Controls; Operating Sequence; Heating, Units Without Economizer; Cooling, Units With Durablade Economizer - Carrier 50TFQ004 Product Data

Controls

Operating sequence

Cooling, units without economizer — When thermo-
stat calls for cooling, terminals G and Y1 are energized.
The indoor fan contactor (IFC), reversing valve solenoid
(RVS1) and compressor contactor no. 1 (C1) are energized
and indoor-fan motor, compressor no. 1, and outdoor fans
start. The outdoor-fan motor(s) run continuously while unit
is cooling. On 50TJQ008-012 units, if the thermostat calls
for a second stage of cooling by energizing Y2, compres-
sor contactor no. 2 (C2) and reversing valve solenoid
(RVS2) are energized and compressor no. 2 starts.
Heating, units without economizer (50TFQ004-
007) — Set system switch at AUTO. or HEAT position.
Set thermostat at desired temperature.
When the thermostat calls for heat, the IFC, outdoor-fan
contactor (OFC), and compressor contactor are energized.
The RVS is deenergized and switches position, and the in-
door fan, outdoor fan, and compressor are energized.
If the thermostat calls for a second stage of heat, the
heater contactor (HC) is energized and starts the electric
heaters.
When the space temperature approaches the heating
temperature set point, heating stages cycle off. The revers-
ing valve solenoid is reenergized.
Heating, units without economizer (50TFQ008-
012) — Upon a request for heating from the space ther-
mostat, terminal W1 will be energized with 24 v. The IFC,
outdoor-fan contactor (OFC), C1, and C2 will be ener-
gized. The reversing valves switch position and the indoor
fan, outdoor fan, compressor no. 1, and compressor no. 2
are energized.
If the space temperature continues to fall while W1 is en-
ergized, W2 will be energized with 24 v, and the heater
contactor(s) (HC) will be energized, which will energize the
electric heater(s).
When the space thermostat is satisfied, W2 will be deen-
ergized first, and the electric heater(s) will be deenergized.
Upon a further rise in space temperature, W1 will be
deenergized, and the reversing valve solenoids (RVS1 and
RVS2) will be energized.
Cooling, units with Durablade economizer — When
the outdoor-air temperature is above the outdoor-air ther-
mostat (OAT) setting and the room thermostat calls for
cooling, compressor contactor no. 1 is energized to start
compressor no. 1 and the outdoor-fan motor(s). RVS1 (re-
versing valve solenoid) is energized. The indoor-fan motor
is energized and the economizer damper moves to the
minimum position. Upon a further call for cooling, com-
pressor contactor no. 2 will be energized (50TFQ008-
012), starting compressor no. 2. RVS2 is energized. After
the thermostat is satisfied, the damper moves to the fully
closed position.
When the outdoor-air temperature is below the OAT set-
ting 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 open position or until the supply-
air temperature drops below 52 F.
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 modulate 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 re-
quirements of the conditioned space, economizer cooling
is integrated with mechanical cooling, providing second-
stage cooling. Compressor no. 1 and the outdoor fan will
be energized and the position of the economizer damper
will be determined by the supply-air temperature. Com-
pressor no. 2 (50TFQ008-012) is locked out.
When the second stage of cooling is satisfied, the com-
pressor, RVS2, and outdoor-fan motor(s) will be deener-
gized. 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 EconoMi$er (50TFQ004-007)
— When the outdoor-air temperature (OAT) is above the
ECON SP set point and the room thermostat calls for
Stage 1 cooling (R to G + Y1), the indoor-fan motor (IFM)
is energized and the EconoMi$er damper modulates to
minimum position. The compressor contactor is energized
to start the compressor and outdoor-fan motor (OFM) and
RVS1 (reversing valve solenoid). After the thermostat is
satisfied, the damper modulates to the fully closed position
when the IFM is deenergized.
When the OAT is below the ECON SP setting and the
room thermostat calls for Stage 1 cooling (R to G + Y1),
the EconoMi$er modulates to the minimum position when
the IFM is energized. The EconoMi$er provides Stage 1 of
cooling by modulating the return and outdoor-air dampers
to maintain a 55 F supply air set point. If the supply-air
temperature (SAT) is greater than 57 F, the EconoMi$er
modulates open, allowing a greater amount of outdoor air
to enter the unit. If the SAT drops below 53 F, the outdoor
air damper modulates closed to reduce the amount of out-
door air. When the SAT is between 53 and 57 F, the
EconoMi$er maintains its position.
If outdoor-air alone cannot satisfy the cooling require-
ments of the conditioned space, and the OAT is above the
MECH CLG LOCKOUT set point, the EconoMi$er inte-
grates free cooling with mechanical cooling. This is accom-
plished by the strategies below.
NOTE: Compressor has a 2-minute Minimum On, Mini-
mum Off, and Interstage delay timer.
1. If Y1 is energized, and the room thermostat calls for
Y2 (2-stage thermostat), the compressor and OFM
are energized. The EconoMi$er damper is main-
tained at its current position.
2. If Y1 is energized for more than 20 minutes, and Y2
is not energized (whether or not a 2-stage thermostat
is used), the compressor and OFM are energized.
The EconoMi$er damper is maintained at its current
position.
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