Specifications

56
CONTROLS
OPERATING SEQUENCE — 551B036-072 UNITS
Cooling, Units Without Economizer —
When the 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 the indoor (evaporator) fan motor
(IFM), compressor no. 1, and condenser fan start. The outdoor
(condenser) fan motor (OFM) runs continuously while unit is
cooling.
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 (cooling), the economizer
damper moves to the minimum position when the evaporator
fan starts. The first stage of cooling is provided by the econo-
mizer. 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 OFM will be deenergized. The damper position will be
determined by the supply-air temperature.
When the first stage of cooling is satisfied, there is a 30-second
delay before the evaporator fan shuts off on 048-060 units. The
damper will move to fully closed position.
Cooling, Units With EconoMi$er —
When the outdoor-air
temperature (OAT) is above the ECON SP set point and the
room thermostat calls for Stage 1 cooling (R to G + Y1), the
indoor (evaporator) fan motor (IFM) is energized and the
EconoMi$er damper modulates to minimum position. The com-
pressor contactor is energized to start the compressor and out-
door (condenser) fan motor (OFM). After the thermostat is
satisfied, the damper modulates to the fully closed position
when the IFM is deenergized.
When the OAT is below the ECON SP setting 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
greater than 57 F, the EconoMi$er modulates open, allowing a
greater amount of outdoor air to enter the unit. If the SAT drops
below 53 F, the outdoor air damper modulates closed to reduce
the amount of outdoor air. When the SAT is between 53 and
57 F, the EconoMi$er maintains its position.
If outdoor air alone cannot satisfy the cooling requirements of
the conditioned space, and the OAT is above the MECH CLG
LOCKOUT set point, the EconoMi$er integrates free cooling
with mechanical cooling. This is accomplished by the strategies
below.
NOTE:
Compressor has a 2-minute Minimum On, Minimum Off,
and Interstage delay timer.
1. If Y1 is energized, and the room thermostat calls for Y2
(2-stage thermostat), the compressor and OFM are ener-
gized. The position of the EconoMi$er damper is main-
tained at its current value.
2. If Y1 is energized for more than 20 minutes, and Y2 is not
energized (whether or not a 2-stage thermostat is used),
the compressor and OFM are energized. The position of the
EconoMi$er damper is maintained at its current value.
3. If Y1 is energized, and the compressor is already energized
(see Step 2) and the room thermostat calls for Y2, the com-
pressor continues to operate.
4. If the compressor is energized and the thermostat is satis-
fied, the compressor, the OFM, and IFM are deenergized
and the EconoMi$er modulates closed.
When the OAT is below the MECH CLG LOCKOUT set point,
the compressors remain off.
Heating, Units Without Economizer —
Upon a call for heating
through W1, indoor (evaporator) 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 con-
tactor no. 2 is energized through W2.
Heating, Units With Economizer —
When the room tempera-
ture calls for heat through terminal W1, the indoor (evaporator)
fan contactor (IFC) and heater contactor no. 1 (HC1) are ener-
gized. 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.
OPERATING SEQUENCE — 551B090-150 UNITS
Cooling, Units Without Economizer —
When the thermostat
calls for cooling, terminals G and Y1 are energized. The indoor
(evaporator) fan contactor (IFC), compressor contactor no. 1
(C1) and outdoor fan contactor (OFC) are energized and the
indoor (evaporator) fan motor (IFM), compressor no. 1, and con-
denser fans start. The outdoor (condenser) fan motors (OFM)
run continuously while unit is cooling. If the thermostat calls for
a second stage of cooling by energizing Y2, compressor con-
tactor no. 2 (C2) is energized and compressor no. 2 starts.
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 no. 1 is energized to start compressor
no. 1 and outdoor (condenser) 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.