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Cooling —

To start unit, turn on main power supply. Set

system selector switch at COOL position and fan switch at
AUTO position. Adjust thermostat to a setting below room
temperature. Compressor starts on closure of contactor.

Check unit charge. Refer to Refrigerant Charge section on

page 30.

Reset thermostat at a position above room temperature.

Compressor will shut off.
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
exceeds 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) —

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 elec-
tric 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
located between terminals on the switch.
TO SHUT OFF UNIT — Set system selector switch at OFF
position. Resetting heating selector lever below room tem-
perature temporarily shuts unit off until space temperature
falls below 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 sys-

tem selector switches at ON and OFF positions, respec-
tively. 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 en-
ergized. 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
condenser-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 ener-
gized and compressor 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 en-
ergized. On units equipped for 2 stages of heat, when ad-
ditional heat is needed, HC2 is energized through W2.
COOLING, UNITS WITH DURABLADE ECONOMIZER
— When the outdoor-air temperature is above the OAT set-
ting and the room thermostat calls for cooling, the compres-
sor contactor no. 1 is energized to start compressor no. 1 and
outdoor (condenser) fan motor. 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 com-
pressor no. 2. After the thermostat is satisfied and the IFM

is deenergized, the damper moves to the fully closed
position.

When the outdoor-air temperature is below the OAT set-

ting and the thermostat calls for Y1 and G, the economizer
damper moves to the minimum position when the indoor
(evaporator) fan starts. The first stage of cooling is provided
by the economizer. 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 tempera-
ture 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 require-

ments of the conditioned space, economizer cooling is in-
tegrated with mechanical cooling, providing second stage
cooling. Compressor no. 1 and condenser fans will be en-
ergized, 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 com-

pressor and condenser-fan motor will be deenergized. The
damper position 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
— When the outdoor air is above the enthalpy control set-
ting, and the room thermostat calls for cooling, the compres-
sor contactor no. 1 is energized to start compressor no. 1 and
the condenser-fan motors. The evaporator-fan motor is en-
ergized and the economizer damper moves to the minimum
position. Upon further call for cooling, compressor contac-
tor 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 is below the enthalpy control 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 can-
not satisfy the cooling requirements, economizer cooling is
integrated with mechanical cooling and the second compres-
sor is locked out. When the room thermostat is satisfied, the
damper will spring return to the fully closed position.
HEATING, UNITS WITH ECONOMIZER (If Accessory
Heater is Installed) — When the room thermostat calls for
heat through terminal W1, the evaporator-fan contactor and
heater contactor no. 1 are energized. On units equipped for
2 stages of heat, when additional heat is needed, heater
contactor no. 2 is energized through W2. The evaporator-
fan motor is energized, and the economizer damper moves
to the minimum position. If the two-position damper is used,
the outdoor-air damper opens to the minimum position
whenever the evaporator fan opens. When the thermostat is
satisfied, the damper moves to the fully closed position.