58
Heating, units with economizer/two-position
damper —
When the thermostat calls for heating, termi-
nal W1 is energized. The induced-draft motor is energized
and the burner ignition sequence begins. The indoor (evap-
orator) fan motor (IFM) is energized 45 seconds after a
flame is ignited and the damper moves to the minimum po-
sition. If the accessory two-position damper is used, the
outdoor-air damper opens to the minimum position when-
ever the evaporator fan runs. On units equipped for two
stages of heat, when additional heat is needed, W2 is ener-
gized 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. The economizer damper then moves to the fully
closed position. When using continuous fan, the damper
will remain in the minimum position.
Operating sequence for 48HJ008-014 units
Cooling, units without economizer —
When thermo-
stat calls for cooling, terminals G and Y1 are energized.
The indoor (evaporator) fan contactor (IFC) and compres-
sor contactor no. 1 (C1) are energized, and evaporator-fan
motor, compressor no. 1, and condenser fans start. The
condenser-fan motors run continuously while unit is cool-
ing. For units with 2 stages of cooling, if the thermostat
calls for a second stage of cooling by energizing Y2, com-
pressor contactor no. 2 (C2) is energized and compressor
no. 2 starts.
When the thermostat is satisfied, C1 and C2 are deener-
gized and the compressors and outdoor (condenser) fan
motors (OFM) shut off. After a 30-second delay, the indoor
(evaporator) fan motor (IFM) shuts off. If the thermostat fan
selector switch is in the ON position, the evaporator mo-
tors will run continuously.
Cooling, units with Durablade economizer —
When
the outdoor-air temperature is above the OAT setting and
the room thermostat calls for cooling, the compressor con-
tactor no. 1 is energized to start compressor no. 1 and out-
door (condenser) fan motors (OFM). The indoor (evapora-
tor) 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 ener-
gized, starting compressor 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 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. Compressor no. 1 and 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 com-
pressor and condenser 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 IFM shuts
off after a 30-second delay. The damper then moves to ful-
ly 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$er inte-
grates free cooling with mechanical cooling. This is accom-
plished by the strategies below.
NOTE: Compressor has a two minute Minimum On, Mini-
mum Off, and Interstage delay timer.
1. If Y1 is energized, and the room thermostat calls for
Y2 (2-stage thermostat), compressor no. 1 and OFM
are energized. The position of the EconoMi$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), compressor no. 1 and OFM are energized.
Controls (cont)
