Carrier 38HQ 18-24 Installation, Start-Up And Service Instructions Manual page 23

vapor-line size from Table 2. Subtract the
nominal percentage loss from outdoor-unit
presale-literature Detailed Cooling Capacities
data for the given indoor/outdoor combination.
Reference all notes of Table 2.
NOTE: When specifying
insulation, be aware of the following standard
practice:
All standard accessory-tubing kits are supplied
with 3/8-in. insulation on vapor line.
For minimal capacity loss in long-line
application, 1/2-in. insulation should be
specified.
For reference only, the close cell insulation
material specified for accessory tubing kits is a
compound of vinyl, neoprene, or nitrile blends
of these polymers. Performance requirements
include thermal range of 0° F to 200°F (-17.8°
C to 93° C) and a maximum thermal
conductivity of 0.28.
NOTE: Special consideration must be given to
isolating interconnecting tubing from building
structure. Isolate tubing so that vibration or
noise is not transmitted into structure.
Step 3—Metering Device Sizing
The metering device for a long-line application
must be flexible enough to compensate for
frictional losses due to long refrigerant lines
and installed system design (indoor coil above
or below outdoor unit.) The piston or TXV
provides such flexibility.
The piston should be changed for both indoor
coil and outdoor heat pump unit, depending on
system configuration and line length. Tables 4
and 5 provide necessary changes for a given
application.
Use Tables 4 and 5 when selecting correct
piston size. Outdoor unit presale literature
must be consulted to determine metering
devices specified for standard applications.
After determining standard application piston
size(s), refer to Tables 4 and 5 as they relate to
system design (outdoor unit above or below
indoor unit) per equivalent length of tubing.
NOTE: If total equivalent horizontal length is
100 ft or longer, both indoor and outdoor
pistons must be increased 1 full piston size, in
addition to changes required by Tables 4 and 5.
After finding appropriate change in piston
size, add or subtract the change from original
piston number. If piston size is decreased,
round new piston number down to nearest
common piston number found in Table 6. If
piston size is increased, round new piston
number up to nearest common piston number
found in Table 6.
EXAMPLE:
An 042 size heat pump is 75 ft above an 042 size
fan coil. The 042 size heat-pump presale literature
specifies a size 80 indoor piston and size 63 outdoor
piston. To establish correct indoor piston size for a
75 ft vertical separation, refer to Table 4. For a 75 ft
vapor-line
equivalent line length, the piston change is -5.
Therefore subtract 5 from the original indoor piston
size of 80: 80 – 5 = 75
Table 6 provides common piston sizes. In this
instance, 75 is not listed, therefore round DOWN to
next piston size, which would be 74. To establish
correct outdoor piston size for a 75 ft vertical
separation, refer to Table 5. For a 75 ft equivalent
line length, the piston change is +4. Therefore add 4
to the original outdoor piston size of 63: 63 + 4 = 67
Since 67 is listed in Table 6, that is the piston which
should be used. If a 67 size piston were not listed, it
would be necessary to round UP to next piston size.
Step
Tubing Configuration
There are 2 types of liquid-line solenoids: 1 for
single-flow applications and the other for bi-
flow applications. The purpose of having 2
solenoids is to minimize the valve internal-
pressure drop in accordance with refrigerant
flow direction and liquid migration to the
compressor. The bi-flow solenoid is designed
to have minimal refrigerant-pressure drop in
either flow direction, which makes it suitable
for heat pump usage. Refer to Table 7 for
liquid-line solenoid kit part numbers.
NOTE: When installing a liquid-line solenoid,
the system may require a minimum 60-va low-
voltage transformer.
Each type of solenoid has an indicator flow
arrow stamped on the valve body. When
solenoid is closed (not energized) and pressure
is applied in direction of flow arrow, complete
shutoff occurs. If pressure is applied against
direction of flow arrow, leakage through valve
occurs. When determining proper installation
of valve within liquid line, 2 considerations
must be made:
1. Direction of flow arrow
2. Where solenoid is installed in system.
TXVs can only be substituted for liquid-line
solenoids in singleflow air conditioning
systems. Bi-flow TXVs allow liquid migration
to coldest point during off cycles, which could
allow liquid into compressor. Fig. 2 through 5
detail proper installation of liquid-line solenoid
and provide applications where TXVs may be
substituted. Reference all notes of the
appropriate figures.
4—Liquid-Line Solenoid And
17