Bryant 575B - Manual (Page 2)

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SEQUENCE OF OPERATION —
575B OUTDOOR UNIT WITH
524A-H INDOOR UNIT
When power is supplied to unit, the transformer (TRAN) and
crankcase heater (CCH) are energized.
Cooling
On a call for cooling, the thermostat completes the following
circuits: R-G, R-Y, and R-O. If the compressor recycle delay of
3 minutes is complete, the compressor and outdoor fan start.
The reversing valve is energized for cooling and the indoor-
fan motor starts.
When the thermostat is satisfied, the circuits are opened,
and the compressor, outdoor-fan motor, and indoor-fan motor
stop. The reversing valve is deenergized.
Heating
On a call for heating, the thermostat completes the following
circuits: R-G and R-Y. If the compressor recycle delay of
3 minutes is complete, the compressor and outdoor fan start.
The indoor-fan motor will also start.
If room temperature continues to fall, the thermostat com-
pletes circuit R-W. If the optional electric heat package is
used, the heat relay is energized, and the electric heaters are
energized.
When the thermostat is satisfied, the circuits are opened,
and the compressor, outdoor-fan motor, heaters, and indoor-
fan motor stop.
Defrost
The Defrost board (DB) is a time and temperature control,
which includes a field-selectable time period between checks
for frost (30, 50, and 90 minutes). Electronic timer and
defrost cycle start only when contactor is energized and
defrost thermostat (DFT) is closed (below 36 F [2.2 C]).
Defrost mode is identical to Cooling mode, except outdoor-fan
motor (OFM) stops and a bank of supplemental electric heat
(if equipped) turns on to warm air supplying the conditioned
space. Defrost mode is terminated when the DFT reaches
51 F (10.6 C).
Low Ambient
Cooling head pressure control at low ambient conditions is
accomplished through a low ambient relay and switch. The
switch is factory set to close at 250 psig and open at 100 psig.
In Heating mode, the low ambient switch is bypassed by nor-
mally closed contacts on the low ambient relay.
Air Circulation
When the fan switch is at FAN ON, the indoor-air fans oper-
ate continuously to provide ventilation. The thermostat oper-
ates the other components as described above.
Emergency Heat Cycle
If the compressor is inoperative due to a tripped safety
device, the second stage of the thermostat automatically
energizes the indoor-air fan and the electric resistance heat-
ers (if equipped).
SEQUENCE OF OPERATION —
575C OUTDOOR UNIT WITH
524A-H INDOOR UNIT
When power is supplied to unit, the transformer (TRAN) is
energized. The crankcase heater is also energized.
Cooling
With the thermostat in the cooling position, and when the
space temperature comes within 2° F of the cooling set point,
the thermostat makes circuit R-O. This energizes the revers-
ing valve solenoid (RVS) and places the unit in standby con-
dition for cooling.
As the space temperature continues to rise, the second stage
of the thermostat makes, closing circuit R-Y. When compres-
sor time delay (5 ± 2 minutes) is completed, a circuit 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 contactor (IFC) and starting
the indoor-fan motor (IFM) after one-second delay.
When the thermostat is satisfied, contacts open, deenergiz-
ing C. The COMP, IFM, and OFM stop.
Heating
On a call for heat, thermostat makes circuits R-Y and R-G.
When compressor time delay (5 ± 2 minutes) is completed, a
circuit is made to C, starting COMP and OFM. Circuit R-G
also energizes IFC and starts 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
supplemental electric heat. When thermostat is satisfied,
contacts open, deenergizing contactor and relay; motors and
heaters deenergize.
Defrost
Defrost board (DB) is a time and temperature control, which
includes a field-selectable time period between checks for
frost (30, 50, and 90 minutes). Electronic timer and defrost
cycle start only when contactor is energized and defrost ther-
mostat (DFT) is closed (below 28 F [–2.2 C]).
Defrost mode is identical to Cooling mode, except outdoor-fan
motor (OFM) stops and a bank of supplemental electric heat
turns on to warm air supplying the conditioned space.
Defrost mode is terminated when the DFT reaches 65 F
(18.3 C).