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TO SHUT OFF UNIT — Set system selector switch at OFF
position. Resetting thermostat at a position above room tem-
perature shuts unit off temporarily until space temperature ex-
ceeds thermostat setting. Units are equipped with Cycle-
LOC™ protection device. Unit shuts down on any safety trip
and remains off; an indicator light on the thermostat comes on.
Check reason for safety trip.
Compressor restart is accomplished by manual reset at the
thermostat by turning the selector switch to OFF position and
then ON position.
Heating (If Accessory Heater is Installed) —
To
start unit, turn on main power supply.
Set thermostat at HEAT position and a setting above room
temperature, and set fan at AUTO position.
First stage of thermostat energizes the first-stage electric
heater elements; second stage energizes second-stage electric
heater elements. Check heating effects at air supply grille(s).
If accessory electric heaters do not energize, reset limit
switch (located on evaporator-fan scroll) by pressing button lo-
cated between terminals on the switch.
TO SHUT OFF UNIT — Set system selector switch at OFF
position. Resetting heating selector lever below room tempera-
ture temporarily shuts unit off until space temperature falls be-
low thermostat setting.
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.
Ventilation (Continuous Fan) —
Set fan and system
selector switches at ON and OFF positions, respectively.
Evaporator fan operates continuously to provide constant air
circulation.
Operating Sequence
COOLING, UNITS WITHOUT ECONOMIZER — When
the thermostat calls for cooling, terminals G and Y1 are ener-
gized. The indoor (evaporator) fan contactor (IFC) and com-
pressor contactor no. 1 (C1) are energized and the evaporator-
fan motor, compressor no. 1, and condenser fans start. The con-
denser-fan motors run continuously while unit is in cooling. If
the thermostat calls for a second stage of cooling by energizing
Y2, compressor contactor no. 2 (C2) is energized and compres-
sor no. 2 starts.
HEATING, UNITS WITHOUT ECONOMIZER (If Acces-
sory Heater is Installed) — Upon a call for heating through
terminal W1, IFC and heater contactor no. 1 (HC1) are ener-
gized. On units equipped for 2 stages of heat, when additional
heat is needed, HC2 is energized through W2.
COOLING, UNITS WITH ECONOMI$ER IV — When free
cooling is not available, the compressors will be controlled by
the zone thermostat. When free cooling is available, the
outdoor-air damper is modulated by the EconoMi$er IV con-
trol 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 modulated (open or close) to
bring the supply-air temperature back within the set point
limits.
For EconoMi$er IV operation, there must be a thermostat
call for the fan (G). This will move the damper to its minimum
position during the occupied mode.
Above 50 F supply-air temperature, the dampers will modu-
late from 100% open to the minimum open position. From 50 F
to 45 F supply-air temperature, the dampers will maintain at
the minimum open position. Below 45 F the dampers will be
completely shut. As the supply-air temperature rises, the damp-
ers will come back open to the minimum open position once
the supply air temperature rises to 48 F.
If optional power exhaust is installed, as the outdoor-air
damper opens and closes, the power exhaust fans will be ener-
gized and deenergized.
If field-installed accessory CO
2
sensors are connected to the
EconoMi$er IV control, a demand controlled ventilation strate-
gy 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 high-
er 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 cooling
(Y1 closes at the thermostat) will cause the control to modulate
the dampers open to maintain the supply air temperature 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
dampers closed to maintain the proper supply-air temperature.
HEATING, UNITS WITH ECONOMI$ER IV — When the
room temperature calls for heat, the heating controls are ener-
gized as described in the Heating, Units Without Economizer
section. When the thermostat is satisfied, the economizer
damper moves to the minimum position.
COOLING, UNITS WITH ECONOMI$ER2, PREMIER-
LINK™ CONTROL AND A THERMOSTAT — When free
cooling is not available, the compressors will be controlled by
the PremierLink control in response to the Y1 and Y2 inputs
from the thermostat.
The PremierLink control will use the following information
to determine if free cooling is available:
• Indoor fan has been on for at least 30 seconds.
• The SPT, SAT, and OAT inputs must have valid readings.
• OAT must be less than 75 F.
• OAT must be less than SPT.
• Enthalpy must be LOW (may be jumpered if an enthalpy
sensor not available).
• Economizer position is NOT forced.
Pre-cooling occurs when there is no call from the thermostat
except G. Pre-cooling is defined as the economizer modulates
to provide 70 F supply air.
When free cooling is available the PremierLink control will
control the compressors and economizer to provide a supply-
air temperature determined to meet the Y1 and Y2 calls from
the thermostat using the following three routines. The three
control routines are based on OAT.
The 3 routines are based on OAT where:
SASP = Supply Air Set Point
DXCTLO = Direct Expansion Cooling Lockout Set Point
PID = Proportional Integral
Routine 1
(OAT < DXCTLO)
• Y1 energized – economizer maintains a SASP =
( 3).
• Y2 energized – economizer maintains a SASP =
( 3).
Routine 2
(DXCTLO < OAT < 68 F)
• If only Y1 energized, the economizer maintains a SASP
= ( 3).
• If SAT > SASP + 5 and economizer position > 80%,
economizer will go to minimum position for 3 minutes or
until SAT > 68 F.
• First stage of mechanical cooling will be energized.
• Integrator resets.
