Thermostatic-Expansion Valve (Bi-Flow Txv); Coil Removal; Liquid-Line Strainer (Heat Pumps Only) - Bryant R-22 Application Manual And Service Manual

TABLE 20—TXV SUPERHEAT SETTING AT OUTLET OF EVAPORATOR COIL
INSTALLATION
Field Accessory
Field Accessory
Field Accessory/Factory-Installed
Factory-Installed
Factory-Shipped/Field-Installed
TO
FROM
ACCUMULATOR
OUTDOOR
COIL
TP-4 TP-3
INSULATE FOR
ACCURATE
READING
FROM COMPRESSOR
DISCHARGE LINE
THERMOMETER
Fig. 48—Reversing Valve (Heating Mode, Solenoid De-
Energized)
Hard Shutoff (HSO)—Has no bleed port and allows no bleed-
through after system shutdown. No pressure equalization occurs.
Because of unequalized system pressures, a start capacitor and
relay must be installed on single-phase reciprocating compressors
to start the compressor.
See Table 20 for TXV superheat settings. These settings are
factory set and are not field adjustable. Table 17 settings are for
Bryant-approved accessories and factory-installed TXVs only.
VIII. THERMOSTATIC-EXPANSION VALVE (BI-FLOW
TXV)
The standard TXV is a metering device that is used in condensing
and heat pump systems to adjust to changing load conditions by
maintaining a preset superheat temperature at the outlet of the
evaporator coil. The volume of refrigerant metered through the
valve seat is dependent upon:
1. Superheat temperature sensed by cap-tube sensing bulb on
suction tube at outlet of evaporator coil. As long as this bulb
and cap tube contains some liquid refrigerant, this tempera-
ture is converted into suction pressure pushing downward
on the diaphragm, which tends to open the valve via the
pushrods.
2. The suction pressure at the outlet of the evaporator coil is
transferred via the external equalizer tube to the underside
of the diaphragm.
3. The needle valve on the pin Bryant is spring-loaded, which
also exerts pressure on the underside of the diaphragm via
the pushrods, which tends to close the valve. Therefore,
bulb pressure equals evaporator pressure (at outlet of coil)
plus spring pressure. If the load increases, the temperature
increases at the bulb, which increases the pressure on the
topside of the diaphragm, which pushes the pin Bryant
away from the seat, opening the valve and increasing the
flow of refrigerant. The increased refrigerant flow causes
TXV TYPE
RPB/HSO
RPB/HSO
HSO
HSO
HSO
TO INDOOR COIL
VIA SERVICE VALVE
ON OUTDOOR COIL
INSULATE
FOR
TP-2
ACCURATE
READING
TP-1
ELECTRONIC
A88341
PRODUCT USAGE
Air Conditioner Indoor Unit
Heat Pump Indoor Unit
Indoor Fan Coil Unit
2-Speed Heat Pump Outdoor Unit
2-Speed Indoor Unit
increased leaving evaporator pressure, which is transferred
via the equalizer tube to the underside of the diaphragm.
This tends to cause the pin-Bryant spring pressure to close
the valve. The refrigerant flow is effectively stabilized to
the load demand with negligible change in superheat. The
bi-flow TXV is used on split-system heat pumps. In the
cooling mode, the TXV operates the same as the standard
TXV previously explained. (See Fig. 49.)
However, when the system is switched to the heating mode
of operation, the refrigerant flow is reversed. The bi-flow
TXV has an additional internal-check valve and external
tubing. (See Fig. 50.) These additions allow the refrigerant
to bypass the TXV when refrigerant flow is reversed with
only a 1- to 2-psig pressure drop through the device. When
the heat pump switches to the defrost mode, the refrigerant
flows through a completely open (unthrottled) TXV, and
the bulb senses the residual heat of the outlet tube of the coil
that had been operating in the heating mode (about 85°F
and 155 psig). This temporary, unthrottled valve decreases
the indoor-pressure drop, which in turn increases the
refrigerant-flow rate, decreases overall defrost time, and
enhances defrost efficiency.
IX. COIL REMOVAL
Coils on this family of units are easy to remove, if required for
compressor removal or replacement coil.
CAUTION: Wear safety glasses and gloves when han-
dling refrigerants.
To remove or replace coil:
1. Shut off all power to unit.
2. Remove and recover refrigerant from system through ser-
vice valves.
3. Remove top cover. (See Remove Top Cover section.)
4. Remove screws in base pan to coil grille.
5. Remove coil grille from unit.
6. Remove screws on corner-post (Reliant) service-valve
panel (Cube unit) holding coil-tube sheet.
CAUTION: Cut tubes to reduce the possibility of fire
and personal injury.
7. Use midget-tubing cutter to cut liquid and vapor lines at
both sides of coil. Cut in convenient location for easy
reassembly with copper-slip couplings.
8. Lift coil vertically from basepan. Place aside carefully.
9. Reverse procedure to reinstall coil.
X. LIQUID-LINE STRAINER (HEAT PUMPS ONLY)
The liquid-line strainer is upstream of the heating piston. The
strainer catches debris in the liquid line during heating mode. If it
becomes plugged, system operation and pressure become abnor-
mal, and the compressor may become hot and cycle off on the
overloads or pressure relief.
—41—
SUPERHEAT SETTING
10°
6°
6°
4°
4°