Sequence Of Operation - Bryant Legacy Line Series Manual

SEQUENCE OF OPERATION

General
The sequence below describes the sequence of operation for an
electromechanical unit with and without a factory installed
EconoMi$er IV and X (called "economizer" in this sequence).
For information regarding a direct digital controller, see the
start-up, operations, and troubleshooting manual for the appli-
cable controller.
Electromechanical units with no economizer
Cooling (Single speed indoor fan motor)
When the thermostat calls for cooling, terminals G and Y1 are
energized. As a result, the indoor fan contactor (IFC) and the
compressor contactor (C1) are energized, causing the indoor
fan motor (IFM), compressor #1, and outdoor fan to start. If the
unit has 2 stages of cooling, the thermostat will additionally
energize Y2. The Y2 signal will energize compressor contactor
#2 (C2), causing compressor #2 to start. Regardless of the num-
ber of stages, the outdoor fan motor runs continuously while
unit is cooling. When SAV system is utilized, indoor fan motor
runs at design CFM (full speed) during the heating operation.
Heating (Single speed indoor fan motor)
When the thermostat calls for heating, power is sent to W on
the Integrated Gas Controller (IGC) board. An LED (light-
emitting diode) on the IGC board turns on and remains on
during normal operation. A check is made to ensure that the
rollout switch and limit switch are closed. If the check was suc-
cessful, the induced-draft motor is energized, and when its
speed is satisfactory, as proven by the "hall effect" sensor, the
ignition activation period begins. The burners will ignite within
5 seconds. If the burners do not light, there is a 22-second delay
before another 5-second attempt. This sequence is repeated for
15 minutes or until the burners light. If, after the 15 minutes,
the burners still have not lit, heating is locked out. To reset the
control, break 24-v power to the thermostat.
When ignition occurs, the IGC board will continue to monitor
the condition of the rollout switch, the limit switches, the "hall
effect" sensor, as well as the flame sensor. 45 seconds after
ignition occurs, assuming the unit is controlled through a room
thermostat set for fan auto, the indoor fan motor will energize
(and the outdoor air dampers will open to their minimum posi-
tion). If, for some reason, the over-temperature limit opens
prior to the start of the indoor fan blower, the unit will shorten
the 45-second delay to 5 seconds less than the time from initia-
tion of heat to when the limit tripped. Gas will not be inter-
rupted to the burners and heating will continue. Once the fan-
on delay has been modified, it will not change back to 45 sec-
onds until power is reset to the control.
On units with 2 stages of heat, when additional heat is required,
W2 closes and initiates power to the second stage of the main
gas valve. When the thermostat is satisfied, W1 and W2 open
and the gas valve closes, interrupting the flow of gas to the
main burners.
If the call for W1 lasted less than 1 minute, the heating cycle will
not terminate until 1 minute after W1 became active. If the unit is
controlled through a room thermostat set for fan auto, the indoor
fan motor will continue to operate for an additional 45 seconds
then stop. If the over-temperature limit opens after the indoor
motor is stopped, but within 10 minutes of W1 becoming inac-
tive, on the next cycle the time will be extended by 15 seconds.
The maximum delay is 3 minutes. Once modified, the fan off
44
delay will not change back to 45 seconds unless power is reset to
the control. A LED indicator is provided on the IGC to monitor
operation.
Electromechanical units with an economizer
Cooling
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 and X control to provide a 50°F (10°C) to 55°F (13°C)
mixed air temperature into the zone. As the mixed air tempera-
ture fluctuates above 55°F (13°C) or below 50°F (10°C) damp-
ers will be modulated (open or close) to bring the mixed air
temperature back within control. If mechanical cooling is uti-
lized with free cooling, the outdoor air damper will maintain its
current position at the time the compressor is started. If the
increase in cooling capacity causes the mixed air temperature
to drop below 45°F (7°C), then the outdoor air damper position
will be decreased to the minimum position. If the mixed air
temperature continues to fall, the outdoor air damper will close.
Control returns to normal once the mixed air temperature rises
above 48°F (9°C). The power exhaust fans will be energized
and de-energized, if installed, as the outdoor air damper opens
and closes.
If field-installed accessory CO
EconoMi$er IV and X control, a demand controlled ventilation
strategy will begin to operate. As the CO
increases above the CO setpoint, the minimum position of the
2
damper will be increased proportionally. As the CO
decreases because of the increase in fresh air, the outdoor air
damper will be proportionally closed. For EconoMi$er IV and
X operation, there must be a thermostat call for the fan (G).
If the unit is occupied and the fan is on, the damper will operate
at minimum position. Otherwise, the damper will be closed.
If field-installed accessory CO
EconoMi$er IV and X control, a demand controlled ventilation
strategy will begin to operate. As the CO
increases above the CO setpoint, the minimum position of the
2
damper will be increased proportionally. As the CO
decreases because of the increase in fresh air, the outdoor air
damper will be proportionally closed. For EconoMi$er IV and
X operation, there must be a thermostat call for the fan (G). If
the unit is occupied and the fan is on, the damper will operate at
minimum position. Otherwise, the damper will be closed.
When the EconoMi$er IV and X control is in the occupied
mode and a call for cooling exists (Y1 on the thermostat), the
control will first check for indoor fan operation. If the fan is not
on, then cooling will not be activated. If the fan is on, then the
control will open the EconoMi$er IV and X damper to the min-
imum position.
On the initial power to the EconoMi$er IV and X control, it
will take the damper up to 2
tion itself. After the initial power-up, further changes in damper
position can take up to 30 seconds to initiate. Damper move-
ment from full closed to full open (or vice versa) will take
between 1 1 / and 2 1 / minutes. If free cooling can be used as
2 2
determined from the appropriate changeover command
(switch, dry bulb, enthalpy curve, differential dry bulb, or dif-
ferential enthalpy), then the control will modulate the dampers
open to maintain the mixed air temperature setpoint at 50°F
(10°C) to 55°F (13°C). If there is a further demand for cooling
sensors are connected to the
2
level in the zone
2
sensors are connected to the
2
level in the zone
2
1 / minutes before it begins to posi-
2
level
2
level
2