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Operating Sequence
COOLING, UNITS WITHOUT ECONOMIZER — When
thermostat calls for cooling, terminals G and Y1 are energized.
The indoor (evaporator) fan contactor (IFC), compressor con-
tactor no. 1 (C1) and outdoor-fan contactor (OFC) are ener-
gized, and evaporator-fan motor, compressor no. 1, and both
condenser fans start. The condenser-fan motors run continuous-
ly 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.
When the thermostat is satisfied, C1 and C2 are deener-
gized and the compressors and outdoor (condenser) fan motors
(OFM) shut off. After a 30-second delay, the indoor (evapora-
tor) fan motor (IFM) shuts off. If the thermostat fan selector
switch is in the ON position, the evaporator-fan motor will run
continuously.
HEATING, UNITS WITHOUT ECONOMIZER — When
the thermostat calls for heating, terminal W1 is energized. In
order to prevent thermostat short-cycling, the unit is locked
into the Heating mode for at least 1 minute when W1 is ener-
gized. The induced-draft motor (IDM) is then energized and
the burner ignition sequence begins. The indoor (evaporator)
fan motor (IFM) is energized 45 seconds after a flame is
ignited. On units equipped for two stages of heat, when addi-
tional heat is needed, W2 is energized and the high-fire sole-
noid on the main gas valve (MGV) is energized. When the
thermostat is satisfied and W1 and W2 are deenergized, the
IFM stops after a 45-second time-off delay.
COOLING, UNITS WITH ECONOMI$ERIV — When free
cooling is not available, the compressors will be controlled by
the zone thermostat. When free cooling is available, the
outdoor-air damper is modulated by the EconoMi$erIV 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 F,
the dampers will be modulated (open or close) to bring the
supply-air temperature back within the set point limits.
For EconoMi$erIV operation, there must be a thermostat
call for the fan (G). This will move the damper to its minimum
position during the occupied mode.
Above 50 F supply-air temperature, the dampers will modu-
late from 100% open to the minimum open position. From 50 F
to 45 F supply-air temperature, the dampers will maintain
at the minimum open position. Below 45 F the dampers will
be completely shut. As the supply-air temperature rises, the
dampers will come back open to the minimum open position
once the supply-air temperature rises to 48 F.
If optional power exhaust is installed, as the outdoor-air
damper opens and closes, the power exhaust fans will be ener-
gized and deenergized.
If field-installed accessory CO
2
sensors are connected to the
EconoMi$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$ERIV — When the
room thermostat calls for heat, the heating controls are ener-
gized as described in the Heating, Units Without Economizer
section. When the indoor fan is energized, the economizer
damper moves to the minimum position. When the indoor fan
is off, the economizer damper is fully closed.
COOLING, UNITS WITH ECONOMI$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 the 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 =
(SATLO1 + 3).
• Y2 energized – economizer maintains a SASP =
(SATLO2 + 3).
Routine 2 (DXCTLO < OAT < 68 F)
• If only Y1 energized, the economizer maintains a SASP
=(SATLO1+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.
• Economizer opens again and controls to current SASP
after stage one on for 90 seconds.
• With Y1 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 F.
• 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.