ASHRAE Journal - January 2021 - 38

TECHNICAL FEATURE

* An " eccentric " cone that rolls around the interior of
the tubing, forming it into shape; and
* A clutch that disengages the cone when the flare is
complete.
Battery-powered flaring tools share these features, but
spin the cone much faster, annealing the copper and
making it less brittle.
Prior to assembly, check that the flare is symmetrical
and that contact surfaces are clean, shiny, and free of
scratches. Apply a thin coat of refrigeration oil or an
approved assembly lubricant to the contact surface to
improve the seal, as well as to the back of the flare nut to
keep it from binding. Align the cones and hand-tighten
the flare nut.
Once the flare is assembled, tighten it to spec using
a torque wrench (Figure 2). If the assembly is too loose,
the surfaces will not form a good seal; if it is too tight,
the flare will crack or split. Torque specs are found in
manufacturers' instructions and range from around
13 ft·lbf (17.6 N·m) for ¼ in. (6.4 mm) tubing to around
56 ft·lbf (75.9 N·m) for 5/8 in. (15.9 mm) tubing. Torque
wrenches, available in digital and analog models, prevent the installer from over-torquing smaller flares and
under-torquing larger ones.
Always use flare nuts supplied with the equipment.
Manufacturers' torque specs are for OEM flare nuts,
which tend to be longer (with more threads) and of better quality than aftermarket ones. If subsequent testing
reveals a leak at any flare connection, do not attempt
to tighten it further; cut off the defective flare and start
again.
While inverter-driven ASHPs usually use flare connections, other approaches are gaining traction. Brazing,
used widely in other areas of HVAC&R, involves soldering joints with a phosphorus/silver/copper alloy. Done
correctly, brazing provides a reliable, leak-free joint.
Disadvantages include the work of toting extra equipment (brazing tanks and torches), the need to flow nitrogen through the tubing while brazing to prevent formation of copper oxide scale, and safety concerns around
open flames. Because of its durability, brazing is a good
choice for difficult-to-access connections-for example,
those enclosed in walls or high off the ground. Crimped
and push-fit refrigerant fittings are also becoming
widely available. We are exploring these technologies to
determine whether they meet our criteria for reliability
and cost-effectiveness.
38

ASHRAE JOURNAL

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JAN UARY 2021

Other decisions made during design and installation
can prevent refrigerant loss. Use continuous line sets
wherever possible to reduce potential leakage sites.
Allow for pipe expansion, and properly support and
protect line sets both inside and outside the structure.
Avoid enclosing line sets in wall cavities, where they cannot be inspected and where they may be inadvertently
punctured.
Also, take steps to protect refrigerant lines and coils
from corrosive chemicals. Salt-spray damage (in coastal
settings and from road salt) can be mitigated by physical
barriers, periodic rinsing of the outdoor equipment with
fresh water, and protective coatings. Corrosion from dog
urine can be avoided by fencing or elevating the outdoor
unit.
Refrigerant loss can also occur in cold climates
when built-up ice crushes outdoor coils. This can be
avoided by providing good drainage below the unit and
ensuring that a base-pan heater is installed. In snowy
areas, moisture load on outdoor units can be reduced
by avoiding driplines or installing snow-shields or
awnings.
Another source of refrigerant loss is intentional inhalation ( " huffing " ) of refrigerants, mainly by teenagers. Some
jurisdictions have adopted provisions in the International
Mechanical Code and International Residential Code that
require locking caps on charging ports.

Testing

Installed refrigerant piping must be tested for leaks
prior to charging the system. The standing pressure test
involves filling the system with nitrogen. Once the system is pressurized, isolated and allowed to stabilize, it
must hold steady for a specified period. Pressurization
should be done gradually so that catastrophic leaks are
caught with minimal waste. The target pressure, specified by the manufacturer, is typically 500 psig to 550 psig
(3447 kPa to 3792 kPa).
The standing pressure test alone will reveal large leaks,
but its sensitivity is limited by gauge precision and the
duration of the test. Analog pressure gauges can be read
to about the nearest psi; digital gauges typically have a
resolution of 0.1 psi (689 Pa). Under perfectly stable outdoor air temperature conditions, any measurable drop
in pressure over the test period would represent a leak
that would lead to significant refrigerant loss over the
15- to 20-year life of the system.

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ASHRAE Journal - January 2021

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