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OPERATING SEQUENCE
COOLING, UNITS WITHOUT ECONOMIZER — When thermo-
stat calls for cooling, terminals G and Y1 are energized. The in-
door (evaporator) fan contactor (IFC) and compressor contactor
no. 1 (C1) are energized and evaporator-fan motor, compressor
no. 1 (036-150 and 216-300) or unloaded compressor (180),
and condenser fan(s) start. The condenser-fan motor runs con-
tinuously while unit is cooling. On 090-300 units, if the thermo-
stat calls for a second stage of cooling by energizing Y2,
compressor contactor no. 2 (C2) is energized and compressor
no. 2 starts (090-150 and 216-300), or compressor no. 1 runs
fully loaded (180).
HEATING, UNITS WITHOUT ECONOMIZER (IF ACCESSORY
OR OPTIONAL HEATER IS INSTALLED) — Upon a call for
heating through terminal W1, IFC and heater contactor no. 1
(HC1) are energized. On units equipped for 2 stages of heat,
when additional heat is needed, HC2 is energized through W2.
COOLING, UNITS WITH DURABLADE ECONOMIZER (036-
150) — When the outdoor-air temperature is above the outdoor-
air thermostat (OAT) setting and the room thermostat calls for
cooling, compressor contactor no. 1 is energized to start com-
pressor no. 1 and the condenser-fan motor. The evaporator-fan
motor 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. Af-
ter the thermostat is satisfied, the damper moves to the fully-
closed position.
When the outdoor-air temperature is below the OAT setting and
the thermostat calls for cooling, the economizer dampers move
to the minimum position. If the supply-air temperature is above
57 F, the damper continues to open until it reaches the fully-
openpositionoruntilthesupply-airtemperaturedropsbelow57F.
When the supply-air temperature falls to between 57 F and 52 F,
the damper will remain at an intermediate open position. If the
supply-air temperature falls below 52 F, the damper will modu-
late closed until it reaches the minimum position or until the
supply-air temperature is above 52 F. When the thermostat is
satisfied, the damper will move to the fully-closed 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. Compres-
sor no. 1 and the condenser fan will be energized and the
position of the economizer damper will be determined by the
supply-air temperature. Compressor no. 2 is locked out.
When the second stage of cooling is satisfied, the compressor
and condenser-fan motor will be deenergized. The damper po-
sition will be determined by the supply-air temperature.
When the first stage of cooling is satisfied, the damper will move
to fully-closed position.
COOLING, UNITS WITH PARABLADE ECONOMIZER
(036-072) — When the outdoor air is above the enthalpy control
(EC) setting, and the room thermostat calls for cooling, the com-
pressor contactor is energized to start the compressor and the
condenser-fan motor. The evaporator-fan motor is energized
and the economizer damper moves to the minimum position. Af-
ter the room thermostat is satisfied, the damper will spring re-
turn to the fully-closed position.
When the outdoor-air is below the EC setting and the thermostat
calls for cooling, the economizer outdoor-air damper is opened
proportionally to maintain between 50 and 56 F at the mixed-air
sensor. If outdoor air alone cannot satisfy the cooling require-
ments, economizer cooling is integrated with mechanical cool-
ing. When the room thermostat is satisfied, the damper will
spring return to the fully-closed position.
COOLING, UNITS WITH PARABLADE ECONOMIZER
(090-150) — When the outdoor-air is above the enthalpy control
(EC) setting, and the room thermostat calls for cooling, com-
pressor contactor no. 1 is energized to start compressor
no. 1 and the condenser-fan motor. The evaporator-fan motor is
energized and the economizer damper moves to the minimum
position. Upon a further call for cooling, compressor contactor
no. 2 is energized, starting compressor no. 2. After the room
thermostat is satisfied, the damper will spring return to the fully-
closed position.
When the outdoor-air temperature is below the EC setting and
the thermostat calls for cooling, the economizer outdoor-air
damper is opened proportionally to maintain between 50 and
56 F at the mixed-air sensor. If outdoor-air alone cannot satisfy
the cooling requirements, economizer cooling is integrated with
mechanical cooling, and the second compressor is locked out.
When the room thermostat is satisfied, the damper will spring
return to the fully-closed position.
COOLING, UNITS WITH ECONOMIZER (180-300) — Upon a
call for cooling, when outdoor ambient temperature is above the
temperature control setting, the evaporator and condenser fans
and compressor energize. The economizer damper moves to
VENT position.
Upon a first-stage call for cooling, when outdoor ambient tem-
perature is below the temperature control setting, the evapora-
tor fan starts and economizer damper modulates to maintain
mixed-air temperature. The compressor(s) remains off.
Upon a second-stage call for cooling, compressor no. 1 (180-
300) or unloaded compressor (180) is energized and mechani-
cal cooling is integrated with economizer cooling. Compressor
no. 2 is locked out. If the air temperature is above 50 F, a cooling
lockout switch prevents the compressor(s) from running.
When supply-air temperature drops below a fixed set point, the
economizer damper modulates to maintain the temperature at
the fixed set point.
A freeze protection thermostat (FPT) is located on the evapora-
tor coil. It detects frost build-up and turns off the compressor, al-
lowing the coil to clear. Once frost has melted, the compressor
can be reenergized.
HEATING, UNITS WITH ECONOMIZER (036-150) (IFACCES-
SORY OR OPTIONAL HEATER IS INSTALLED) — When the
room thermostat calls for heat through terminal W1, the
evaporator-fan contactor and heater contactor no. 1 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 during
heating. When the thermostat is satisfied, the damper moves to
the fully closed position.
HEATING, UNITS WITH ECONOMIZER (180-300) (IFACCES-
SORY OR OPTIONAL HEATER IS INSTALLED) — The
outdoor-air damper stays at VENT position while the evaporator
fan is operating. Refer to Heating, Units Without Economizer
section, above, for remainder of operating sequence.
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