Air conditioner

1 . An air conditioner comprising:

a heat exchanger that exchanges heat between air sent to an air conditioning target space and a flammable refrigerant;

a fan that generates air flow in the heat exchanger;

one of:

a heater that heats the air sent to the air conditioning target space; or

an electric apparatus that is capable of causing electric discharge;

a casing that has:

an arrangement space in which the heat exchanger, the fan, and the heater or the electric apparatus are disposed; and

an opening that communicates the arrangement space with outdoors; and

an opening and closing part that comprises a lid that opens and closes the opening, wherein

the lid opens the opening when the fan is stopped and closes the opening by a negative pressure generated by operation of the fan.

2 . The air conditioner according to claim 1 , wherein the opening and closing part comprises an elastic body that biases the lid when the opening is opened or closed.

3 . The air conditioner according to claim 1 , wherein the opening and closing part opens and closes the opening by rotational movement of the lid or translation of the lid.

4 . The air conditioner according to claim 1 , wherein a weight of the lid causes the opening to be opened or closed.

5 . The air conditioner according to claim 1 , further comprising a filter that covers the opening.

6 . The air conditioner according to claim 1 , wherein the heater is a burner or an electric heater.

7 . The air conditioner according to claim 1 , wherein the electric apparatus is an electromagnetic relay or an electrostatic precipitator.