Bryant 548J Service And Maintenance Instructions page 63

position. Compressor 2 contactor (C2) is energized;
Compressor 2 starts and Circuit 2 operates in Cooling
mode.
When Cooling Stage 2 is satisfied, thermostat Y2 opens.
Compressor 2 contactor (C2) is de- - energized; Compressor
2 stops. RVS2 remains energized.
When Cooling Stage 1 is satisfied, thermostat Y1 opens.
Compressor 1 contactor (C1) is de- - energized; Compressor
1 stops. Outdoor fan relay OFR is de- - energized; outdoor
fans stop. After the Fan Delay period, the Indoor fan
contactor IFC is de- - energized; indoor fan stops (unless
Continuous Fan operation has been selected). RVS1
remains energized.
Reversing valve solenoids are energized in Cooling
modes. Each solenoid will remain energized until the
next Heating mode is initiated for this circuit.
Heating, Units Without Economizer
04A- - 07A (single compressor
thermostat calls for heating, terminal W1 is energized.
DFB receives this input at P2–7. The DFB removes the
output at P3–7 (RVS1)
de- - energized and reversing valve moves to Heating
position. DFB issues outputs at P3–9 (IFO), OF, and
P3–10 (COMP1). The indoor fan motor or contactor (IFC)
is energized; indoor fan motor starts. Outdoor fan relay
OFR is energized; outdoor fan motor runs. Compressor
contactor C1 is energized; refrigeration circuit operates in
Heating mode.
08D- - 09D (two compressor model): When the thermostat
calls for heating, terminal W1 is energized. DFB receives
this input at P2–7. The DFB removes the outputs at P3–7
(RVS1) and P3–6 (RVS2)); both reversing valve solenoids
are de- - energized and reversing valves move to Heating
position. DFB issues outputs at P3–9 (IFO), OF, P3–10
(COMP1) and P3–8 (COMP2)). The indoor fan contactor
(IFC) is energized; indoor fan motor starts. Outdoor fan
relay OFR is energized; both outdoor fan motors run.
Compressor contactors C1 and C2 are energized; both
refrigeration circuits operate in Heating mode.
If Stage 1 heating does not satisfy the space load, the
space temperature will fall until thermostat calls for Stage
2 heating (W2 closes). Terminal W2 is energized. DFB
receives input at P2- - 6. DFB issues an output at EHEAT.
Heater contactor 1 (HC1) and heater contactor 2 (HC2) (if
installed) are energized; all electric heaters are energized.
When space heating load is partially satisfied, thermostat
terminal W2 is de- - energized; this signal is removed at
DFB P2- - 6. DFB output at EHEAT is removed; heater
contactors HC1 and HC2 are de- - energized and all electric
heat is terminated. Stage 1 heating continues.
When the space heating load is fully satisfied, thermostat
terminal W1 is also de- - energized. DFB removes outputs
at P3- - 10 (COMP1), P3- - 8 (COMP2) and OF. All
compressor and outdoor fan operations cease. After the
Fan Delay period, output P3- - 9 is removed and IFM
operations cease (unless Continuous Fan operation has
been selected).
model): When the
reversing valve solenoid is
Reversing valve solenoids remain de- - energized until the
next call for Cooling mode is initiated.
Cooling, Unit With EconoMi$er IV
For Occupied mode operation of EconoMi$er IV, there
must be a 24- - v signal at terminal N (provided through
harness plug PL6- - 3 from the unit's IFC coil). Removing
the signal at N places the EconoMi$er IV control in
Unoccupied mode. During Occupied mode operation,
indoor fan operation will be accompanied by economizer
dampers moving to Minimum Position setpoint for
ventilation. If indoor fan is off, dampers will close. During
Unoccupied mode operation, dampers will remain closed
unless a Cooling (by free cooling) or DCV demand is
received.
When free cooling using outside air is not available, the
unit cooling sequence will be controlled directly by the
space thermostat as described above in Cooling, Unit
Without Economizer. Outside air damper position will be
closed or Minimum Position as determined by occupancy
mode and fan signal.
When free cooling is available as determined by the
appropriate changeover command (dry bulb, outdoor
enthalpy, differential dry bulb or differential enthalpy), a
call for cooling (Y1 closes at the thermostat, signal
through PL6- - 2 to Econo- - 1) will cause the economizer
control to modulate the dampers open and closed to
maintain the unit supply air temperature at 50_F to 55_F
(10_C to 12.8_C). Compressor will not run.
During free cooling operation, a supply air temperature
(SAT) above 50_F (10_C) will cause the dampers to
modulate between Minimum Position setpoint and 100%
open. With SAT from 50_F to 45_F (10_C to 7.2_C), the
dampers will maintain at the Minimum Position setting.
With SAT below 45_F (7.2_C), the outside air dampers
will be closed. When SAT rises to 48_F (8.9_C), the
dampers will re- - open to Minimum Position setting.
Should 100% outside air not be capable of satisfying the
space temperature, space temperature will rise until Y2 is
closed. The economizer control will call for compressor
operation. Y2 signal is transferred to the DFB's Y1 input
(P2- - 5). Stage 1 Cooling is initiated as described above in
Cooling, Unit Without Economizer.
modulate to maintain SAT at 50_F to 55_F (10_C to
12.8_C) concurrent with Compressor 1 operation. When
thermostat Stage 2 cooling is satisfied, DFB outputs for
COMP1 and OF will be removed and mechanical cooling
sequence will terminate.
The Low Ambient Lockout Thermostat will block
compressor operation with economizer operation below
42_F (5.6_C ) outside air temperature.
When space temperature demand is satisfied (thermostat
Y1 opens), the dampers will return to Minimum Damper
position if indoor fan is running or fully closed if fan is
off.
If accessory power exhaust is installed, the power exhaust
fan motors will be energized by the economizer control as
the dampers open above the PE- - On setpoint and will be
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Dampers will