21
Heating —
To start unit, turn on main power supply.
Set thermostat at HEAT position at a setting above room
temperature, fan at AUTO position.
First stage of thermostat energizes the indoor fan motor,
compressor, and outdoor fan; second stage energizes electric
heater elements, if installed. Check heating effects at air supply
grille(s).
If accessory electric heaters do not energize, reset limit
switch (located on indoor-fan scroll) by depressing 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 at the suction line at
the loss-of-charge/low-pressure 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. In-
door 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 energized.
The indoor-fan contactor (IFC), RVS1 (reversing valve sole-
noid), and compressor contactor no. 1 (C1) are energized and
the indoor-fan motor, compressor no. 1, outdoor fan contactor
(OFC), and outdoor fans start. The outdoor-fan motors run con-
tinuously while unit is cooling. If the thermostat calls for a sec-
ond stage of cooling by energizing Y2, compressor contactor
no. 2 (C2) and RVS2 are energized and compressor no. 2 starts.
HEATING, UNITS WITHOUT ECONOMIZER — Upon a
call for heating through terminal W1, G, IFC, OFC, C1, and C2
are energized. On units equipped for 2 stages of heat, when ad-
ditional heat is needed, HC is energized through W2.
COOLING, UNITS WITH DURABLADE ECONO-
MIZER — When the outdoor-air temperature is above the
OAT setting and the room thermostat calls for cooling, the
compressor contactor no. 1 is energized to start compressor
no. 1 and outdoor fan motors. RVS1 (reversing valve solenoid)
is energized). The indoor-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 en-
ergized, starting compressor no. 2. RVS2 is energized. 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 setting
and the thermostat calls for Y1 and G, the economizer damper
moves to the minimum position when the indoor fan starts. The
first stage of cooling is provided by the economizer. If the
supply-air temperature is above 14 C (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 modu-
late open until the supply-air temperature falls below 13 C
(55 F) or the damper reaches the fully open position.
When the supply-air temperature is between 13 C (55 F)
and 11 C (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 11 C (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
13 C (55 F) or the damper reaches the minimum position.
When the supply-air temperature is between 13 C (55 F)
and 14 C (57 F), the supply-air thermostat has open switches
between the T2 and 24 vac terminals. This causes the econo-
mizer 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 integrat-
ed with mechanical cooling, providing second stage cooling.
Compressor no. 1 and outdoor fans 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 compres-
sor, RVS2, and outdoor-fan motors 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.
HEATING, UNITS WITH DURABLADE ECONO-
MIZER — Upon a request for heating from the space thermo-
stat, terminal W1 will be energized with 24 v. The IFC, OFC,
C1, and C2 will be energized. The reversing valves switch po-
sition and the indoor fan, outdoor fan, compressor no. 1, and
compressor no. 2 are energized. The economizer damper
moves to the minimum position.
If the space temperature continues to fall while W1 is ener-
gized, W2 will be energized with 24 v, and the heater contac-
tor(s) (HC) will be energized, which will energize the electric
heaters.
When the thermostat is satisfied, the damper moves to the
fully closed position.
DEFROST — When the temperature of the outdoor coil drops
below –2 C (28 F) as sensed by the defrost thermostat (DFT2)
and the defrost timer is at the end of a timed period (adjustable
at 30, 50, or 90 minutes), reversing valve solenoids (RVS1 and
RVS2) are energized and the OFC is deenergized. This switch-
es the position of the reversing valves and shuts off the outdoor
fans. The electric heaters (if installed) will be energized.
The unit continues to defrost until the coil temperature as
measured by the DFT2 reaches 18 C (65 F), or the duration of
defrost cycle completes a 10-minute period.
During the Defrost mode, if circuit 1 defrosts first, RVS1
will oscillate between Heating and Cooling modes until the
Defrost mode is complete.
At the end of the defrost cycle, the electric heaters (if in-
stalled) will be deenergized; the reversing valves switch and
the outdoor-fan motors will be energized. The unit will now
operate in the Heating mode.
If the space thermostat is satisfied during a defrost cycle, the
unit will continue in the Defrost mode until the time or temper-
ature constraints are satisfied.
