57
Operating sequence for 48HJ004-007 units
Cooling, units without economizer —
When thermo-
stat calls for cooling, terminals G and Y1 and the compres-
sor contactor (C) are energized. The indoor (evaporator)
fan motor (IFM), compressor, and outdoor (condenser) fan
motor (OFM) start. The OFM runs continuously while the
unit is in cooling. When the thermostat is satisfied, C is
deenergized and the compressor and OFM shut off. After a
30-second delay, the IFM shuts off. If the thermostat fan
selector switch is in the ON position, the evaporator motor
will run continuously.
Cooling, units with Durablade economizer —
When
the outdoor-air temperature is above the outdoor-air tem-
perature (OAT) setting and the room thermostat calls for
cooling, the compressor contactor is energized to start the
compressor and outdoor (condenser) fan motor (OFM).
The indoor (evaporator) fan motor (IFM) is energized and
the economizer damper moves to the minimum position.
After the thermostat is satisfied, the damper moves to the
fully closed position when IFM is deenergized.
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 evapo-
rator 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
temperature 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 ter-
minal 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 re-
quirements of the conditioned space, economizer cooling
is integrated with mechanical cooling, providing second
stage cooling. The compressor and condenser fan will be
energized and the position of the economizer damper will
be determined by the supply-air temperature.
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 IFM shuts
off after a 30-second delay. The damper then moves to
fully closed position.
Cooling, units with EconoMi$er
When the outdoor-air temperature (OAT) is above the
ECON SP set point and the room thermostat calls for
Stage 1 cooling (R to G + Y1), the indoor (evaporator) fan
motor (IFM) is energized and the EconoMi$er damper
modulates to minimum position. The compressor contac-
tor is energized to start the compressor and outdoor (con-
denser) fan motor (OFM). 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$er inte-
grates free cooling with mechanical cooling. This is accom-
plished by the strategies below.
NOTE: Compressor has a two minute Minimum On, Mini-
mum Off, and Interstage delay timer.
1. If Y1 is energized, and the room thermostat calls for
Y2 (2-stage) thermostat), the compressor and OFM
are energized. The position of the EconoMi$er
damper is maintained at its current value.
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
position of the EconoMi$er damper is maintained at
its current value.
3. If Y1 is energized, and the compressor is already
energized (see Step 2) and the room thermostat calls
for Y2, the compressor continues to operate.
4. If the compressor is energized and the thermostat is
satisfied, the compressor, OFM, and IFM are deener-
gized and the EconoMi$er modulates closed.
When the OAT is below the MECH CLG LOCKOUT set
point, the compressors remain off.
Heating, units without economizer —
When the ther-
mostat calls for heating, terminal W1 is energized. The
induced-draft motor is 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 additional heat is
needed, W2 is energized and the high-fire solenoid on the
main gas valve (MGV) is energized. When the thermostat is
satisfied and W1 is deenergized, the IFM stops after a
45-second time-off delay.
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