The wiring diagram in the service manual indicates that this is done with a second swith in parallel with the normal air conditioning control and its light. It also indicates that in order to get at this piece of wiring, you'll need to remove the radio and the right half of the driver's dash controls. Fortunately, this is not so. You can remove only one panel with one screw and remove the electrical connector on this switch in less than five minutes.
The panel you want is the one under the radio. It is held on with only one screw and some spring clips. You will need an L-shaped tool to pull off the spring clips, such a miniature prybar
Once you've removed the panel, you're going to want to lie on your
back on the passenger seat, looking upward. The switch will now
appear to be on the right side, because you are upside-down.
It will not be easily identifiable as a microswitch from the bottom;
it will be an unidentified black blob with a three-wire connector on
it. You will identify it by the connector. One of the pins on the
connector is offset from the other two. The center pin is not
connected. The service manual says the wires should be white and
blue, but on my car (2010) they were white and purple instead. Figure
2 shows what this connector will look like. There is nothing at all
similar anywhere near it, so it should be straightforward to find
visually. Note that the service manual shows a two-part connector,
but on my car, it was all one piece.
Once you have found the connector and the switch, use a small flathead screwdriver to remove the connector from the switch. This connector is friction-fit only, and there is no positive locking latch anywhere which you need to squeeze. This makes the removal extremely straightforward.
Optionally, tape the connector out of the way so it doesn't rattle.
Once you have performed this modification, the air conditioner will
no longer be forced on, and you can control whether or not it runs
using the button as usual.