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NOZZLE
RETAINER
RING
SIMPLIFIED NOZZLE
REMOVAL
G
5
NO. 6-32 THREADED
PULLER HOLES
Fig. 106 — Nozzle Change-Out
Filter Drier
A filter drier should be installed before the TXV to ensure satis-
factory valve operation.
TXV (Thermostatic Expansion Valve)
TXV LOCATION
Thermostatic expansion valves may be mounted in any position,
but they should be installed as close to the evaporator as possible.
If a refrigerant distributor is used with the TXV, best performance
is obtained if the distributor is mounted directly to the valve outlet.
If the distributor cannot be mounted directly to the valve outlet,
the distance between the valve outlet and distributor should not
exceed 24 in. or refrigerant distribution problems may occur. Also,
the tube connecting the valve outlet and distributor can be sized
smaller to maintain refrigerant velocity and better distribution. El-
bows located between the expansion valve and distributor will
hinder proper distribution and are, therefore, not recommended.
IMPORTANT: There are no liquid line penetrations through the
casings from the factory. Best distribution is usually obtained if
the expansion valve feeds vertically up or down into the distrib-
utor. Assemble the refrigerant piping and specialties inside the
cabinet to determine the hole location prior to using a hole saw
to penetrate the cabinet.
While not always convenient or possible, valve Types BI, F, FB,
and O are easier to service if mounted in a vertical and upright po-
sition. If mounted in a horizontal position, the internal parts must
be carefully reassembled to prevent damage. Some consideration
should also be taken in mounting larger sized expansion valves.
They must be adequately supported since system vibration and the
weight of the valve can cause valve connections to fracture.
SOLDER TECHNIQUES
It is not necessary to disassemble solder type valves when solder-
ing to the connecting lines. Any of the commonly used types of
solders, e.g., 95-5, Sil-Fos, Easy-Flo, Phos-Copper, Stay Brite 8 or
equivalents, may be used for copper-to-copper connections. When
soldering a brass refrigerant distributor to the valve, appropriate
solders for these connections, such as 95-5, Easy-Flo, Stay Brite 8
or equivalents must be used. Regardless of the solder used, it is
important to direct the flame away from the valve body and avoid
BODY
TUBING
a39-2041
THREADED
PULLER RODS
excessive heat on the diaphragm. See Fig. 107 for details. As an
extra precaution, a wet cloth should be wrapped around the body
and element during the soldering operation.
NOTE: This precaution will prevent overheating the valve body
which could damage the superheat spring and result in flood-back
problems. In addition, the Type O, EBF/SBF, and EBS valves con-
tain synthetic parts which can be damaged due to overheating, re-
sulting in poor valve performance.
a39-3970
Fig. 107 — Solder Technique
TXV BULB LOCATION AND INSTALLATION
The location and installation of the bulb is extremely important to
the proper performance of the system. Therefore, care should be
taken with its final location. Laboratory testing has shown that bet-
ter sensing can be achieved with the sensing bulb mounted on a
vertical riser. However, with proper piping practices, horizontal
mounting will also provide adequate sensing. When the horizontal
mounting location is used, the suction line must drop below the
coil suction outlet, as shown in Fig. 108. This line is pitched
slightly downward, and when a vertical riser follows, a short trap
is placed immediately ahead of the vertical line. See Fig. 108. The
trap will collect any liquid refrigerant or oil passing through the
suction line and prevent it from influencing the bulb temperature.
Steps for using a vertical riser as shown in Fig. 108 are:
1.
A minimum of two 90-degree elbows must be installed
upstream of the expansion bulb location. A distance of 8 pipe
diameters between the elbows is desirable.
2.
The thermal bulb must be strapped to a vertical riser follow-
ing the second elbow of item 1. This riser must be at least 15
pipe diameters high and the bulb should be fastened 10 pipe
diameters above the preceding elbow.
3.
Size the suction line from near the evaporator through the 15
pipe diameter long riser for high velocity. It is recommended
that the suction pipe sizing charts in the Refrigerant Refer-
ence Manual be used, entering at corrected design tons (each
evaporator split) and 80 feet equivalent length (for 2°F loss).
The chart point usually falls between 2 sizes; choose the
smaller size pipe. Since the selection of suction piping recom-
mended for high velocity is approximately 20 feet equivalent
length, this sizing method will result in about 0.5°F friction
loss for that section. If the commonly selected 2°F loss is
allowed for the entire suction line, this leaves 1.5°F for the
balance of the suction line and it should be sized on that basis.
Usually, this high velocity sizing will be adequate for oil
return up the 15 diameter long riser, though it should be
checked.
The purpose of these recommendations is to achieve good mixing
of the refrigerant leaving the evaporator suction header for proper
sensing by the TXV bulb. Tests have confirmed that this, in addi-
tion to the vertical riser bulb location, results in significantly better
superheat control over a broader load range.
Figures provided in the Carrier Refrigerant Reference Manual il-
lustrate these recommendations for various coil splits and com-
pressor configurations.
139
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