First off we need to clarify that very few unitary manufacturers use flares anymore. You will most often find flares on ductless and VRF / VRV systems and in refrigeration. A flare uses a flared female cone formed into tubing (usually copper) that is pressed onto a male cone (usually brass) by a threaded flare nut. A flare shouldn’t be confused with a chatleff fitting that uses a threaded nut and seals with teflon or nylon seal.
This is not a full lesson on how to make a flare, this will give you some best practices to make a flare that doesn’t leak.
- Use proper depth, the old school method is to bring the copper up a dimes width above the block but modern flaring blocks usually have built in gauges that work well.
- Don’t trust factory flares. In many cases factory line-set flares are made poorly, often it’s better to just cut them off and start over
- Ream the copper before flaring to remove the burr but don’t OVEREAM and thin out the copper edge.
- Use a good, modern, concentric flaring tool with a 45-degree cone and block. This is a great one
- When making the flare use a bit of refrigerant oil, or even a better a bit of Nylog. You only need a drop or two, one drop on the flare while making it to prevent binding and create a smoother flare surface with a bit on the back of the flare as well to allow the nut to slide easily. I also like one small drop on the threads and spread to the mating surfaces. Some manufacturers disagree with this due to the effect it has on torque specs so always follow their recommendations when in doubt.
- Use a flare wrench instead of an adjustable wrench and tighten with a torque wrench. I understand that very few techs do this… but it is a great practice if you want to get it right the first time with no leaks and no damage. This can be done easily be done with a set of SAE crowsfoot flare nut wrenches and a 3/8″ torque wrench. As always use manufacturers torque specs if available. If not you may use the chart below. Make sure to keep the crowsfoot at 90 degrees to the wrench (perpendicular) and place your hand on the end grip of the wrench. If you have lubricant on the threads stay on the low side of the torque rating.
Some things NOT to do that I’ve seen –
- Don’t use leak lock or teflon tape on flares
- Don’t Over Tighten flares to try and get them to stop leaking. If they are properly torqued and still leak they are made wrong
- Don’t use too much oil or nylog, a drop or two will do
- Don’t try and jam a teflon seal from a chatleff on a flare
Using these practices we have VERY FEW leaks on flare fittings.
Some other things to note –
There is a company called Spin that uses a flaring tool that goes on a drill. Their tool actually heats and anneals the copper. They claim they don’t need to get the flare to 45 degrees because the annealing makes the copper soft enough that the nut itself with finish the flare. We have used it a few times with good results.
There are now companies that make nylon / teflon (I’m actually not sure what they are made of) gasket inserts that go into a flare. Some techs swear by them, I really don’t see the necessity but I don’t have any experience with them.