Controls - Carrier 50ZH Product Data

Typical wiring schematic (cont)

Controls

Sequence of operation
When power is supplied to unit, the transformer (TRAN) is
energized.
Cooling — With the thermostat subbase in the cooling po-
sition, and when the space temperature comes within 2° F
of the cooling set point, the thermostat makes circuit R-O.
This energizes the reversing valve solenoid (RVS) and places
the unit in standby condition for cooling.
As the space temperature continues to rise, the second
stage of the thermostat makes, closing circuit R-Y. When
compressor time delay (5 ± 2 minutes) is completed, a cir-
cuit is made to contactor (C), starting the compressor (COMP)
and outdoor-fan motor (OFM). Circuit R-G is made at the
same time, energizing the indoor-fan relay (IFR) and start-
ing the indoor-fan motor (IFM) after a 1-second delay.
When the thermostat is satisfied, contacts open, deener-
gizing C. The COMP and OFM stop, and the IFM stops
after a 30-second delay.
Heating — On a call for heat, thermostat makes circuits
R-Y and R-G.
ELECTRIC HEATER WIRING
When compressor time delay (5 ± 2 minutes) is com-
pleted, a circuit is made to C, starting COMP and OFM.
Circuit R-G also is completed, energizing IFR and starting
IFM after a 1-second delay.
Should room temperature continue to fall, circuit R-W is
made through second-stage thermostat bulb. If optional elec-
tric heat package is used, a relay is energized, bringing on
first bank of supplemental electric heat. When thermostat
is satisfied, contacts open, deenergizing contactor and re-
lay; motors and heaters deenergize. The IFM may be con-
trolled by a time-delay relay that keeps the fan on for
30 seconds.
Defrost — Defrost board (DB) is a time and temperature
control, which includes a field-selectable time period be-
tween checks for defrost (30, 50, and 90 minutes). Elec-
tronic timer and defrost cycle start only when contactor is
energized and defrost thermostat (DFT) is closed.
Defrost mode is identical to cooling mode, except outdoor-
fan motor stops and a bank of optional electric heat turns
on to warm air supplying the conditioned space.
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