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The discharge line pressure drop should not exceed 9 PSI (62 kPa) for R-410A 6 PSI (41 kPa) for R-
407C. Recommended gas velocity for proper oil return is 1,000 FPM (5.1 m/sec). Slope horizontal lines
downward in the direction of the refrigerant flow. The recommended sl
ope is 1/2” (12 mm) for every ten
(10) feet (3 m) of line length. Discharge lines do not require insulation but due to the high temperatures
of the refrigerant inside the line, the pipes may be insulated to protect against burns to individuals near
or around the lines.
Liquid Lines
Liquid line size is determined by pressure drop and velocity. The liquid line pressure drop should not
exceed 9 PSI (62 kPa) for R-410A and 5 PSI (35 kPa) for R-407C. The recommended liquid velocity
should be between 200 and 300 FPM (1 to 1.5 m/sec). To avoid excessive liquid line pressure drop,
the air-cooled condenser should be located above or at the same level as the evaporator. Condenser
installations more than 15 feet (4.6 m) below the evaporator are not recommended. Insulation of liquid
lines is not required but can be useful in preventing excessive subcooling or flashing on long exposed
pipe runs.
Suction Lines
Some applications call for the compressor to be mounted as part of the condenser, more commonly
referred to as a condensing unit. Such cases require field piping of liquid and suction lines. Suction
lines are trapped similarly to discharge lines. Common practice for suction line selection and installation
should be followed. Suction lines should always be insulated.
Recommended Line Sizing
Table 1 Line Size Metric Conversion
Inch OD
mm
Inch OD
mm
3/8
9 mm
1-1/8
29 mm
1/2
12 mm
1-3/8
35 mm
5/8
16 mm
1-5/8
41 mm
3/4
19 mm
2-1/8
54 mm
7/8
22 mm
NOTE:
All line sizes shown in this document are Outside Diameter (OD)
unless otherwise specified.
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