McQuay IM 987
79
Wiring Diagrams
Figure 87: Standard Mod, Furnace Control (1000 MBh), Continued
PRESS. REG.PRESS. REG.
AIR
SWITCH
AIR
SWITCH
CONN.
TEST
COCK
TEST
CONN.
TEST
COCK
TEST
MAIN GAS VALVES
GV3
PILOT VALVE
MAIN GAS VALVES
GV3
PILOT VALVE
BLOWER
BURNER
BLOWER
BURNER
GV1
CONN.
TEST
GV1
GV2GV2
PIPING DIAGRAMPIPING DIAGRAM
PILOT
REG.
MAIN
PRESS.
PILOT
REG.
MAIN
PRESS.
COCKCOCK
CONN.
TEST
OVER 1/2 P.S.I.
HIGH PRESS.
(THRU 1/2 P.S.I.)
OVER 1/2 P.S.I.
HIGH PRESS.
(THRU 1/2 P.S.I.)
REG.REG.
SHUTOFFSHUTOFF
COCKCOCK
SHUTOFFSHUTOFF
COCK
AIR
COCK
VALVE
GAS
MOD.
DAMPER
AIR
VALVE
GAS
MOD.
DAMPER
UPON DETECTION OF PILOT FLAME, TERMINAL #10 (IGNITION TRANSFORMER--IT) WILL BE DE-ENERGIZED AND TERMINAL #9 (MAIN GAS VALVES--G
V2 & GV3)
THE BURNER COMBUSTION AIR BLOWER MOTOR (BM). WHENEVER POWER IS RESTORED TO THE FLAME SAFEGUARD, THE FLAME SAFEGUARD WILL GO T
HROUGH A 10 SECOND
CONTROL (FLC) AND TERMINAL #6 ON THE FLAME SAFEQUARD (FSG) IS POWERED. THE FLAME SAFEGUARD THEN ENERGIZES ITS TERMINAL #4, WHIC
H POWERS
(BO#9) OR (BO#10) ON THE MAIN CONTROL BOARD (MCB) ARE CLOSED THE ACTUATOR WILL REMAIN AT ITS PRESENT POSITION. THE HEATING CA
PACITY IS MONITORED BY THE
POSITION. WHEN THE MAIN CONTROL SYSTEM CLOSES (BO#9) ON THE MAIN CTRL BRD.(MCB), THE ACTUATOR WILL REPOSITION TOWARD A LOWER
FIRING RATE. IF NEITHER
MAIN CTRL BRD.(MCB), THE GAS VALVE ACTUATOR WILL REPOSITION TOWARD A HIGHER FIRING RATE UNTIL EITHER (BO#10) OPENS OR THE ACTUA
TOR REACHES ITS MAXIMUM
GAS VALVE AND COMBUSTION AIR DAMPER AND CAN SET THE FIRING RATE BETWEEN 33% AND 100% OF NORMAL RATE. WHEN THE MAIN CONTROL SYS
TEM CLOSES (BO#10) ON THE
WHENEVER THE BURNER IS IN OPERATION ITS FIRING RATE WILL BE DETERMINED BY THE "FLOATING" GAS VALVE ACTUATOR (VM1). THIS ACTUAT
OR POSITIONS THE BUTTERFLY
MAIN CONTROL BOARD (MCB) THROUGH (AI#10) VIA A POSITION FEEDBACK POTENTIOMETER ON THE ACTUATOR (VM1).
SAFEGUARD (FSG). UPON A CALL FOR HEAT, THE CONTROL SYSTEM WILL CLOSE (BO#11) ON THE MAIN CTRL BRD (MCB), THUS ENERGIZING RELAY
(R20).
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)
POWER IS FURNISHED THROUGH THE SYSTEM ON-OFF SWITCH (S1), THROUGH THE BURNER ON-OFF SWITCH (S3), THROUGH RELAY (R20) CONTACTS,
THROUGH THE HIGH LIMIT
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
DE-ENERGIZED, THUS DE-ENERGIZING THE BURNER. THE FLAME SAFEGUARD WOULD THEN BE ON SAFETY LOCKOUT AND WOULD REQUIRE MANUAL RESE
TTING. THE HEAT ALARM
ALSO, THE FLAME SAFEGUARD CONTAINS "LED'S" (LOWER LEFT CORNER) THAT WILL GLOW TO INDICATE OPERATION.
BLOWER OPERATION IS SENSED BY THE AIR SWITCH (AS), WHICH MAKES TERMINAL #6 TO #7. AFTER A 90 SECOND PREPURGE PERIOD, TERMINAL
#8 (FIRST GAS VALVE
THE RELAY DRIVES THE GAS VALVE ACTUATOR (VM1) TO THE MINIMUM FIRING RATE POSITION WHENEVER THE FLAME IS NOT
RELAY (R24) WOULD THEN BE ENERGIZED AND WOULD THEN ENERGIZE THE REMOTE "HEAT FAIL" INDICATOR LIGHT AND SEND A FAIL SIGNAL TO BI
NARY INPUT #5 ON THE
IN THE EVENT THE PILOT FAILS TO IGNITE OR THE FLAME SAFEGUARD FAILS TO DETECT ITS FLAME WITHIN 10 SECONDS, TERMINALS #4, 8, 9,
AND 10 WILL BE
IF THE UNIT OVERHEATS, THE HIGH LIMIT CONTROL (FLC) WILL CYCLE THE BURNER, LIMITING FURNACE TEMPERATURE TO THE LIMIT CONTROL SE
T POINT.
INITIATION PERIOD BEFORE THE PREPURGE PERIOD WILL BEGIN.
MICROTECH II MAIN CONTROL BOARD (MCB).
WILL BE ENERGIZED AND THE MAIN FLAME WILL COME ON.
THE FLAME ROD (FD).
(PILOT)--GV1) AND TERMINAL #10 (IGNITION TRANSFORMER--IT) WILL BE ENERGIZED.
ON, AND HOLDS IT THERE UNTIL THE FLAME HAS LIT AND BEEN PROVEN.
LOW FIRE START IS PROVIDED BY RELAY (R23).
SEQUENCE OF OPERATION
THE PILOT FLAME WILL IGNITE AND BE DETECTED BY THE FLAME SAFEGUARD THROUGH
WHEN 120 VOLT
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(Schematic c
o
ntinues on the pr
evious page
.)