NOTE
Relay contacts shown are thermostatically operated. The accessory relay scheme is required when safety circuits exist in both systems.
Thermostat
Control
Circuit
!CAUTION
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
O B
Changeover
Energized
In Heat
Y1 G W1
Fan
Relay
E1 | E2 | W2 | C | R |
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Emergency |
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| Heat |
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| Limit or |
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| Limit or | ||||
Relay |
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| Relay |
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| Safety |
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| Safety | ||||
Switched |
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| Hot | ||||||||
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| Switches |
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Output |
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| Stage 2 |
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| 24 VAC |
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| 120 VAC | ||||||||
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Changeover |
| Compressor |
| Heat | |||
Energized |
| Contactor |
| Relay | |||
In Cool |
| Stage 1 |
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HEAT PUMP SYSTEM
TWO COMMONS MUST
BE JUMPERED TOGETHER!
| Emergency |
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| 24 VAC |
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| Neutral |
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| Relay |
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| Constant |
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| Accessory |
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| AUXILIARY |
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| Output |
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| Relay N.O. |
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| HEATING |
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| Contact |
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| TRANSFORMER |
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| AUXILIARY |
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| HEAT PUMP |
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| Limit or |
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| Limit or |
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| HEATING SYSTEM |
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| TRANSFORMER |
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| Safety |
| Safety |
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| Hot |
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| Switches |
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| Switches |
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| 24 VAC |
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| 120 VAC |
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| Neutral |
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Figure 6. Typical wiring diagram for two transformer systems with safety circuits in BOTH systems
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