18
THERMOSTATIC EXPANSION VALVE
(TXV)
All 48/50HC’s have factory installed nonadjustable
thermostatic expansion valves (TXV). The TXVs are
bleed port expansion valve with an external equalizer.
TXVs are specifically designed to operate with Puron
R
or
R-22 refrigerant. Use only factory authorized TXVs. See
Fig. 18.
OUTLET
INLET
PUSHRODS
DIAPHRAGM
NEEDLE
VALVE
SPRING
DISTRIBUTOR
FEEDER TUBES
CAPILLARY TUBE
COIL
BULB
EXTERNAL EQUALIZER TUBE
Fig. 21 -- Thermostatic Expansion Valve (TXV) Operation
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.
See Fig. 23.
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.
Replacing TXV
PERSONAL INJURY HAZARD
Failure to follow this caution can result in injury to
personnel and damage to components..
Always wear approved safety glasses, work gloves
and
other
recommended
Personal
Protective
Equipment (PPE) when working with refrigerants.
CAUTION
!
1. Disconnect all AC power to unit. Use approved
lockout/tagout procedures.
2. Using gauge set approved for use with Puron
(R--410A) refrigerant, recover all refrigerant from the
system..
3. Remove TXV support clamp.
4. Disconnect the liquid line at the TXV inlet.
5. Remove the liquid line connection at the TXV inlet.
6. Remove equalizer tube from suction line of coil. Use
tubing
cutter
to
cut
brazed
equalizer
line
approximately 2--inches (50 mm) above the suction
tube.
7. Remove bulb from vapor tube above the evaporator
coil header outlet.
8. Install the new TXV avoiding damage to the tubing or
the valve when attaching the TXV to the distributor.
Protect the TXV against over--temperature conditions
y using wet rags and directing the torch flame tip
away from the TXV body. Connect the liquid line to
the TXV inlet by repeating the above process.
9. Attach the equalizer tube to the suction line. If the
replacement TXV has a flare nut on its equalizer line,
48H
C
Summary of Contents for 48HC D17 Series
Page 77: ...77 APPENDIX IV WIRING DIAGRAMS C12616 Fig 77 48HC D17 D28 Power Diagram 208 230 3 60 48HC...
Page 78: ...78 APPENDIX IV WIRING DIAGRAMS C12617 Fig 78 48HC D17 D28 Power Diagram 460 3 60 48HC...
Page 79: ...79 APPENDIX IV WIRING DIAGRAMS C12618 Fig 79 48HC D17 D28 Power Diagram 575 3 60 48HC...
Page 86: ...86 APPENDIX IV WIRING DIAGRAMS C13767 Fig 86 RTU OPEN Wiring Diagram 48HC...
Page 87: ...87 APPENDIX IV WIRING DIAGRAMS C13768 Fig 87 RTU OPEN Wiring Diagram with Humidi MiZer 48HC...
