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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
FAN
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
STAGE 3
HEAT
CHANGEOVER
RELAY
ENERGIZED
STAGE 2
IN HEAT
NOTE
B
W1
W2
W3
HEAT
HEAT
RELAY
RELAY
STAGE 1
STAGE 3
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
W3
C
R
HEAT
RELAY
LIMIT OR
SAFETY
SWITCHES
ACCESSORY
RELAY N.O.
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
!
24 VAC
120 VAC
HEATING
24 VAC
TRANSFORMER
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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