54
2-Speed Note: When operating in ventilation mode only, the in-
door fan motor will automatically adjust to 66% of the total
cfm established.
Heating — The sequence of operation for the heating is the
same as an electro-mechanical unit with no economizer. The
only difference is how the economizer acts. The economizer
will stay at the Economizer Minimum Position while the evap-
orator fan is operating. The outdoor-air damper is closed when
the indoor fan is not operating.
Refer to Service and Maintenance Manual for further details.
Optional Perfect Humidity™ Dehumidification Sys-
tem —
Units with the factory equipped Perfect Humidity sys-
tem option are capable of providing multiple modes of im-
proved dehumidification as a variation of the normal cooling
cycle. The Perfect Humidity system option includes additional
valves in the liquid line and discharge line of each refrigerant
circuit, a small reheat condenser coil downstream of the evapo-
rator, and Motormaster
®
variable-speed control of some or all
outdoor fans. Operation of the revised refrigerant circuit for
each mode is described below.
The Perfect Humidity system provides three sub-modes of op-
eration: Cool, Reheat1, and Reheat2.
Cool mode
— Provides a normal ratio of Sensible and Latent
Cooling effect from the evaporator coil.
Reheat1
— Provides increased Latent Cooling while slightly
reducing the Sensible Cooling effect.
Reheat2
— Provides normal Latent Cooling but with null or
minimum Sensible Cooling effect delivered to the space.
The Reheat1 and Reheat2 modes are available when the unit is
not in a Heating mode and when the Low Ambient Lockout
switch is closed.
The figures on this page depict piping for single stage cooling
units.
RTU Open Controller (Factory Option) — For details on
operating 581J units equipped with the factory-installed RTU
Open controller option refer to Factory Installed RTU Open
Multi-Protocol Controller Controls, Start-Up, Operation and
Troubleshooting manual.
Minimum Operating Ambient Temperature (Cool-
ing) —
In mechanical cooling mode, your Bryant rooftop unit
can safely operate down to an outdoor ambient temperature of
35°F (2°C). It is possible to provide cooling at lower outdoor
ambient temperatures by using less outside air, economizers,
and/or accessory low ambient kits.
Maximum Operating Ambient Temperature (Cool-
ing) —
The maximum operating ambient temperature for
cooling mode is 125°F (52°C). While cooling operation above
125°F (52°C) may be possible, it could cause either a reduction
in performance, reliability, or a protective action by the unit’s
internal safety devices.
Minimum Mixed Air Temperature (Heating) — Using
the factory settings, the minimum temperatures for the mixed
air (the combined temperature of the warm return air and the
cold outdoor air) entering the dimpled, gas heat exchangers are
shown in the table below.
MINIMUM MIXED AIR TEMPERATURE
Operating at lower mixed-air temperatures may be possible, if a
field-supplied, outdoor air thermostat initiates both heat stages
when the temperature is less than the minimum temperatures
listed above. Please contact your local Bryant representative
for assistance.
NORMAL COOLING MODE — PERFECT HUMIDITY SYS-
TEM WITH SINGLE STAGE COOLING
CONDENSER COIL
PERFECT HUMIDITY COIL
EVAPORATOR COIL
COMPRESSOR
OUTDOOR AIR
INDOOR LEAVING
AIR
INDOOR ENTERING
AIR
RDV
VALVE
CLV
VALVE
REHEAT MODE
METERING
DEVICE (TXV)
= CLOSED VALVE
= OPEN VALVE
ALUMINIZED STAINLESS STEEL
50°F (10°C) Continuous 40°F (4°C) Continuous
45°F (7°C) Intermittent 35°F (2°C) Intermittent
SUBCOOLING MODE (REHEAT 1) — NORMAL COOLING
MODE — PERFECT HUMIDITY SYSTEM WITH SINGLE
STAGE COOLING
RDV
VALVE
CLV
VALVE
CONDENSER COIL
EVAPORATOR COIL
COMPRESSOR
OUTDOOR AIR
INDOOR LEAVING
AIR
INDOOR ENTERING
AIR
REHEAT MODE
METERING
DEVICE (TXV)
= CLOSED VALVE
= OPEN VALVE
PERFECT HUMIDITY COIL
HOT GAS REHEAT MODE (REHEAT2) — PERFECT
HUMIDITY SYSTEM WITH SINGLE STAGE COOLING
RDV
VALVE
CLV
VALVE
CONDENSER COIL
EVAPORATOR COIL
COMPRESSOR
OUTDOOR AIR
INDOOR LEAVING
AIR
INDOOR ENTERING
AIR
REHEAT MODE
METERING
DEVICE (TXV)
= CLOSED VALVE
= OPEN VALVE
PERFECT HUMIDITY COIL
SEQUENCE OF OPERATION (cont)
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