WE CLAIM:
1. An air conditioner comprising:
an outdoor unit;
a relay circuit including a contact and a relay coil; and
a control unit to cause a first voltage equal to or higher than an operating voltage for turning ON the contact or a second voltage lower than the operating voltage and equal to or higher than a retention voltage for retaining a state in which the contact is ON to be applied to the relay coil, wherein
one end portion of two end portions of the contact is connected to an alternating-current power supply and another end portion of the two end portions of the contact is connected to the outdoor unit,
one end portion of two end portions of the relay coil is connected to a power supply for driving the relay circuit, and
the control unit causes the first voltage to be applied to the relay coil at a start of an ON state of the contact, causes the second voltage to be applied to the relay coil after the contact is turned ON, and causes the first voltage to be applied to the relay coil at a predetermined constant period.
2. An air conditioner comprising:
an indoor unit;
an outdoor unit;
a relay circuit including a contact and a relay coil;
a control unit to cause a first voltage equal to or higher than an operating voltage for turning ON the contact or a second voltage lower than the operating voltage and equal to or higher than a retention voltage for retaining a

state in which the contact is ON to be applied to the relay coil; and
an abnormality detection unit to, when an abnormality occurs in the outdoor unit, detect occurrence of the abnormality in the outdoor unit, wherein
the indoor unit includes a notification unit to, when the abnormality detection unit detects that an abnormality has occurred in the outdoor unit, notify that the abnormality has occurred in the outdoor unit,
one end portion of two end portions of the contact is connected to an alternating-current power supply and another end portion of the two end portions of the contact is connected to the outdoor unit,
one end portion of two end portions of the relay coil is connected to a power supply for driving the relay circuit, and
the control unit causes the first voltage to be applied to the relay coil at a start of an ON state of the contact, causes the second voltage to be applied to the relay coil after the contact is turned ON, and causes the first voltage to be applied to the relay coil during a period from detection of occurrence of the abnormality to notification of the occurrence of the abnormality by the notification unit when the abnormality detection unit detects that the abnormality has occurred.
3. An air conditioner comprising:
an indoor unit;
an outdoor unit;
a relay circuit including a contact and a relay coil;
a control unit to cause a first voltage equal to or higher than an operating voltage for turning ON the contact or a second voltage lower than the operating voltage and

equal to or higher than a retention voltage for retaining a state in which the contact is ON to be applied to the relay coil; and
an abnormality detection unit to, when an abnormality occurs in communication between the indoor unit and the outdoor unit, detect occurrence of the abnormality in the communication, wherein
one end portion of two end portions of the contact is connected to an alternating-current power supply and another end portion of the two end portions of the contact is connected to the outdoor unit,
one end portion of two end portions of the relay coil is connected to a power supply for driving the relay circuit, and
the control unit causes the first voltage to be applied to the relay coil at a start of an ON state of the contact, causes the second voltage to be applied to the relay coil after the contact is turned ON, and causes the first voltage to be applied to the relay coil when the abnormality detection unit detects that the abnormality has occurred in the communication.
4. An air conditioner comprising:
an outdoor unit;
a relay circuit including a contact and a relay coil;
a control unit to cause a first voltage equal to or higher than an operating voltage for turning ON the contact or a second voltage lower than the operating voltage and equal to or higher than a retention voltage for retaining a state in which the contact is ON to be applied to the relay coil; and
a monitoring unit to monitor a voltage of the alternating-current power supply, wherein

one end portion of two end portions of the contact is connected to an alternating-current power supply and another end portion of the two end portions of the contact is connected to the outdoor unit,
one end portion of two end portions of the relay coil is connected to a power supply for driving the relay circuit, and
the control unit causes the first voltage to be applied to the relay coil at a start of an ON state of the contact, causes the second voltage to be applied to the relay coil after the contact is turned ON, and causes the first voltage to be applied to the relay coil when the monitoring unit monitors that a voltage of the alternating-current power supply is lower than a predetermined value.