80
IM 738-2
Wiring Diagrams
Figure 82. Super Mod gas furnace control (1000 MBH), continued
OVER 1/2 P.S.I.
SHUTOFF
SHUTOFF
PIPING DIAGRAM
(THRU 1/2 P.S.I.)
TEST
CONN.
TEST
COCK
SWITCH
AIR
BURNER
BLOWER
MODULATING
ACTUATOR
V
V
COCK
GV1B
REG.
HIGH PRESS.
VALVE AND
PRESS. REG.
--MAIN
COMBINATION GAS CONTROLS
GV1A
VALVE AND
--FIRST
MANUAL VALVE.
GV4B
GV4A
(TYPICAL)
COCK
GV5B
GV5A
IGNITION PERIOD TERMINAL #10 (IGNITION TRANSFORMER--IT) WILL BE DE-ENERGIZED AND TERMINAL #9 (RELAY R23 COIL AND MAIN GAS VALVE
S--GV4 & GV5) WILL BE ENERGIZED
PREPURGE PERIOD WILL BEGIN.
BLOWER MOTOR (BM). WHENEVER POWER IS RESTORED TO THE FLAME SAFEGUARD, THE FLAME SAFEGUARD WILL GO THROUGH A 10 SECOND INITIAT
ION PERIOD BEFORE THE
CONTROL (FLC) AND TERMINAL #6 ON THE FLAME SAFEQUARD (FSG) IS POWERED. THE FLAME SAFEGUARD THEN ENERGIZES ITS TERMINAL #4, WHIC
H POWERS THE BURNER COMBUSTION AIR
SAFEGUARD (FSG). UPON A CALL FOR HEAT, THE CONTROL SYSTEM WILL CLOSE (BO#11) ON THE MAIN CTRL BRD (MCB), THUS ENERGIZING RELAY
(R20).
AT ITS PRESENT POSITION. THE HEATING CAPACITY IS MONITORED BY THE MAIN CTRL BRD (MCB) THROUGH (AI#10) VIA A POSITION FEEDBACK
POTENTIOMETER ON THE ACTUATOR.
AND THE CONTROL SYSTEM WILL BE ALLOWED TO CONTROL THE FIRING RATE. THE FLAME SAFEGUARD CONTAINS "LEDS"(LOWER LEFT CORNER) THAT
WILL GLOW TO INDICATED OPERATION.
(LS1) WILL BE 'MADE'. IF (LS1) IS NOT 'MADE' THE COMBINATION GAS CONTROL START VALVES (GV1) WILL NOT OPEN AND THE BURNER WILL
GO OUT ON SAFETY LOCKOUT.
N/C CONTACT OF (R23). AT THE COMPLETION OF THE 60 SECOND PREPURGE CYCLE THE VALVE WILL BE AT THE MINIMUM OPEN POSITION AND THE
MINIMUM POSITION SWITCH
AIR SWITCH (AS). THIS INITIATES THE 60 SECOND PREPURGE CYCLE. CONCURRENTLY, (LS2) POWERS TIMER (TD10) WHICH WILL ENERGIZE REL
AY (R21) AFTER 20 SECONDS.
