Evaporator Coil Metering Devices - Carrier 48TC 04 Series Service And Maintenance Instructions

2. If economizer or two- - position damper is installed,
remove economizer by disconnecting Molex plug
and removing mounting screws.
3. Slide filters out of unit.
4. Clean coil using a commercial coil cleaner or dish-
washer detergent in a pressurized garden sprayer.
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

Three different evaporator coil metering systems are used
on 48TC sizes 04- - 16. All units without Humidimizer
option use the Acutrol system for evaporator metering. On
sizes 04- - 14 with Humidimizer option, the Acutrol system
is used for normal cooling and a series combination of
TXV- - Acutrol is used in Humidimizer modes. On size 16
with Humidimizer option, the Acutrol system is replaced
by a TXV- - distributor system; TXV metering is used in all
modes. See Fig. 18.
Unit Size Humidimizer
04--- 14
04--- 14
16
16
Check this unit's informative data plate for Position 6
value, then compare this value to Model Nomenclature on
page 5 to confirm this unit's construction.
The metering devices are multiple fixed- - bore devices
(Acutrolt) swedged into the horizontal outlet tubes from
the liquid header, located at the entrance to each
evaporator coil circuit path. These are non- - adjustable.
Service requires replacing the entire liquid header
assembly.
To check for possible blockage of one or more of these
metering devices, disconnect the supply fan contactor
(IFC) coil, then start the compressor and observe the
frosting pattern on the face of the evaporator coil. A frost
pattern should develop uniformly across the face of the
Evaporator
Metering
NO Acutrol
YES Acutrol + TXV
NO Acutrol
YES TXV
coil starting at each horizontal header tube. Failure to
develop frost at an outlet tube can indicate a plugged or a
missing orifice.
THERMOSTATIC EXPANSION
VALVE (TXV)
All 48TC units equipped with Humidi- - MiZer option
include TXV control. On sizes 04- - 14, the TXV is located
in the liquid line between the Reheat Coil and the
standard Evaporator Coil (equipped with Acutrol devices).
On size 16 units equipped with the Humidi- - MiZer option,
each evaporator circuit
TXV- - distributor system; no Acutrols are included.
TXV Operation
The TXV is a metering device that is used in air
conditioning systems to adjust to the changing load
conditions by maintaining a preset superheat temperature
at the outlet of the evaporator coil. See Fig. 20.
The volume of refrigerant metered through the valve seat
is dependent upon the following:
1. Superheat temperature is sensed by the cap tube
sensing bulb on suction the tube at the outlet of
evaporator coil. This temperature 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 needle valve on the pin carrier is spring loaded,
exerting pressure on the underside of the diaphragm.
Therefore, the bulb pressure equals the evaporator
pressure (at the outlet of the coil) plus the spring
pressure. If the evaporator load increases, the
temperature increases at the bulb, which increases
the pressure on the topside of the diaphragm, pushing
the carrier away from the seat, opening the valve and
increasing the flow of refrigerant. The increased
refrigerant flow causes increased leaving evaporator
pressure which is transferred through the equalizer
tube to the underside of the diaphragm. This causes
the pin carrier spring pressure to close the TXV
valve. The refrigerant flow is effectively stabilized to
the load demand with a negligible change in
superheat.
13
is equipped with a