White Rodgers 1F91-71 - Manual (Page 5)

5
IF SAFETY CIRCUITS ARE IN ONLY ONE OF THE
SYSTEMS, REMOVE THE TRANSFORMER OF THE
SYSTEM WITH NO SAFETY CIRCUITS.
NOTE
Heat
Relay
Stage 2
Compressor
Contactor
Stage 1
Changeover
Energized
In Heat
Compressor
Contactor
Stage 2
Thermostat
Control
Circuit
Limit or
Safety
Switches
Limit or
Safety
Switches
Figure 5. Typical wiring diagram for two-transformer systems with NO safety circuits
DEPENDING ON SYSTEM
REQUIREMENTS, REPLACE
WITH A 75VA TRANS-
FORMER, IF NEEDED TWO COMMONS MUST
BE JUMPERED TOGETHER!
CUT AND
TAPE OFF!
Changeover
Energized
In Cool
24vAC 120vAC
Hot
Neutral
THERMOSTAT
SYSTEM
TRANSFORMER
24vAC 120vAC
Hot
Neutral
TRANSFORMER
O B Y1 Y2 G W1 W2 R W3 C
Heat
Relay
Stage 3
Heat
Relay
Stage 1
Fan
Relay
CAUTION ! NOTE
Polarity must be observed. If the HOT side of the
second transformer is jumpered to the COMMON
side of the first transformer, a short will be made.
Damage to equipment will occur when power is
restored. Relay contacts shown are thermostatically operated. The
accessory relay scheme is required when safety circuits
exist in both systems.
Thermostat
Control
Circuit
Figure 6. Typical wiring diagram for two-transformer systems with safety circuits in BOTH systems
TWO COMMONS MUST
BE JUMPERED TOGETHER!
C
24vAC 120vAC
Hot
Neutral
THERMOSTAT
SYSTEM
COOLING
TRANSFORMER
Limit or
Safety
Switches
24vAC 120vAC
Hot
Neutral
Limit or
Safety
Switches
HEATING
TRANSFORMER
Limit or
Safety
Switches
Limit or
Safety
Switches
24vAC
Accessory
Relay N.O.
Contact
Heat
Relay
Stage 3
Heat
Relay
Stage 1
Compressor
Contactor
Stage 2
Changeover
Energized
In Heat
Compressor
Contactor
Stage 1
Fan
Relay
Heat
Relay
Stage 2
Changeover
Energized
In Cool
R W3 W2 W1 G Y2 Y1 B O