FCM4, FEV, FEM4, FJM, FMA4, FSA4, FSM4, FSU4, FVM4, FXM4, REM4, WAH, WAM, WAP, WAX, WBHL: Service and Maintenance Instructions
Manufacturer reserves the right to change, at any time, specifications and designs without notice and without obligations.
24
A86006
Fig. 20 – Motor, Inlet Ring, and Blower Wheel Assembly
Refrigerant Flow-Control Devices
Thermostatic Expansion Valves (TXV)
NOTE: 2023 models (FJM) use a mechanical TXV. Refer to the TXV
Installation Instructions. Torque the equalizer fitting to 10–20 ft-lb; do
not exceed 20 ft-lb.
The FCM4X, FEM4X, FEV, FJM, FSA4X, FVM4, FXM4X, REM4X,
WAHM, WAHT, WAHL, WAXM, WAXT, WAXL, and WBHL Fan
Coils are factory equipped with a hard shutoff (HSO) TXV. The hard
shutoff TXV has no bleed port and allows no bleed-through after system
is shutdown.
The TXV is a bi-flow metering device that is used in condensing and
heat pump systems to adjust to changing load conditions by maintaining
a preset superheat temperature at outlet of evaporator coil. The volume
of refrigerant metered through valve seat is dependent upon the
following:
1. Superheat temperature sensed by sensing bulb on suction tube at
outlet of evaporator coil. As long as this bulb contains some liquid
refrigerant, this temperature is converted into pressure pushing
downward on the diaphragm, which opens the valve via push rods.
2. The suction pressure at outlet of evaporator coil is transferred via
the external equalizer tube to underside of diaphragm.
The bi-flow TXV is used on split system heat pumps. In cooling mode,
TXV operates the same as a standard TXV previously explained.
However, when system is switched to heating mode of operation,
refrigerant flow is reversed.
The bi-flow TXV has an additional internal check valve and tubing.
These additions allow refrigerant to bypass TXV when refrigerant flow
is reversed with only a 1-psig to 2-psig pressure drop through device.
When heat pump switches to defrost mode, refrigerant flows through a
completely open (not throttled) TXV. The bulb senses the residual heat
of outlet tube of coil that had been operating in heating mode (about
85_F and 155 psig). This temporary, not-throttled valve decreases indoor
pressure drop, which in turn increases refrigerant flow rate, decreases
overall defrost time, and enhances defrost efficiency.
Problems Affecting TXV
Low Suction Pressure
1. Restriction in TXV
2. Low refrigerant charge
3. Low indoor load
4. Low evaporator airflow
High Suction Pressure
1. Overcharging
2. Sensing bulb not secure to vapor tube
3. High indoor load
4. Large evaporator face area
NOTE: When installing or removing TXV, wrap TXV with a wet cloth.
When reattaching TXV, make sure sensing bulb is in good thermal
contact with suction tube.
5. The needle valve on pin carrier is spring-loaded, which also exerts
pressure on underside of diaphragm via push rods, which closes
valve. Therefore, bulb pressure equals evaporator pressure at outlet
of coil plus spring pressure. If load increases, temperature increases
at bulb, which increases pressure on topside of diaphragm, which
pushes pin carrier away from seal, opening valve and increasing
flow of refrigerant. The increased refrigerant flow causes increased
leaving evaporator pressure which is transferred via the equalizer
tube to underside of diaphragm, with which the pin carrier spring
pressure closes valve. The refrigerant flow is effectively stabilized
to load demand with negligible change in superheat.
Aluminum Coil Unit TXV’s
The distributor used on the all-aluminum coils is also made of
aluminum. The TXV connection to the distributor is accomplished with
a 3/4-inch Chatleff nut (Fig. 21). The threads are coated with Loctite
Heavy Duty Anti-Seize which is a graphite/calcium fluoride
formulation, for applications that is free from copper, lead and sulfur.
This product is typically used in applications with an operating range of
-20°F to +2400°F. When replacing a TXV it is recommended to reapply
with the same thread sealer.
Extra care should be taken during brazing of copper equalizer on the
aluminum coils to prevent the braze material from splattering on the
aluminum. Also, route the copper equalizer so that it does not touch the
aluminum components.
GROMMET
BLOWER
WHEEL
INLET
RING
MOTOR
1
1
⁄8≤
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