Bryant 580D - Manual (Page 64)

CONTROLS (cont)
Cooling, Units With Parablade Economizer (580D036-072)
— When the outdoor air is above the enthalpy control (EC) set-
ting, and the room thermostat calls for cooling, and the com-
pressor contactor is energized to start the compressor and the
condenser-fan motor. The evaporator-fan motor is energized
and the economizer damper moves to the minimum position. Af-
ter the room thermostat is satisfied, the damper will spring re-
turn to the fully closed position.
When the outdoor air is below the (EC) setting and the ther-
mostat 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 cannot satisfy the cooling
requirements, economizer cooling is integrated with mechanical
cooling. When the room thermostat is satisfied, the damper will
spring return to the fully closed position.
Cooling, Units With Parablade Economizer (580D090-150)
— When the outdoor air is above the enthalpy control (EC) set-
ting, and the room thermostat calls for cooling, and compressor
contactor no. 1 is energized to start compressor no. 1 and the
condenser-fan motor. The evaporator-fan motor is energized
and the economizer damper moves to the minimum position.
Upon a further call for cooling, compressor contactor no. 2 is en-
ergized, starting compressor no. 2. After the room thermostat
is satisfied, the damper will spring return to the fully closed
position.
When the outdoor-air temperature is below the EC 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 cannot satisfy
the cooling requirements, economizer cooling is integrated with
mechanical cooling, and the second compressor is locked out.
When the room thermostat is satisfied, the damper will spring
return to the fully closed position.
Cooling, Units With Economizer (579F180-300) — Upon a
call for cooling, when outdoor ambient is above the temperature
control setting, the economizer damper moves to VENT posi-
tion. The compressors and evaporator and condenser fans
energize.
Upon a first call for cooling, when outdoor ambient is below the
temperature control setting, the evaporator fan starts and the
economizer opens to maintain 53 F leaving-air temperature.
The compressors remain off.
Upon a second-stage call for cooling, compressor no. 1 is en-
ergized and mechanical cooling is integrated with econo-
mizer cooling. If the outdoor-air temperature drops below
50 F, a cooling lockout switch prevents the compressors from
running.
When supply-air temperature drops below a fixed set point, the
economizer damper modulates to maintain the temperature at
the fixed set point.
A freeze protection thermostat (FPT) is located on the evapora-
tor coil. It detects frost build-up and turns off the compressors,
allowing the coil to clear. Once frost has melted, the compres-
sors can be reenergized.
Heating, Units With Economizer (580D036-150) — When the
thermostat calls for heating, terminal W1 is energized. In order
to prevent thermostat short-cycling, the unit is locked into the
Heating mode for at least 1 minute when W1 is energized. The
induced-draft motor is then energized and the burner ignition
sequence begins. The indoor (evaporator) fan motor (IFM) is
energized 45 seconds after a flame is ignited and the damper
moves to the minimum position. 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 en-
ergized. When the thermostat is satisfied and W1 is deener-
gized, 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 mini-
mum position.
Heating, Units With Economizer (579F180-300) — Outdoor-
air damper stays at VENT position while evaporator fan is op-
erating. Refer to Heating, units without economizer section on
page 63 for remainder of operating sequence.
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