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CHANGEOVER
CUT AND
ENERGIZED
TAPE OFF!
IN COOL
HOT
120 VAC
24 VAC
NEUTRAL
Figure 5. Typical wiring diagram for two-transformer systems with NO safety circuits
NOTE
Relay contacts shown are thermostatically operated. The
accessory relay scheme is required when safety circuits
exist in both systems.
O
Y1
Y2
CHANGEOVER
COMPRESSOR
ENERGIZED
CONTACTOR
IN COOL
STAGE 2
COMPRESSOR
CONTACTOR
RELAY
STAGE 1
TWO COMMONS MUST
BE JUMPERED TOGETHER!
Figure 6. Typical wiring diagram for two-transformer systems with safety circuits in BOTH systems
IF SAFETY CIRCUITS ARE IN ONLY ONE OF THE
SYSTEMS, REMOVE THE TRANSFORMER OF THE
SYSTEM WITH NO SAFETY CIRCUITS.
O
Y1
Y2
G
COMPRESSOR
CONTACTOR
STAGE 2
COMPRESSOR
FAN
CONTACTOR
RELAY
STAGE 1
TWO COMMONS MUST
BE JUMPERED TOGETHER!
G
B
W1
W2
HEAT
RELAY
STAGE 1
HEAT
CHANGEOVER
FAN
RELAY
ENERGIZED
STAGE 2
IN HEAT
NOTE
B
W1
W2
A1
HEAT
RELAY
DAMPER
STAGE 1
HEAT
CHANGEOVER
RELAY
ENERGIZED
STAGE 2
IN HEAT
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.
THERMOSTAT
CONTROL
CIRCUIT
A1
C
R
DAMPER
LIMIT OR
SWITCHES
LIMIT OR
SAFETY
SWITCHES
COMMON
THERMOSTAT
CONTROL
CIRCUIT
THERMOSTAT
R
C
SYSTEM
HOT
24 VAC
120 VAC
NEUTRAL
DEPENDING ON SYSTEM
REQUIREMENTS, REPLACE WITH
A 75VA TRANSFORMER, IF NEEDED
CAUTION
!
SAFETY
24 VAC
120 VAC
HEATING
24 VAC
TRANSFORMER
ACCESSORY
RELAY N.O.
CONTACT
COMMON
LIMIT OR
SAFETY
SWITCHES
24 VAC
120 VAC
COOLING
TRANSFORMER
THERMOSTAT
SYSTEM
LIMIT OR
SAFETY
HOT
SWITCHES
NEUTRAL
HOT
NEUTRAL
5
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