- 9 -
8. W
IRING
D
IAGRAMS
(
CONT
’
D
)
W
Open: 93.3°C
MRTP 1
MRTP 2
W
Open: 93.3°C
MRTP 1
MRTP 2
24 VAC
COMMON OUT
24 VAC
POWER OUT
CALL FOR FAN
CALL FOR
HEAT 1
CALL FOR
HEAT 2
BL
BK
HEAT INDICATOR
C
G
R
W1
W2
TB
24 VAC
COMMON OUT
24 VAC
POWER OUT
CALL FOR FAN
CALL FOR
HEAT 1
CALL FOR
HEAT 2
BL
BK
HEAT INDICATOR
C
G
R
W1
W2
TB
BL
BL
Season Select
BK
BL
BL
Season Select
BK
Class 2 Transformer
Pri: 240 V 60 Hz
Sec: 24 V 60 Hz 40 VA
Y
T
Y
Y
BK
R
Class 2 Transformer
Pri: 240 V 60 Hz
Sec: 24 V 60 Hz 40 VA
Y
25 kW 240 VAC
Single phase
T
Y
Y
BK
R
Y
Y
BL
BL
W
BK
Recirculation
Mode
R
K1 24V
1
5
2
3
6
4
24V
AC
BK
Recirculation
Mode
R
K1 24V
1
5
2
3
6
4
24V
AC
BL
BL
W
BK
BK
R
C
O
L1
L2
N
G
M
BK
BL
R
Y
BK
BK
K2 240V
1
5
2
3
6
4
240
VAC
NC
BK
K2 240V
1
5
2
3
6
4
240
VAC
NC
R
BK
BL
Y
BK
C
M
BK
BK
R
L1
L2
N
G
O
BL
BK
BK
BK
BK
BK
BK
BK
BL
R1
M6
M5
24V
AC
BL
M2
M1
M4
M3
24V
AC
BL
BL
R
50 A
A2
A1
R2
M2
M1
24V
AC
25 A
R
BK
50 A
M4
M3
HEAT 2
E
ARTP
R
HEAT 3
E
ARTP
R
HEAT 1
E
ARTP
R
HEAT 4
E
ARTP
R
HEAT 5
E
ARTP
R
BL
HEAT 2
E
ARTP
HEAT 3
E
ARTP
R
HEAT 1
E
ARTP
R
HEAT 4
E
ARTP
R
BL
BK
R
BK
BK
BK
BK
BL
R1
M6
M5
24V
AC
BL
M2
M1
M4
M3
24V
AC
BL
BL
BK
BK
B1
50 A
A2
A1
BK
BK
BK
BK
R2
M2
M1
24V
AC
M4
M3
B2
50 A
BK
BK
BK
BL
FE0062A
1. If any of the original wire, as supplied, must
be replaced, use the same equivalent wire.
Wiring must comply with applicable codes,
ordinances and regulations.
2. Field wiring must comply with applicable
codes, ordinances and regulations. Use only
Class 1 wiring inside furnace compartments.
Critical characteristic
Line voltage wiring:
UL AWM 1015/1230, 600V, 105°C, VW-1, 12 AWG;
CSA TEW 600V, 105°C, FT1, 8 AWG and 12 AWG.
Low voltage wiring:
same ratings as high voltage except 18 AWG.
HI
MED-HIGH
MED-LOW
LOW
FAN MOTOR SPEED
BLACK
BLUE
YELLOW
RED
COLOR
LEGEND
C
E
R
K
MRTP
HEAT
L1, L2
Capacitor
Heating Element
Time Delay Relay
Fan Relay
Auto-Reset Thermal Protector
Manual-Reset Thermal Protector
240 V Line Supply
WIRING COLOR CODE
BK
BLACK
BL
BLUE
O
ORANGE
R
RED
W
WHITE
Y
YELLOW
ARTP
M
TB
T
N
Fan Motor
Terminal Block
Transformer Class 2
Heat
Neutral
B
Breaker
For the use of a two-stage thermostat
or an outdoor thermostat, connect
between W1 and W2.
Make sure that the Season Select
switch is set to “Mild” position.
Low power
High power
High power 8 AWG
50 A
BK
R
50 A
R
B3
25 A
BK
R
BK
R
B2
50 A
B1
50 A
R
R
R
BK
BK
BK
R
BK
BK
18/20 kW 240 VAC
Single phase
UL AWM 1015, 600V, 105°C, VW-1, 8 AWG;
WARNING
Risk of electric shock. Disconnect power before installation, servicing, maintenance or field wiring. Replace all panels
before operating. Failure to do so can result in electric shock causing severe injuries or death.
21B18M & 21B20M Models
21B25M
Model
