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I have been asked, “Can we braze mini-split systems instead of flaring them?”. The answer, technically, is yes. The only question is in a warranty situation, will the manufacturer accept an indoor unit with the flares cut off? In most cases, they should accept them and the manufacturer reps that I have spoken with have said that it is not a problem. However, technicians should verify this themselves with the manufacturer of the particular equipment that they install.
Of course, when we braze copper line set, we make sure to flow nitrogen or another inert gas through the tubes so that oxidation does not occur inside the line set. The technician will still need to flare the connections to the outdoor unit since there are no stubs to braze, only service valves with flare connections. There is usually only one service port at the outdoor unit, and it is on the vapor service valve. This is where the nitrogen will be introduced. Make sure the small, liquid line is not connected to the flare connection on the liquid service valve. The nitrogen will exit out of this small, liquid line tube.
Step by Step Process of Brazing Mini-Split Tubing:
1. The technician will begin by flaring the large suction line tube and connecting this to the outdoor unit. The small, line set tube should not be connected at this point but will remain open on the end. (The small line set tube would be referred to as the low pressure liquid tube since the active metering device is usually in the outdoor unit of a mini split system. This means that during cooling mode, the metering device will lower the pressure of the refrigerant before it enters the small line set tube.)
2. The flare connectors will need to be cut off of the indoor unit copper stubs and the copper tubes must be reamed in the downward position so that any small pieces of copper will fall out of the tube.
3. The copper stubs from the indoor unit should be swaged and the large and small line set tubes should be run into place and inserted into the swages.
4. Next, a flow regulator must be connected onto a nitrogen tank and set to flow at 2-3 CFH (cubic feet per hour). The nitrogen hose will then be connected to the outdoor unit vapor service port. The nitrogen will enter the vapor service port, flow through the large vapor line, through the evaporator coil, and out of the small line set tube near the small low pressure liquid service valve. The nitrogen will not pressurize the tubing but will push any oxygen out of the tubing during the brazing process. This will also help to dehydrate the lines prior to vacuuming.
5. The technician will then braze the swage joints using a small brazing tip and 15% silver brazing rod. The swage joints will either be behind the indoor head unit, inside the building (while the head unit is tilted upward to gain access to the underside of the unit) or outside the building if the stubs penetrate directly through the outside wall. Make sure to use a heat shield when brazing inside the building or outside near the siding.
6. The nitrogen will then be disconnected, and the small, low pressure liquid line will be flared and connected to the outdoor unit flare connection. Make sure to tighten all flare connections to the specified foot/lb torque value. Usually this is 12 ft/lb for ¼” OD copper tube and 27 ft/lb for 3/8” OD copper tube, but always follow manufacturers instructions to avoid future leaks or problems at the connections.
7. The system will then be ready for a pressure test to check for leaks.
It’s okay to use flares as connections as long as you are sure they won’t leak. Below is a video on 10 reasons why flares may leak as well as ways to make sure that they won’t.
Let me know your experience if you had to warranty an indoor mini-split head unit with cut off flares. I would love to know if anyone is having any trouble with a warranty based on the cut off flares and with which manufacturer. You can comment below or email me at info@acservicetech.com, thanks!
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Published: 9/12/2019
Author: Craig Migliaccio
About the Author:Craig is the owner of AC Service Tech LLC and the Author of the book “Refrigerant Charging and Service Procedures for Air Conditioning”. Craig is a licensed Teacher of HVACR, Sheet Metal, and Building Maintenance in the State of New Jersey of the USA. He is also an HVACR Contracting Business owner of 15 years and holds an NJ HVACR Master License. Craig creates educational HVACR articles and videos which are posted at https://www.acservicetech.com & https://www.youtube.com/acservicetechchannel
I caught my Mitsubishi Diamond Certified installer brazing with only a nitrogen purge AFTER the deed, not with low pressure flow during. He claims its OK because the after the fact purge will clean the contamination all out anyway. I disagree. There will be some oxidized surface left that could still cause long term contamination. Why leave it in there? While even braze on a minisplit that is going to get flared fitted on both sides anyways? Yellow Jacket makes a great tubing bender to keep it all one piece. The reason I am studying HVAC as a general contractor is that I am tired of seeing deficient practices in this trade. It is inexcusable given the high prices being…
Great article. Very informative, precise and to the point. However, I have seen a video on YouTube in which a JAPANESE Licensed technician is cutting flares on the internal unit of the mini split system and "soldering" it. The video is in Japanese.
Instead of Oxy-Acetylene, he probably used Map gas to Solder it. This is probably the reason he didn't run Nitrogen in the system. He also mentioned that since the mini split runs on low pressure, it's ok to use Map Gas and solder it instead. Don't know if it would void any warranties or is not allowed to be done here in the US.