Bryant 549B User Manual
Page 35
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35
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VIII. COOLING
To start the unit, turn on main power supply. Set the system
selector switch at COOL position and fan switch at AUTO
position. Adjust the thermostat to a setting below room
temperature. The compressor, reversing valve, outdoor-fan
contactor and indoor blower motor are energized.
Check the unit charge. Refer to Refrigerant Charge section
on page 37.
Reset the thermostat at a position above room temperature.
The compressor will shut off.
A. To Shut Off Unit
Set the system selector switch at OFF position. Resetting the
thermostat at a position above room temperature shuts unit
off temporarily until the space temperature exceeds the ther-
mostat setting.
Compressor restart is accomplished by manual reset at the
thermostat by turning the selector switch to OFF position
and then ON position.
IX. HEATING
To start the unit, turn on the main power supply.
Set thermostat at HEAT position and a setting above room
temperature, and set fan at AUTO. position.
The first stage of the thermostat energizes the indoor fan
motor, compressor, and outdoor fan; the second stage ener-
gizes the electric heater elements if installed. Check heating
effects at air supply grille(s).
If accessory electric heaters do not energize, reset the limit
switch (located on indoor-fan scroll) by pressing the button
located between the terminals on the switch.
A. To Shut Off Unit
Set the system selector switch at OFF position. Resetting the
heating selector lever below room temperature temporarily
shuts the unit off until the space temperature falls below the
thermostat setting.
X. SAFETY RELIEF
A soft solder joint in the suction line at the loss-of-charge/
low-pressure switch fitting provides pressure relief under
abnormal temperature and pressure conditions.
XI. VENTILATION (Continuous Fan)
Set the fan and system selector switches at ON and OFF
positions, respectively. The indoor fan operates continuously
to provide constant air circulation.
XII. OPERATING SEQUENCE
A. Cooling, Units without Economizer
When thermostat calls for cooling, terminals G and Y1 are
energized. The indoor-fan contactor (IFC), reversing valve
solenoid (RVS1) and compressor contactor no. 1 (C1) are
energized and indoor-fan motor, compressor no. 1, and out-
door fan(s) starts. The outdoor-fan motor(s) runs continu-
ously while unit is cooling. If the thermostat calls for a
second stage of cooling by energizing Y2, compressor contac-
tor no. 2 (C2) and reversing valve solenoid (RVS2) are ener-
gized and compressor no. 2 starts.
B. Heating, Units without Economizer
Upon a request for heating from the space thermostat, ter-
minal W1 will be energized with 24 v. The IFC, outdoor-fan
contactor (OFC), C1, and C2 will be energized. The reversing
valves switch position and the indoor fan, outdoor fan(s),
compressor no. 1, and compressor no. 2 are energized.
If the space temperature continues to fall while W1 is
energized, W2 will be energized with 24 v, and the heater
contactor(s) (HC) will be energized, which will energize the
electric heater(s).
When the space thermostat is satisfied, W2 will be deener-
gized first, and the electric heater(s) will be deenergized.
Upon a further rise in space temperature, W1 will be
deenergized, and the reversing valve solenoids (RVS1 and
RVS2) will be energized.
C. Cooling, Units With EconoMi$er IV
When free cooling is not available, the compressors will be
controlled by the zone thermostat. When free cooling is avail-
able, the outdoor-air damper is modulated by the
EconoMi$er IV control to provide a 50 to 55 F supply-air
temperature into the zone. As the supply-air temperature
fluctuates above 55 or below 50 F, the dampers will be modu-
lated (open or close) to bring the supply-air temperature
back within the set point limits.
For EconoMi$er IV operation, there must be a thermostat
call for the fan (G). This will move the damper to its mini-
mum position during the occupied mode.
Above 50 F supply-air temperature, the dampers will modu-
late from 100% open to the minimum open position. From
50 F to 45 F supply-air temperature, the dampers will main-
tain at the minimum open position. Below 45 F the dampers
will be completely shut. As the supply-air temperature rises,
the dampers will come back open to the minimum open posi-
tion once the supply air temperature rises to 48 F.
If optional power exhaust is installed, as the outdoor-air
damper opens and closes, the power exhaust fans will be
energized and deenergized.
If field-installed accessory CO
2
sensors are connected to the
EconoMi$er IV control, a demand controlled ventilation
strategy will begin to operate. As the CO
2
level in the zone
increases above the CO
2
set point, the minimum position of
the damper will be increased proportionally. As the CO
2
level
decreases because of the increase in fresh air, the outdoor-air
damper will be proportionally closed. Damper position will
follow the higher demand condition from DCV mode or free
cooling mode.
Damper movement from full closed to full open (or vice
versa) will take between 1
1
/
2
and 2
1
/
2
minutes.
If free cooling can be used as determined from the appropri-
ate changeover command (switch, dry bulb, enthalpy curve,
differential dry bulb, or differential enthalpy), a call for cool-
ing (Y1 closes at the thermostat) will cause the control to
modulate the dampers open to maintain the supply air tem-
perature set point at 50 to 55 F.
As the supply-air temperature drops below the set point range
of 50 to 55 F, the control will modulate the outdoor-air damp-
ers closed to maintain the proper supply-air temperature.
D. Heating, Units with EconoMi$er IV
When the room temperature calls for heat through terminal
W1, the indoor fan contactor (IFC) and heater contactor no. 1
(HC1) are energized. On units equipped for 2 stages of heat,
when additional heat is needed, heater contactor no. 2 is
energized through W2. The economizer damper moves to the
minimum position. When the thermostat is satisfied, the
damper moves to the fully closed position.