13
Refrigerant Charge
The amount of refrigerant charge is listed on the unit’s
nameplate. Refer to Carrier Publication, “GTAC2--5
Charging, Recovery, Recycling and Reclamation Training
Manual” and the following procedures:
Unit panels must be in place when unit is operating during
the charging procedure. If unit is equipped with a head
pressure control device, bypass it to ensure full fan
operation during charging.
Charge checking and adjustments must be made while the
system is operating in Cooling only.
No Charge:
Use standard evacuation techniques for Puron (R--410A)
refrigerant.. After evacuating system, weigh the specified
amount of refrigerant.
THERMOSTATIC EXPANSION VALVE
(TXV)
All 50TCQ’s have a factory installed nonadjustable
thermostatic expansion valve (TXV). The TXV will be a
bi-flow, bleed port expansion valve with an external
equalizer. TXVs are specifically designed to operate with
Puron
R
refrigerant, use only factory authorized TXVs.
See Fig. 15 for a typical piping schematic.
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 (see Fig. 17):
1. Superheat temperature is sensed by the cap tube sens-
ing bulb on the suction tube at outlet of the evaporat-
or coil. This temperature is converted into pressure by
refrigerant in the bulb pushing downward on the dia-
phragm which opens the valve using the push rods.
As long as this bulb and cap tube contain any liquid
refrigerant, this temperature is converted into suction
pressure pushing downward on the diaphragm, which
tends to open the TXV valve through 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 evaporator pres-
sure (at outlet of coil) plus spring pressure. If the load
increases, the temperature increases at the bulb,
which increases the pressure on the top side of the
diaphragm, pushing the carrier away from the seat,
opening the valve and increasing the flow of refriger-
ant. The increased refrigerant flow causes increased
leaving evaporator pressure which is transferred
through the equalizer tube to the underside of the dia-
phragm. This causes pin carrier spring pressure to
close the TXV valve. The refrigerant flow is effect-
ively stabilized to the load demand with a negligible
change in superheat.
OUTLET
INLET
PUSHRODS
DIAPHRAGM
NEEDLE
VALVE
SPRING
DISTRIBUTOR
FEEDER TUBES
CAPILLARY TUBE
COIL
BULB
EXTERNAL EQUALIZER TUBE
C12046
Fig. 17 -- Thermostatic Expansion Valve (TXV) Operation
Summary of Contents for WeatherMaster 50HCQA04
Page 38: ...38 C10818 Fig 56 RTU OPEN Control Module ...
Page 78: ...78 APPENDIX V WIRING DIAGRAMS C150427 Fig 58 50HCQA04 A05 Control Wiring Diagram 575 3 60 ...
Page 80: ...80 APPENDIX V WIRING DIAGRAMS C160013 Fig 60 50HCQ 06 Control Wiring Diagram 575 3 60 ...
Page 84: ...84 APPENDIX V WIRING DIAGRAMS C150243 Fig 64 50HCQ 04 05 06 Power Wiring Diagram 208 230 1 60 ...
Page 85: ...85 APPENDIX V WIRING DIAGRAMS C12347 Fig 65 50HCQ 04 05 06 Power Wiring Diagram 208 230 3 60 ...
Page 86: ...86 APPENDIX V WIRING DIAGRAMS C12353 Fig 66 50HCQ 04 05 06 Power Wiring Diagram 460 3 60 ...
Page 87: ...87 APPENDIX V WIRING DIAGRAMS C12354 Fig 67 50HCQ 04 05 06 Power Wiring Diagram 575 3 60 ...
Page 91: ...91 APPENDIX V WIRING DIAGRAMS C12356 Fig 71 50HCQ 12 Power Wiring Diagram 460 3 60 575 3 60 ...
Page 92: ...92 APPENDIX V WIRING DIAGRAMS C150432 Fig 72 50HCQ PremierLink Control Diagram ...
Page 93: ...93 APPENDIX V WIRING DIAGRAMS C12359 Fig 73 50HCQ RTU Open Control Diagram ...