Bryant 580D - Manual (Page 63)

CONTROLS
OPERATING SEQUENCE
Cooling, Units Without Economizer — When thermostat calls
for cooling, terminals G and Y1 are energized. The indoor
(evaporator) fan contactor (IFC) and compressor contactor
no. 1 (C1) are energized, and evaporator-fan motor (IFM), com-
pressor no. 1 (580D036-150 and 579F216-300) or unloaded
compressor (579F180), and condenser fan(s) start. The liquid
line solenoid value for compressor no. 1 is deenergized open.
The condenser-fan motor(s) runs 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, compressor con-
tactor no. 2 (C2) is energized and compressor no. 2 starts
(580D090-150 and 579F216-300), or compressor no. 1 runs
fully loaded (579F180). The liquid line solenoid valve for com-
pressor no. 2 (579F180 and 240) is deenergized to open.
Heating, Units Without Economizer (580D036-150) — When
the thermostat calls for heating, terminal W1 is energized. In or-
der 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 (IDM) is then 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.
Heating, Units Without Economizer (579F180-300)
NOTE: The 579F180-300 units have 2 stages of heat.
When the thermostat calls for heating, power is sent to W on the
IGC (integrated gas unit controller) board. An LED (light-
emitting diode) on the IGC board will be on during normal op-
eration. A check is made to ensure that the rollout switch and
limit switch are closed. The induced-draft motor is then ener-
gized, and when speed is proven with the hall effect sensor on
the motor, the ignition activation period begins. The burners will
ignite within 5 seconds.
If the burners do not light, there is a 22-second delay before an-
other 5-second attempt. If the burners still do not light, this se-
quence is repeated for 15 minutes. After the 15 minutes have
elapsed, if the burners still have not lighted, heating is locked
out. To reset the control, break 24-v power to the thermostat.
When ignition occurs the IGC board will continue to monitor the
condition of the rollout and limit switches, the hall effect sensor,
as well as the flame sensor. If the unit is controlled through a
room thermostat set for fan auto., 45 seconds after ignition oc-
curs, the indoor-fan motor will be energized. If for some reason
the overtemperature limit opens prior to the start of the indoor
fan blower, on the next attempt, the 45-second delay will be
shortened to 5 seconds less than the time from initiation of heat
to when the limit tripped. Gas will not be interrupted to the burn-
ers and heating will continue. Once modified, the fan on delay
will not change back to 45 seconds unless power is reset to the
control.
When additional heat is required, W2 closes and initiates power
to the second stage of the main gas valve. When the thermostat
is satisfied, W1 and W2 open and the gas valve closes, inter-
rupting the flow of gas to the main burners. If the call for W1
lasted less than 1 minute, the heating cycle will not terminate
until 1 minute after W1 became active. If the unit is controlled
through a room thermostat set for fan auto., the indoor-fan mo-
tor will continue to operate for an additional 45 seconds then
stop. If the overtemperature limit opens after the indoor motor is
stopped within 10 minutes of W1 becoming inactive, on the next
cycle the time will be extended by 15 seconds. The maximum
delay is 3 minutes. Once modified, the fan off delay will not
change back to 45 seconds unless power is reset to the control.
A LED indicator is provided on the IGC to monitor operation.
The IGC is located by removing the side panel and viewing the
IGC through the view port located in the control box access
panel. During normal operation, the LED is continuously on.
Cooling, Units With Durablade Economizer (580D036-150)
— When the outdoor-air temperature is above the OAT
(outdoor-air thermostat) setting and the room thermostat calls
for cooling, compressor contactor no. 1 is energized to start
compressor no. 1 and the outdoor (condenser) fan motor
(OFM). The indoor (evaporator) 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 energized, starting compressor no. 2 (090-150 only). After
the thermostat is satisfied, the damper moves to the fully closed
position when using an auto fan or to the minimum position
when using a continuous fan.
When the outdoor-air temperature is below the OAT setting 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
when using an auto fan or to the minimum position when using
a continuous fan.
If the outdoor air alone cannot satisfy the cooling requirements
of the conditioned space, economizer cooling is integrated with
mechanical cooling, providing second-stage cooling. Compres-
sor no. 1 and the condenser fan will be energized and the po-
sition 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 compressor
and OFM will be deenergized. The damper position will be de-
termined by the supply-air temperature.
After a 30-second delay, the IFM shuts off. If the thermostat
fan selector switch is in the ON position, the IFM will run
continuously.
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