5
CAUTION
!
NOTE
NOTE
C
R
O
B
CHANGEOVER
ENERGIZED
IN HEAT
CHANGEOVER
ENERGIZED
IN COOL
G
FAN
RELAY
HEAT
RELAY
STAGE 1
HEAT
RELAY
STAGE 2
HEAT
RELAY
STAGE 3
THERMOSTAT
CONTROL
CIRCUIT
24 VAC
120 VAC
HOT
NEUTRAL
THERMOSTAT
SYSTEM
COMPRESSOR
CONTACTOR
STAGE 1
Y1
COMPRESSOR
CONTACTOR
STAGE 2
Y2
W1
W2
W3
Figure 5. Typical wiring diagram for two-transformer systems with NO safety circuits
TWO COMMONS MUST
BE JUMPERED TOGETHER!
HOT
NEUTRAL
120 VAC
24 VAC
CUT AND
TAPE OFF!
DEPENDING ON SYSTEM
REQUIREMENTS, REPLACE WITH
A 75VA TRANSFORMER, IF NEEDED
Relay contacts shown are thermostatically operated. The
accessory relay scheme is required when safety circuits
exist in both systems.
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.
IF SAFETY CIRCUITS ARE IN ONLY ONE OF THE
SYSTEMS, REMOVE THE TRANSFORMER OF THE
SYSTEM WITH NO SAFETY CIRCUITS.
C
R
O
B
CHANGEOVER
ENERGIZED
IN HEAT
CHANGEOVER
ENERGIZED
IN COOL
G
FAN
RELAY
HEAT
RELAY
STAGE 1
HEAT
RELAY
STAGE 2
HEAT
RELAY
STAGE 3
THERMOSTAT
CONTROL
CIRCUIT
24 VAC
120 VAC
HOT
NEUTRAL
THERMOSTAT
SYSTEM
COMPRESSOR
CONTACTOR
STAGE 1
Y1
COMPRESSOR
CONTACTOR
STAGE 2
Y2
W1
W2
W3
Figure 6. Typical wiring diagram for two-transformer systems with safety circuits in BOTH systems
TWO COMMONS MUST
BE JUMPERED TOGETHER!
HOT
NEUTRAL
120 VAC
LIMIT OR
SAFETY
SWITCHES
LIMIT OR
SAFETY
SWITCHES
LIMIT OR
SAFETY
SWITCHES
24 VAC
LIMIT OR
SAFETY
SWITCHES
COMMON
COMMON
HEATING
TRANSFORMER
COOLING
TRANSFORMER
24 VAC
ACCESSORY
RELAY N.O.
CONTACT