Operating Sequence
COOLING. UNITS WITHOUT ECONOMIZER --When
thermostat calls for cooling, termimds G and YI ale energized.
The indoor (evaporator) fan contactor (IFC), outdoor fan contac-
tot (OFC), and compressor contactor no. 1 (CI) m'e energized
and evaporator-fan motol: condenser fans and compressor no. 1
stall. The condenser-fan motors run continuously while unit is
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.
HEATING. UNITS WITHOUT ECONOMIZER (If Optional
or Accessory Heater is Installed) --Upon a call for heating
through terminal WI, IFC and heater contactor no. 1 (HCI) are
energized. On units equipped for 2 stages of heat, when addi-
tional heat is needed HC2 is energized through W2.
COOLING. UNITS WITH ECONOMISERIV --When free
cooling is not available, the compressors will be controlled by
the zone themlostat. When free cooling is available, the
outdoor-air &unper is modulated by the EconoMiSeriv control
to provide a 50 to 55 F supply-air temperature into the zone. As
the supply-air temperature fluctuates above 55 or below 50 IF.
the dampel.'s will be modulated (open or close) to bring the sup-
ply-air temperature back within set point limits.
For EconoMiSerIV 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 dmnpers will modu-
late from 100% open to the minimum open position. From 50 F
to 45 F supply-air temperature, the cktmpers 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 E
If optional power exhaust is inst_dled, as the outdoor-air
damper opens and closes, the power exhaust fans will be ener-
gized and deenergized.
If field-installed accessory CO2 sensors are connected to the
EconoMiSer IV control, a demand controlled ventilation strate-
gy will begin to operate. As the CO,_ level in the zone increases
above the CO2 set point, the minimum position of the &tmper
will be increased proportionally. As the CO2 level decreases
because of the increase in fresh all: the outdoor-air damper will
be proportionally closed. Dmnper 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
vel.sa) will take between 11/2and 21/2 minutes.
If free cooling can be used as determined from the appropri-
ate changeover command (switch, diy bulb, enthalpy curve,
differential dry bulb, or differential enthalpy), a call for cooling
(YI closes at the thermostat) will cause the control to modulate
the &tmpel.s open to maintain the supply air temperature set
point at 50 to 55 E
As the supply-air temperature diops below the set point
range of 50 to 55 E the control will modulate the outdoor-air
dampers closed to maintain the proper supply-air temperature.
HEATING, UNITS WITH ECONOMISERIV -- When the
room temperature calls for heat, the heating controls are ener-
gized as described in the Heating, Units Without Economizer
section. When the indoor fan is energized, the economizer
damper moves to the minimum position. When the indoor fan
is off. the economizer dmnper is fully closed.
COOLING. UNITS WITH ECONOMISER2, PREMIER-
LINK TM CONTROL AND A THERMOSTAT -- When free
cooling is not available, the complessors will be controlled by
the PremierLink control in response to the YI 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 E
• 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 the is no c_dl from the thermostat
except G Pre-cooling is defined as the economizer modulates
to provide 70 F supply all:
When free cooling is available the PremierLink control will
control the compressors, energize the reversing valve(s) and
economizer to provide a supply-air temperature determined to
meet the YI and Y2 calls from the thermostat using the follow-
ing 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)
• YI energized - economizer maintains a SASP =
(SATLOI + 3).
• Y2 energized - economizer maintains a SASP =
(SATLO2 + 3).
Routine 2 (DXCTLO < OAT < 68 F)
• If only YI energized, the economizer maintains a SASP
= (SATLOI + 3).
• If SAT > SASP + 5 and economizer position > 80%,
economizer will go to minimum position for 3 minutes or
until SAT > 68 E
• First stage of mechanical cooling will be energized.
• Integrator resets.
• Economizer opens again and controls to current SASP
after stage one on for 90 seconds.
• With YI and Y2 energized economizer maintains an
SASP = SATLO2 + 3.
• If SAT > SASP + 5 and economizer position >80%,
economizer will go to minimum position for 3 minutes or
until SAT > 68 E
• If compressor one is on then second stage of mechanical
cooling will be energized. Otherwise the first stage will
be energized.
• Integrator resets.
• Economizer opens again and controls to SASP after
stage one on for 90 seconds.
Routine 3 (OAT > 68)
• Economizer is opened 100%.
• Compressors 1 and 2 are cycled based on YI and Y2
using minimum on and off times and watching the sup-
ply air temperature as compared to SATLOI and
SATLO2 set points.
If optional power exhaust is installed, as the outdoor-air
&tmper opens and closes, the power exhaust fans will be ener-
gized and deenergized.
If field-installed accessory CO2 sensors me connected to the
PremierLink TM control, a PID-controlled demand ventilation
strategy will begin to operate. As the CO2 level in the zone
increases above the CO2 set point, the minimum position of the
cktmper will be increased proportionally. As the CO2 level
decreases because of the increase in fresh air, the outdoor-air
&lmper will be proportionally closed.
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