Evaporator Coil Metering Devices; Thermostatic Expansion Valve (Txv); Txv Operation; Replacing Txv - Bryant Preferred 549K 04-06 Service And Maintenance Instructions

Table 3 — Cooling Mode (each circuit)
COMPONENT
Reversing Valve
Check Valve A
Check Valve B
Check Valve C
Check Valve D
Table 4 — Heating Mode (each circuit)
COMPONENT
Reversing Valve
Check Valve A
Check Valve B
Check Valve C
Check Valve D
Table 5 — Defrost Mode
COMPONENT
Defrost Thermostat
Outdoor Fan(s)
Reversing Valve
Check Valve A
Check Valve B
Check Valve C
Check Valve D

Evaporator Coil Metering Devices

549K 04-06 units use a TXV-distributer system for evaporator
metering.

THERMOSTATIC EXPANSION VALVE (TXV)

All 549K units have a factory-installed nonadjustable thermo-
static expansion valve (TXV). The TXV is a bi-flow, bleed port
expansion valve with an external equalizer. The TXVs are spe-
cifically designed to operate with Puron
Use only factory-authorized TXVs.

TXV Operation

The TXV is a metering device that is used in air conditioning
and heat pump systems to adjust to the 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 the following:
1. Superheat temperature is sensed by cap tube sensing bulb
on suction tube at outlet of evaporator coil. This tempera-
ture is converted into pressure by refrigerant in the bulb
pushing downward on the diaphragm, which opens the
valve using the push rods.
2. The suction pressure at the outlet of the evaporator coil is
transferred through the external equalizer tube to the
underside of the diaphragm.
3. The pin is spring loaded, which exerts pressure on the
underside of the diaphragm. Therefore, the bulb pressure
works against the spring pressure and evaporator suction
pressure to open the valve. If the load increases, the tem-
perature increases at the bulb, which increases the pressure
on the top side of the diaphragm. This opens the valve and
increases the flow of refrigerant. The increased refrigerant
flow causes the leaving evaporator temperature to
decrease. This lowers the pressure on the diaphragm and
closes the pin. The refrigerant flow is effectively stabilized
to the load demand with negligible change in superheat.

Replacing TXV

1. Recover refrigerant.
2. Remove TXV support clamp using a
STATUS/POSITION
Energized
Closed
Open
Closed
Open
STATUS/POSITION
De-energized
Open
Closed
Open
Closed
STATUS/POSITION
Closed
Off
Energized
Closed
Open
Closed
Open
(R-410A) refrigerant.
®
/ -in. nut driver.
5
l6
12
3. Remove TXV using a wrench and an additional wrench on
connections to prevent damage to tubing.
4. Remove equalizer tube from suction line of coil. Use file
or tubing cutter to cut brazed equalizer line approximately
2 inches above suction tube.
5. Remove bulb from vapor tube inside cabinet.
6. Install the new TXV using a wrench and an additional
wrench on connections to prevent damage to tubing while
attaching TXV to distributor.
7. Attach the equalizer tube to the suction line. If the coil has
a mechanical connection, then use a wrench and an addi-
tional wrench on connections to prevent damage. If the
coil has a brazed connection, use a file or a tubing cutter to
remove the mechanical flare nut from the equalizer line.
Then use a new coupling to braze the equalizer line to the
stub (previous equalizer line) in suction line.
8. Attach TXV bulb in the same location where the original
(in the sensing bulb indent) was when it was removed,
using the supplied bulb clamps. See Fig. 19.
9. Route equalizer tube through suction connection opening
(large hole) in fitting panel and install fitting panel in place.
10. Sweat the inlet of TXV marked "IN" to the liquid line. Avoid
excessive heat which could damage the TXV valve. Use
quenching cloth when applying heat anywhere on TXV.
CLAMP
TXV SENSING
BULB
SENSING BULB INSULATION REMOVED FOR CLARITY
Fig. 19 — TXV Valve and Sensing Bulb Location

Refrigerant System Pressure Access Ports

There are two access ports in the system: on the suction tube near
the compressor and on the discharge tube near the compressor.
These are brass fittings with black plastic caps. The hose connec-
tion fittings are standard / -in. SAE male flare couplings.
1
4
The brass fittings are two-piece high flow valves, with a recep-
tacle base brazed to the tubing and an integral spring-closed
check valve core screwed into the base. See Fig. 20. This check
valve is permanently assembled into this core body and cannot
be serviced separately; replace the entire core body if neces-
sary. Service tools are available from RCD that allow the re-
placement of the check valve core without having to recover
the entire system refrigerant charge. Apply compressor refrig-
erant oil to the check valve core's bottom o-ring. Install the
fitting body with 96 ± 10 in.-lb (10.85 ± 1.1 Nm) of torque; do
not over-tighten.
THERMAL EXPANSION
(TXV) VALVE