Liquid Line Filter Drier; Suction Line Filter Drier; Thermostatic Expansion Valve (Txv) - Carrier 25VNA Service Manual

Liquid Line Filter Drier

Filter driers are specifically designed for R- -22 or Puronr
refrigerant. Only operate with the appropriate drier using factory
authorized components.
It is recommended that the liquid line drier be installed at the
indoor unit. Placing the drier near the TXV allows additional
protection to the TXV as the liquid line drier also acts as a strainer.
CAUTION
!
UNIT DAMAGE HAZARD
Failure to follow this caution may result in equipment damage
or improper operation.
To avoid performance loss and compressor failure, installation
of filter drier in liquid line is required.
CAUTION
!
UNIT DAMAGE HAZARD
Failure to follow this caution may result in equipment damage
or improper operation.
To avoid filter drier damage while brazing, filter drier must be
wrapped in a heat- -sinking material such as a wet cloth.
Install Liquid- -line Filter Drier Indoor - - HP
Refer to Fig. 31 and install filter drier as follows:
1. Braze 5 in. liquid tube to the indoor coil.
2. Wrap filter drier with damp cloth.
3. Braze filter drier to 5 in. long liquid tube from step 1.
4. Connect and braze liquid refrigerant tube to the filter drier.

Suction Line Filter Drier

The suction line drier is specifically designed to operate with
Puronr, use only factory authorized components. Suction line filter
drier is used in cases where acid might occur, such as burnout. Heat
pump units must have the drier installed between the compressor
and accumulator only. Remove after 10 hours of operation. Never
leave suction line filter drier in a system longer than 72 hours
(actual time).
Fig. 31 – Liquid Line Filter Drier - - HP

Thermostatic Expansion Valve (TXV)

All fan coils and furnace coils will have a factory installed
thermostatic expansion valve (TXV). The TXV will be a bi- -flow,
hard- -shutoff with an external equalizer and a balance port pin. A
hard shut- -off TXV does not have a bleed port.
minimal equalization takes place after shutdown.
specifically designed to operate with Puronr or R- -22 refrigerant,
use only factory authorized TXV's. Do not interchange Puron
and R- -22 TXVs.
TXV Operation
The TXV is a metering device that is used in air conditioning 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 the following:
1. Superheat temperature is sensed by cap tube sensing bulb
on suction tube at outlet of evaporator coil. This
temperature is converted into pressure by refrigerant in the
bulb pushing downward on the diaphragm which opens the
valve via the push rods.
2. The suction pressure at the outlet of the evaporator coil is
transferred via the external equalizer tube to the underside
of the diaphragm. This is needed to account for the indoor
coil pressure drop. Residential coils typically have a high
pressure drop, which requires this valve feature.
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 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 negligible change in superheat.
A05227
36
Therefore,
TXVs are