Daikin Skyline OAH003GDAC Installation And Maintenance Manual page 51

10:1 Modulating Furnace
Sequence
Standby Mode
1. Heat enable (Thermostat) open (No call for heat)
2. Line Voltage applied to Terminals L1 & L2
3. 24 VAC is applied to Terminals T2/COM on the SC30-
SM2A (Blue LED lit), to both Ignition Controls (IC) across
terminals 24VAC/GND.
4. The ignition control (IC) performs a self-check routine,
initiates full time flame sensing, flashes the diagnostic
LED for up to four seconds and enters the thermostat
scan standby state (Green LED blinks ½ second ON / ½
second OFF).
Startup/Operation - Call for Heat
1. On call for heat, Thermostat (or heat enable) closes
(Terminals T1/T2 on terminal strip).
2. Provided that the system safety interlocks (circulating
airflow switch and auxiliary high limit) and high limit
contacts are closed, 24 VAC is supplied to Section A IC
terminal TSTAT.
3. Section A ignition control (IC) will check that APS-1
pressure switch contacts are open, [IC terminal APS
(PSW) is not powered].
4. Section A IC Blower (IND) relay contacts close,
powering the Induced Draft Fan (ID Fan) which
operates at high speed.
5. Combustion Air Switch (APS-1 Low) closes powering
terminal APS (PSW) initiating a 15 second pre-purge
period.
6. At end of pre-purge period, main gas valve and spark
igniter are energized to initiate a trial for ignition.
Burners ignite.
7. The SC30-SM2A will output 8.5 VDC to the M Series
modulating valve for a pre-programmed 30 second
warm-up period (Yellow (SU) and Green (AFS) LED's lit)
while maintaining the ID Fan at high speed (Green AFS
LED remains lit) and heater Section A operates at preset
mid-fire input (30% of total heater input).
8. During this warm-up period, the SC30-SM2A ignores the
analog input signal to terminals T12/T13.
9. When the initial timer in SC30-SM2A times out, control
will respond to analog input at terminals T12 and T13.
Green (Mod) LED is lit.
10. If the controller is providing an analog signal between
0.5 and 5.0 VDC to the SC30-SM2A control, only the
modulating section (Section A) will operate from 10%-
50% of total heater input.
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11. For analog inputs from 0.5 to 2.5 VDC, the ID Fan will
run at low speed and LED's PWR (Blue), MOD (Green)
R1 (Red) are lit. (Note: Green (AFS) LED may be lit
if ID Fan pressure is sufficient to close APS-2). The
modulating valve will be powered proportional to the
analog input voltage signal and modulating gas input
from 10 to 30% of total heater input.
12. For analog inputs from 2.6 to 5.0 VDC to SC30-SM2A
the ID Fan will run at high speed (APS-2 closed) and
LED's PWR (Blue), MOD (Green) and AFS (Green) are
lit. The modulating valve will be powered proportional to
the analog input voltage signal and will modulate Section
A gas input from 30 to 50% of total heater input.
13. For analog inputs between 5.2 – 7.5 VDC, the SC30-
SM2A relay R2 is energized closing contacts between
T8 & T9, powering T'stat terminal of Section B Ignition
Control (IC). Section B, IC ID Fan relay contacts close
powering contact APS (PSW) provided APS-3 and
Rollout Switch 2 contacts are closed.
14. Following a 15 second time delay, Section B main gas
valve(s) and spark igniter are energized to initiate a trial
for ignition. Burners ignite. Section B operates at low fire
(25% of total heater input) and ID Fan remains in high
speed. LED's PWR (Blue), MOD (Green) R2 (Red) and
AFS (Green) are lit.
15. For analog inputs less than 7.6 VDC, Modulating Section
A input will be reduced proportional to the analog input
voltage signal and will modulate gas input from 25 to
50% of total heater input.
16. For analog inputs between 7.7 – 10.0 VDC, the SC30-
SM2A relay R3 is energized closing contacts between
T10 & T11, powering Section B 2nd stage gas valve.
Section B operates at high fire (50% of total heater
input) and ID Fan remains in high speed. LED's PWR
(Blue), MOD (Green) R2 (Red), R3 (Red) and AFS
(Green) are lit.
17. For analog inputs less than 9.9 VDC, Modulating Section
A input will be reduced proportional to the analog input
voltage signal and will modulate the gas input from 25 to
50% of total heater input.
18. At an analog input 10.0 VDC, both Section A and Section
B will operate at maximum input.
19. During heater operation, the thermostat, pressure
switches and main burner flame of both sections are
constantly monitored by their IC's and SC30-SM2A to
assure proper system operation.
20. Section B operation continues to operate at high fire
until the analog input signal to the SC30SM2A control
drops below 7.4 VDC. At this point the SC30SM-2A R3
relay opens (Red R3 LED OFF). Section B will operate
at low fire.
21. Modulation will continue on the modulating Section A for
analog input voltages from 7.4 to 4.9 VDC.
51 IM 777-18 • SKYLINE OUTDOOR AIR HANDLER
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