Figure 6-44.The defrost cycle of an ice cube machine.
shutdown periods. If siphoning starts, the liquid
refrigerant flashes into a gas at the top of the loop,
breaking the continuity of the liquid volume and
stopping the siphoning action. Where the cooling
coils and compressors are on the same level, both the
suction and liquid lines should be run to the overhead
and then down to the condensing unit, pitching the
suction line toward the compressor to ease oil return.
On close-coupled installations, running both lines up
to the overhead helps to eliminate vibration strains as
well as provide the necessary trap at the cooling coil.
Prepare pipe and fittings with care, particularly
when cutting copper tubing or pipe to prevent filings or
cuttings from entering the pipe. The small particles of
copper should be completely removed since the finely
divided copper may pass through the suction strainer.
The tube should be cut square, and all burrs and dents
should be removed to prevent internal restrictions and
to permit proper fit with the companion fittings. If a
hacksaw is used to cut, a fine-toothed blade should be
used, preferably 32 teeth per inch. The use of a
hacksaw should be avoided whenever possible. When
making silver-solder joints, brighten up the ends of the
tubing or pipe with a wire brush or crocus cloth to make
a good bond. Do not use sandpaper, emery cloth, or
steel wool for this cleansing, as this material may enter
the system and cause trouble.
Acid should never be used for soldering, nor
should flux be used if its residue forms an acid. Use
flux sparingly so no residue will enter inside the
system and eventually be washed back to the
compressor crankcase. If tubing and fittings are
improperly fitted because of distortion, too much flux,
solder, and brazing material may enter the system.
The temperature required to solder or braze pipe
joints causes oxidation within the tubing. The
oxidation eventually will be removed by the
refrigerant flow after the system is in operation. The
oxide breaks up into a fine powder to contaminate the
lubricant in the compressor and to plug strainers and
driers. To eliminate this possibility, provide a neutral
atmosphere within the tube being soldered or brazed.
Use gas-bled nitrogen through the tubing during
soldering or brazing and for a sufficient time after the