publication

178 / 221

INTEGRATED
FURNACE CONTROLS
21M51U-843 WIRING
AND CONFIGURATION
HOT
(LINE)
50M51-843 TYPICAL WIRING DIAGRAM
NEUTRAL
(LINE)
120 VAC
24 VAC CLASS II
TRANSFORMER
50M51-843
24 VAC
TH TR
COOL
PARK
HEAT LO
HEAT HI
LINE
XFMR
EAC
HUM
CIRCU-
LATOR
BLOWER
INDUCER
HUMIDIFIER
(OPTIONAL)
ELECTRONIC
AIR CLEANER
(OPTIONAL)
IGNITOR
IGN
IND HI
IND LO
IND N
IGN N
CIRC N
LINE N
XFMR N
HUM N
EAC N
R
W2
W1
Y
YLO
R
W2
W1
Y2
Y1
COMPRESSING
UNITS
50M51-843
in other
furnace
(Trane
application)
THERMOSTAT
FLAME
SENSOR
PROBE
(Lennox only)
2ND STAGE PRESSURE
SWITCH (N. O.)
HIGH LIMIT
(N. C.)
AUX. HIGH
LIMIT (N. C.)
1ST STAGE PRESSURE
SWITCH (N. O.)
GAS
VALVE
HLO
HLI
FP
PS1
MVL
MVH
GND
GND
PS2
MV COM
TR
TH
Low Voltage (24 VAC)
Line Voltage (120 VAC)
G G
ROLLOUT
SWITCH (N. C.)
LEGEND
N. C. = Normally closed switch
N. O. = Normally open switch
TWIN
C
Twin
Application
Only
FP2
179
TECHNICAL HELP