It's a way to turn on/off an <a href="https://en.wikipedia.org/wiki/en:Air_conditioning" class="extiw" title="w:en:Air conditioning">Air conditioner</a> by a <a href="https://en.wikipedia.org/wiki/en:Thermostat" class="extiw" title="w:en:Thermostat">Thermostat</a>.
<a href="//commons.wikimedia.org/wiki/User:JohnBulb" class="mw-redirect" title="User:JohnBulb">User:JohnBulb</a> aka <a href="//commons.wikimedia.org/wiki/User:OnionBulb" title="User:OnionBulb">User:OnionBulb</a>
2008-04-12
this png image was made by <a href="//commons.wikimedia.org/wiki/User:JohnBulb" class="mw-redirect" title="User:JohnBulb">User:JohnBulb</a> aka <a href="//commons.wikimedia.org/wiki/User:OnionBulb" title="User:OnionBulb">User:OnionBulb</a>