POSITION FOR PREPURGE. WHEN THE AIR CONTROL VALVE REACHES THE FULL OPEN POSITION SWITCH (LS2) IS 'MADE', POWERING (FSG) TERMIN
AL #7 THROUGH THE BURNER
FOR A NEW CALL FOR HEAT, (VM1) THROUGH THE N/O CONTACTS OF (R20) AND THE N/C CONTACTS OF (R21), WILL RE-POSITION THE BURNER AIR
VALVE TO ITS MAXIMUM OPEN
TERMINAL #10 (IGNTION TRANSFORMER--IT) WILL BE ENERGIZED. IF FLAME IS BEING DETECTED THROUGHT THE FLAME ROD (FD) AT THE COMPLE
TION OF THE 10 SECOND TRIAL FOR
AFTER COMPLETION OF THE 60 SECOND PREPURGE PERIOD THERE WILL BE A 10 SECOND TRIAL FOR IGINITION DURING WHICH TERMINAL #8 (COMBI
NATION GAS VALVE--GV1) AND
THE ACTUATOR WILL RE-POSITION TOWARD A LOWER FIRING RATE. IF NEITHER (BO#9) OR (BO#10) ON THE MAIN CONTROL BOARD (MCB) ARE CLO
SED, THE ACTUATOR WILL REMAIN
WILL RE-POSITION TOWARD A HIGHER FIRING RATE UNTIL (BO#10) OPENS OR THE ACTUATOR REACHES ITS MAXIMUM POSITION. WHEN THE MAIN
CONTROL SYSTEM CLOSES (BO#9),
THE BURNER AIR AND GAS VALVES FOR THE REQUIRED FIRING RATE. WHEN THE MAIN CONTROL SYSTEM CLOSES (BO#10) ON THE MAIN CTRL BRD (
MCB), THE GAS VALVE ACTUATOR
AFTER THE FLAME HAS LIT AND BEEN PROVEN, RELAY (R23) IS ENERGIZED ALLOWING (VM1), AS CONTROLLED BY (BO#9) & (BO#10) ON THE MAIN
CTRL BRD (MCB), TO POSITION
WHEN THE ROOFTOP UNIT IS ENERGIZED 120 VOLT POWER IS SUPPLIED TO THE SYSTEM ON-OFF SWITCH (S1), TO BURNER ON-OFF SWITCH (S3) AN
D 24 VOLTS TO THE (BO#11)
INPUT #5 ON THE MICROTECH II MAIN CONTROL BOARD (MCB).
POWER IS FURNISHED THROUGH THE SYSTEM ON-OFF SWITCH (S1), THROUGH THE BURNER ON-OFF SWITCH (S3), THROUGH RELAY (R20 CONTACTS, T
HROUGH THE HIGH LIMIT
WHEN 120 VOLT
CONTACTS ON THE MAIN CTRL BRD (MCB). BURNER ON-OFF SWITCH (S3) WILL POWER THE MODULATING GAS VALVE ACTUATOR (VM1) AND TERMINAL
#5(L1) ON THE FLAME
TERMINAL #3 WILL ENERGIZE THE HEAT ALARM RELAY (R24), WHICH WOULD THEN ENERGIZE THE REMOTE 'HEAT FAIL' INDICATOR LIGHT AND SEND
A FAIL SIGNAL TO BINARY
THUS DE-ENERGIZING THE BURNER AND TERMINAL #3 WILL BECOME ENERGIZED. THE FLAME SAFEGUARD WOULD THEN BE ON SAFETY LOCKOUT AND W
OULD REQUIRE MANUAL RESETTING.
IN THE EVENT THE FLAME FAILS TO IGNITE OR THE FLAME SAFEGUARD FAILS TO DETECT ITS FLAME WITHIN 10 SECONDS, TERMINALS #4, 8, 9,
AND 10 WILL BE DE-ENERGIZED,
WHEN (R21) IS ENERGIZED (VM1) WILL START THE AIR CONTROL VALVE ON ITS WAY TOWARD THE MINIMUM AIR VALVE POSITION THROUGH THE N/O
CONTACT OF (R21) AND THE
(VM1), THROUGH THE N/C CONTACTS OF (R20) AND (R23), POSITIONS THE BURNER AIR AND GAS CONTROL VALVES TO MINIMUM AFTER A RUN CYCL
E. WHEN (R20) IS ENERGIZED
THE AIR CONTROL VALVE WILL BE RE-POSITIONED TO THE MAXIMUM POSITION FOR THE PREPURGE AND THEN RETURNED TO THE MINIMUM POSITION
FOR LOW FIRE START.
THE BURNER AIR CONTROL VALVE WILL BE AT THE MINIMUM POSITION DURING OFF CYCLES. UPON A CALL FOR HEAT OR ANY OTHER TIME THAT A
PREPURGE CYCLE OCCURS
THE EARLIER DESCRIBED PREPURGE CYCLE WITH THE WIDE OPEN AIR VALVE WILL BE REPEATED.
IF AN ATTEMPT IS MADE TO RESTART THE BURNER BY RESETTING THE FLAME SAFEGUARD, OR IF AN AUTOMATIC RESTART IS INITIATED AFTER FLA
ME FAILURE,
IF THE UNIT OVERHEATS, THE HIGH LIMIT CONTROL (FLC) WILL CYCLE THE BURNER, LIMITING FURNACE TEMPERATURE TO THE LIMIT CONTROL SE
T POINT.
SEQUENCE OF OPERATION
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
(Schematic c
ontinues on pr
evious page
.)