Controls; Operating Sequence For 581B036-072 Units; Operating Sequence For 581B090-150 Units - Bryant COMMERCIAL SINGLE PACKAGE ROOFTOP GAS HEAT/ELECTRIC COOLING 581B User Manual

OPERATING SEQUENCE FOR 581B036-072 UNITS

Cooling, Units Without Economizer — When thermostat calls
for cooling, terminals G and Y1 and the compressor contactor
(C) are energized. The indoor (evaporator) fan motor (IFM),
compressor, and outdoor (condenser) fan motor (OFM) start.
The OFM runs continuously while the unit is in cooling. When
the thermostat is satisfied, C is deenergized and the compres-
sor and OFM shut off. After a 30-second delay, the IFM shuts
off. If the thermostat fan selector switch is in the ON position,
the evaporator motor will run continuously.
Cooling, Units With Durablade Economizer — When the
outdoor-air temperature is above the outdoor-air temperature
(OAT) setting and the room thermostat calls for cooling, the
compressor contactor is energized to start the compressor and
outdoor (condenser) fan motor (OFM). The indoor (evaporator)
fan motor (IFM) is energized and the economizer damper
moves to the minimum position. After the thermostat is satis-
fied, the damper moves to the fully closed position when IFM is
deenergized.
When the outdoor-air temperature is below the OAT setting and
the thermostat calls for Y1 and G, the economizer damper
moves to the minimum position when the evaporator fan starts.
The first stage of cooling is provided by the economizer. If the
supply-air temperature is above 57 F, a switch on the supply-air
thermostat is closed between the T2 terminal and the 24 vac
terminal. This causes the damper to continue to modulate open
until the supply-air temperature falls below 55 F or the damper
reaches the fully open position.
When the supply-air temperature is between 55 F and 52 F, the
supply-air thermostat has open switches between the T2 and
24 vac terminals and between the T1 and 24 vac terminals. This
causes the economizer damper to remain in an intermediate
open position.
If the supply-air temperature falls below 52 F, a switch on the
supply-air thermostat is closed between the T1 terminal and the
24 vac terminal. This causes the damper to modulate closed
until the supply-air temperature rises above 55 F or the damper
reaches the minimum position.
When the supply-air temperature is between 55 F and 57 F, the
supply-air thermostat has open switches between the T2 and
24 vac terminals. This causes the economizer damper to
remain in an intermediate open position.
If the outdoor air alone cannot satisfy the cooling requirements
of the conditioned space, economizer cooling is integrated with
mechanical cooling, providing second stage cooling. The com-
pressor and condenser fan will be energized and the position of
the economizer damper will be determined by the supply-air
temperature.
When the second stage of cooling is satisfied, the compressor
and condenser-fan motor will be deenergized. The damper
position will be determined by the supply-air temperature.
When the first stage of cooling is satisfied, the IFM shuts off
after a 30-second delay. The damper then moves to fully closed
position.
Cooling, Units With EconoMi$er — When the outdoor-air
temperature (OAT) is above the ECON SP set point and the
room thermostat calls for Stage 1 cooling (R to G +Y1), the
indoor-fan motor (IFM) is energized and the EconoMi$er
damper modulates to minimum position. The compressor con-
tactor is energized starting the compressor and outdoor-fan
motor (OFM). After the thermostat is satisfied, the damper mod-
ulates to the fully closed position when the IFM is deenergized.
When the OAT is below the ECON SP set point and the room
thermostat calls for Stage 1 cooling (R to G + Y1), the
EconoMi$er modulates to the minimum position when the IFM
is energized. The EconoMi$er provides Stage 1 of cooling by
modulating the return and outdoor air dampers to maintain a
55 F supply air set point. If the supply-air temperature (SAT) is

CONTROLS

greater than 57 F, the EconoMi$er modulates open, allowing a
greater amount of outdoor air to enter the unit. If the SAT drops
below 53 F, the outdoor-air damper modules closed to reduce
the amount of outdoor air. When the SAT is between 53 and
57 F, the EconoMi$er maintains its position.
Heating, Units Without Economizer — When the thermostat
calls for heating, terminal W1 is energized. The induced-draft
motor is energized and the burner ignition sequence begins.
The indoor (evaporator) fan motor (IFM) is energized 45 sec-
onds after a flame is ignited. On units equipped for two stages
of heat, when additional heat is needed, W2 is energized and
the high-fire solenoid on the main gas valve (MGV) is ener-
gized. When the thermostat is satisfied and W1 is deenergized,
the IFM stops after a 45-second time-off delay.
Heating, Units With Economizer or Two-Position Damper —
When the thermostat calls for heating, terminal W1 is ener-
gized. The induced-draft motor is energized and the burner igni-
tion sequence begins. The indoor (evaporator) fan motor (IFM)
is energized 45 seconds after a flame is ignited and the damper
moves to the minimum position. If the accessory two-position
damper is used, the outdoor-air damper opens to the minimum
position whenever the evaporator fan runs. On units equipped
for two stages of heat, when additional heat is needed, W2 is
energized and the high-fire solenoid on the main gas valve
(MGV) is energized. When the thermostat is satisfied and W1 is
deenergized, the IFM stops after a 45-second time-off delay.
The economizer damper then moves to the fully closed position.
When using continuous fan, the damper will remain in the mini-
mum position.

OPERATING SEQUENCE FOR 581B090-150 UNITS

Cooling, Units Without Economizer — When thermostat calls
for cooling, terminals G and Y1 are energized. The indoor
(evaporator) fan contactor (IFC) and compressor contactor no. 1
(C1) are energized, and evaporator-fan motor, compressor
no. 1, and condenser fans start. The condenser-fan motors run
continuously while unit is cooling. For units with 2 stages of
cooling, if the thermostat calls for a second stage of cooling by
energizing Y2, compressor contactor no. 2 (C2) is energized
and compressor no. 2 starts.
When the thermostat is satisfied, C1 and C2 are deenergized
and the compressors and outdoor (condenser) fan motors
(OFM) shut off. After a 30-second delay, the indoor (evaporator)
fan motor (IFM) shuts off. If the thermostat fan selector switch is
in the ON position, the evaporator motors will run continuously.
Cooling, Units With Durablade Economizer — When the
outdoor-air temperature (OAT) is above the OAT setting and the
room thermostat calls for cooling, the compressor contactor
no. 1 is energized to start compressor no. 1 and outdoor (con-
denser) fan motors (OFM). The indoor (evaporator) fan motor
(IFM) is energized and the economizer damper moves to the
minimum position. Upon a further call for cooling, compressor
contactor no. 2 will be energized, starting compressor no. 2.
After the thermostat is satisfied and the IFM is deenergized, the
damper moves to the fully closed position.
When the outdoor-air temperature is below the OAT setting and
the thermostat calls for Y1 and G, the economizer damper
moves to the minimum position when the evaporator fan starts.
The first stage of cooling is provided by the economizer. If the
supply-air temperature is above 57 F, a switch on the supply-air
thermostat is closed between the T2 terminal and the 24 vac
terminal. This causes the damper to continue to modulate open
until the supply-air temperature falls below 55 F or the damper
reaches the fully open position.
When the supply-air temperature is between 55 F and 52 F, the
supply-air thermostat has open switches between the T2 and
24 vac terminals and between the T1 and 24 vac terminals. This
causes the economizer damper to remain in an intermediate
open position.
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