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Wiring Diagrams
The following is just a sample of the most common types of HVAC
systems. Refer to your system’s installation manual for wiring information.
5
Hot
Heating
Control
Cooling
Control
Transformer
T
H
E
R
M
O
S
T
A
T
W1
C
R
Y1
G
O
B
24 VAC
120 VAC
HEAT/COOL
4-WIRE
SINGLE TRANSFORMER
Fan
Control
Y2
W2/E
Hot
Heating
Control
Transformer
24 VAC
120 VAC
HEAT ONLY
2-WIRE
SINGLE TRANSFORMER
W1
Y1
G
T
H
E
R
M
O
S
T
A
T
O
B
C
R
Y2
W2/E
HEAT/COOL
2 STAGE
Hot
Transformer
24 VAC
120 VAC
T
H
E
R
M
O
S
T
A
T
R
C
L
W1
Y1
B
O
G
Y2
W2/E
First Stage
Cool
First Stage
Heat
Second
Stage Heat
Second
Stage Cool
Fan
Control
Hot
Cooling
Control
Fan
Control
Transformer
24 VAC
120 VAC
COOL ONLY
3-WIRE
SINGLE TRANSFORMER
W1
Y1
G
T
H
E
R
M
O
S
T
A
T
O
B
C
R
Y2
W2/E
Hot
Heating
Control
Fan
Control
Transformer
24 VAC
120 VAC
HEAT ONLY
SINGLE TRANSFORMER
3-WIRE
W1
Y1
G
T
H
E
R
M
O
S
T
A
T
O
B
C
R
Y2
W2/E
110-1101B 3/4/05 3:56 PM Page 5