'em a little bit more" just to make sure.

Maybe the installation guys should do a spot of call out and maintenance to see the rewards of their work :D

05-07-2005, 01:33 PM
Yes, agreed Frank. The fact that they recommend (insist??) that R410 flares should be tightened with a torgue spanner may perhaps begin the trend which will, hopefully, reduce the problem.

Also, throwing away the installers set of Stilsons may also help:D

chillin out
05-07-2005, 07:03 PM
Couldn`t agree more install lads get it easy, they just fit brand new parts usually during normal working hours and even if they do overtime its planned well in advance.

The use of flares should not only be discouraged but eradicated completely.

This could only come from somebody other than a service tech. Braizing parts in is a complete pain in the behind. :(

Its not nice having to braize in tevs or driers when its 2am. Especially when you try and have nitro flowing to stop oxodisation.
Pump a pack down, reclaim all left over gas, break vac with nitro, set up nitro to flow, braize in part, vac system, top up gas..... all this while 20 cases are alarming out...no thanks.

piston broke
05-07-2005, 09:25 PM
Cracked Nuts!

Sounds serious. I would go and see a doctor.


08-07-2005, 07:30 PM
yea i have had the same problem on daikin vrv at the royal bank of scotland. it was funny that about all the 8 vrvs had the same problem and only at this site . i think it is faulty batch of flare nuts my self.

cheers dougie.

piston broke
08-07-2005, 07:37 PM
Dougie, I think I think I know the job you speak of. You probably work for the same company as me and Jase.

I think there its a combination of things and the bottom line is that materials, eg flare nuts are not of the same quality they used to be and therefore can't stand stand that extra turn.

I suppose we better ask the chiefs for torque wrenches.


08-07-2005, 08:33 PM
Hi everyone

I was told many years ago that the fractures on flare nuts was being caused by the chemicals within the most usefull leak finding substance --- fairy liquid- and the reaction on the brass of the Fl nut .

On pressure testing of the system, the installer will go around and check the flare joints with watered down fairy liquid but he will never wash down the joints with clean water, years later the flare nut will crack open.

This however just could be a fairy tale.


08-07-2005, 09:15 PM
Either a faulty batch or an exuberant techi who on installation tightened over the torque limits, thus hastening their demise

08-07-2005, 10:56 PM
This however just could be a fairy tale.You could be right BobJob, Fairy Liquid, and other washing liquids, contain salt as a wtaer softening agent and salt, of course, corrodes metals.

That is why the Gas Authority does not allow the use of washing liquids as a leak detector anywhere near a gas meter and it's associated pipework.

piston broke
09-07-2005, 08:56 AM
Very interesting eh Jase. I think the subbies who installed that system may very well use fairy liquid even though we provide them with proper leak detection spray.

I shall try and find out but you know they'll never admit it.


09-07-2005, 07:03 PM
Hi Jase

Are you the same Jase that posted this problem on the IOR forum?

10-07-2005, 11:30 AM
Hi Frank

Yes it is indeed me ;)
Why you ask?


Greg Alexander
10-07-2005, 10:01 PM
Hi Guys,

talking of torque wrenches, does anyone know where i can get a 3/4 head for my refco set or if it is available because the supplier told me if i want 3/4 i have to file down my 5/8 head. Great eh!! The suction nut on the indoor R410a Mitsibishi are 3/4. Or are there other sets available with a 3/4 head.
cheers in advance
Greg :)