Bryant 559F - Manual (Page 3)

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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), compressor no. 1 and condenser
fan(s) start. The condenser-fan motor(s) runs continuously
while unit is cooling. When the thermostat calls for a second
stage of cooling by energizing Y2, compressor contactor no. 2
(C2) is energized and compressor no. 2 starts.
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 operation. A check is made to ensure that the rollout
switch and limit switch are closed. The induced-draft motor
is then energized, 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
another 5-second attempt. If the burners still do not light,
this sequence is repeated for 15 minutes. After the 15 min-
utes have elapsed, if the burners still have not lighted, heat-
ing is locked out. To reset the control, break 24-v power to
the thermostat.
When ignition occurs the IGC board will continue to moni-
tor the condition of the rollout and limit switches, the hall
effect sensor, as well as the flame sensor. If the unit is con-
trolled through a room thermostat set for fan auto., 45 sec-
onds after ignition occurs, 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 burners and heat-
ing 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, interrupting 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 motor 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.
An LED indicator is provided on the IGC to monitor opera-
tion. 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 con-
tinuously on.
Heating, Units Without Economizer (559F180-300, If Acces-
sory or Optional Heater is Installed)
Upon a call for heating through terminal W1, IFC and
heater contactor no. 1 (HC1) are energized. On units
equipped for 2 stages of heat, when additional heat is
needed, HC2 is energized through W2.
Cooling, Units With Economizer
Upon a call for cooling, when outdoor ambient is above the
temperature control setting, the economizer damper moves
to VENT position. The compressors and evaporator and con-
denser 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 tem-
perature. The compressors remain off.
Upon a second-stage call for cooling, compressor no. 1 is
energized 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 tempera-
ture at the fixed set point.
Freeze protection thermostats (FPT) are located on the evap-
orator coil. They detect frost build-up and turn the compres-
sors off locking them out and requiring a manual reset. Once
frost has melted, the compressors can be reenergized.
Heating, Units With Economizer
Outdoor-air damper stays at VENT position while evap-
orator fan is operating. Refer to Heating, Units Without
Economizer (579F180-300) and Heating, Units Without
Economizer (559F180-300, If Accessory or Optional Heater is
Installed) sections on this page for remainder of operating
sequence.