Evaporator Coil; Evaporator Coil Metering Devices; Thermostatic Expansion Valve (Txv); Txv Operation - Carrier 50FC 08-16 Series Service And Maintenance Instructions

5. Thoroughly apply Totaline environmentally balanced coil
cleaner solution to all coil surfaces including finned area,
tube sheets and coil headers.
6. Hold garden sprayer nozzle close to finned areas and apply
cleaner with a vertical, up-and-down motion. Avoid spraying
in horizontal pattern to minimize potential for fin damage.
7. Ensure cleaner thoroughly penetrates deep into finned
areas. Interior and exterior finned areas must be thor-
oughly cleaned. Finned surfaces should remain wet with
cleaning solution for 10 minutes. Ensure surfaces are not
allowed to dry before rinsing. Reapply cleaner as needed
to ensure 10-minute saturation is achieved.
8. Thoroughly rinse all surfaces with low velocity clean
water using downward rinsing motion of water spray noz-
zle. Protect fins from damage from the spray nozzle.

Evaporator Coil

Cleaning the Evaporator Coil
1. Turn unit power off. Install lockout tag. Remove evapora-
tor coil access panel.
2. If economizer or two-position damper is installed, remove
economizer by disconnecting Molex
mounting screws.
3. Slide filters out of unit.
4. Clean coil using a commercial coil cleaner or dishwasher
detergent in a pressurized spray canister. Wash both sides
of coil and flush with clean water. For best results, back-
flush toward return-air section to remove foreign material.
Flush condensate pan after completion.
5. Reinstall economizer and filters.
6. Reconnect wiring.
7. Replace access panels.

Evaporator Coil Metering Devices

50FC-08-16 units with or without the Humidi-MiZer option use a
TXV-distributer system.

THERMOSTATIC EXPANSION VALVE (TXV)

All 50FC-08-16 units equipped with the Humidi-MiZer option
include TXV control. The TXV is a bi-flow, bleed port expansion
valve with an external equalizer. The TXVs are specifically
designed to operate with Puron
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 under-
side of the diaphragm.
1. Third-party trademarks and logos are the property of their respective
owners.
®1 plug and removing
® refrigerant. Use only factory-
3. The pin is spring loaded, which exerts pressure on the under-
side 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 temperature
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 negligi-
ble change in superheat.

Replacing TXV

1. Recover refrigerant.
2. Remove TXV support clamp using a 5/l6-in. nut driver.
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 additional
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. 23 on page 16.
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.

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 1/4-in. SAE male flare couplings.
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. 24. 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 fit-
ting body with 96 ± 10 in.-lb (10.85 ± 1.1 Nm) of torque; do
not over-tighten.
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