How to Toggle between Two Heat Pumps using 240V Twin Timer?

Electrical Technology

Wiring Circuit Diagram to Operate One Heat Pump at a Time Using Timer

The following wiring circuit ensures that both heat pumps do not run simultaneously. In other words, only one heat pump (or any other connected load) will operate at a given time. This setup reduces wear and tear on the main breaker, lowers energy consumption, and reduces the electricity bill.

As the outdoor compressor must turn ON before the indoor unit starts cooling or heating, when the 24V AC thermostat sends a signal to the contactor installed for the individual outdoor unit, it activates and begins providing cooling or heating.

Since the contactor is directly connected to 240V AC, it remains active continuously until the associated breaker is turned OFF. The thermostat is used to control the 24V coil circuit via a timer. However, it is not capable of turning off the main contactor.

Inside the access panel of the heat pump unit, a contactor and start capacitor are wired to one terminal of the line wires connected to the compressor motor.

You will notice that the thermostat wires are connected to the side terminals of the contactor. Their purpose is to activate the 24V coil, which, in turn, controls the ON or OFF state of the main contactor, subsequently control the ON/OFF operation of the heat pump unit.

Wiring Circuit

Wire and connect all the components and devices according to the wiring diagram, including the LY2 relay, 3-way switch, and Inkbird twin timer, to the thermostat and contactors via a 120V AC supply within an electrically rated enclosure. Use sheathed wire for the thermostat, as it is sun-resistant and suitable for outdoor applications.

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Working of the Circuit

Two 60A, 240V contactors are used to control the compressor motors of both heat pumps.

The 3-way switch toggles 120V between the relay and twin timer.

When the LY2 relay is OFF, Terminals 6 and 4 are inactive and do nothing. When it’s ON, it ensures the completion of the thermostat circuit for heat pump 1.

When the twin timer is ON, it alternates between turning the heat pumps ON and OFF. When it’s OFF, it completes the thermostat circuit for heat pump 2.