10
SS-APG008H-EN
WARNING
Risk of Explosion with Refrigerant Line!
Failure to follow instructions could cause a refrigerant
line to explode under pressure which could result in
death or serious injury.
Liquid refrigerant trapped between two valves can
become highly pressurized if the ambient temperature
increases. DO NOT add a liquid line solenoid valve in
a cooling-only system that is already equipped with a
check valve.
Moisture-Indicating Sightglass
Be sure to install one moisture-indicating sight glass in the
main liquid line.
Note:
The sole value of the glass is its moisture-indicating
ability. Use the Installation manual charging curves
—not the sightglass—to determine proper charge
levels.
Expansion Valve
The expansion valve is the throttling device that meters the
refrigerant into the evaporator coil. Metering too much
refrigerant floods the compressor; metering too little
elevates the compressor temperature. Choosing the
correct size and type of expansion valve is critical to ensure
that it will correctly meter refrigerant into the evaporator coil
throughout the entire operating envelope of the system.
Correct refrigerant distribution into the coil requires an
expansion valve for each distributor.
For improved modulation, choose expansion valves with
balanced port construction and external equalization.
, identifies the part number of the valve
recommended for TTA/TWA systems. The tonnage of the
valve should represent the tonnage of the portion of coil
that the TXV/ distributor will feed.
Some expansion valve models have built-in check valves
for heat pump operation and do not require additional
external check valves for reverse flow operation. TXVs
containing a check valve are identified in
.
The TWE air handler ships with a factory installed
expansion device and heat pump check valve. If an
alternate device is required, these factory shipped
components must be removed.
The Microchannel condenser cooling-only units do not
require a bleed TXV valve as required on some other
product types. TXV for TTA microchannel units can also be
selected from
.
Check Valves
WARNING
Risk of Explosion with Refrigerant Line!
Failure to follow instructions could cause a refrigerant
line to explode under pressure which could result in
death or serious injury.
Liquid refrigerant trapped between two valves can
become highly pressurized if the ambient temperature
increases. DO NOT add a liquid line solenoid valve in
a cooling-only system that is already equipped with a
check valve.
TWA: Due to the reverse cycle of the TWA heat pump, a
check valve is required to bypass refrigerant around the
TXV while the unit is in heating mode. If the air handler is a
TWE, it includes both the TXV and check valve.
TTA: Because of the limited holding capacity of the
microchannel heat exchanger, if more than 50 ft of liquid
line is above a TTA unit, a check valve should be installed
in the liquid line at the TTA unit to prevent backflow during
the off condition. The check valve should be one size larger
than the liquid line to reduce pressure drop and should be
located at the TTA unit. A solenoid valve should never be
used in the liquid line when using this check valve.
Gas Line
Line Sizing
Proper line sizing is required to guarantee that the oil
returns to the compressor throughout the system’s
operating envelope. At the same time, the line must be
sized so that the pressure drop does not excessively affect
capacity or efficiency. To accomplish both objectives, it may
be necessary to use two different line diameters: one for
the horizontal run and for the vertical drops, and another for
the vertical lifts (risers).
Note:
Preselected suction-line diameters shown in the
Component Selection tables found in
are independent of total line length for properly
charged 6 – 25 ton TTA/TWA in normal air-
conditioning applications.
Routing
Route the line as straight (horizontally and vertically) as
possible. Avoid unnecessary changes of direction. To
prevent residual or condensed refrigerant from “free-
flowing” toward the compressor, install the gas line so that
it slopes by ¼ to 1 inch per 10 feet of run (1 cm per 3 m)
toward the indoor coil.
Do not install riser traps. With field-supplied air-handler
coils, what appears to be a riser trap is located at the coil
outlet; see
for an example. This piping
arrangement, which isn’t a riser trap, is the result of two
requirements:
•
Drain the coil to the common low point.
