208 Print Reading for HVACR
Copyright Goodheart-Willcox Co., Inc.
L1 L2
X-FRMR
1
CP
COIL
VDM
VD
GV
STAT
LIM
24 V
3
4 6
A
L1 L2
X-FRMR
1
CP
COIL
VDM
VD
GV
STAT
LIM
24 V
3
4 6
B
L1 L2
X-FRMR
1
CP
COIL
VDM
VD
GV
STAT
LIM
24 V
3
4 6
C
L1 L2
X-FRMR
1
CP
COIL
VDM
VD
GV
STAT
LIM
24 V
3
4 6
D
Goodheart-Willcox Publisher
Figure 9-10. A—The transformer supplies power to the low-voltage control circuit. B—The relay coil is energized when the space
thermostat closes its contacts. C—When the relay coil is energized, both sets of normally open contacts on the relay close.
D—Once vent damper motor operation has opened, the VD contacts close and the gas valve is energized.