I have an electric air conditioning unit at home. I am able to override the remote control unit and rely on a time clock attached to the wall. The time clock has levers, which, when pressed in, makes the unit come on, and when not pressed in, means the unit will not come on. Can the time switch (that is, the levers) be altered during Shabbat if that alteration will not have any affect on power at the time the alteration is made? Can the time the unit is on be lengthened or shortened? Can the alteration be made whether or not the unit is on at the same time? Many thanks.

The basic rule is: you can extend the current position; you can’t shorten it. If it is on, you can keep it on longer, if it is off you can keep it off for longer. See Shmirat Shabbat Kehilchata 13 25-26; 23 22.