Many times when driving I use defrost, but don’t necessarily need A/C defrost. For sake of fuel mileage, and A/C system wear and tear, I’d prefer to only engage A/C when I feel it’s needed.
With this aim, I added a bypass switch to the defrost A/C circuit. Result: (1) when bypass switch open, the defrost settings on the ventilation control knob do NOT engage A/C system. However, if the A/C button is depressed, A/C will work as normal. (2) when bypass switch is closed, the defrost settings on the ventilation control knob will engage the A/C system for rapid defrost.

Vehicle is a 2011 Honda Fit Sport (US model)


The “BLU” wire leading vertically upward from the Mode Control Switch is our target. This is where our bypass switch will be inserted. Note, the wire wasn’t actually blue in my vehicle.


Remove plastic cover panel just fwd of shift lever. Gently pry out bottom edge first, then rotate to disengage the tabs along the upper edge.


Position inspection mirror above cigarette socket. The black micro switch is seen in the mirror. This is the switch which engages the A/C system when a defrost setting is selected on the “Mode Control Switch” (knob)


A closer look at the switch leads - wires are (white w/ silver bands) AND (red with silver bands)


The red & white switch wires are reachable from this same access hatch. They’re also visible behind dash when you drop the glovebox, but are much harder to access from glove area. Easiest to access them right at the switch.


Here’s the new bypass switch assembly, as prep’d with soldered leads, and quick disconnects at end of wire leads. The switch itself is a push button (latching) style. Hole (12mm) seen drilled in access panel. Hole center is 49mm from top edge, and 55mm from left (driver side) edge. Use a step-drill for a clean hole.


Gently pry wire connector off the switch with a flat blade screwdriver. With a bit of finger work to release wire clips, the plastic connector is pulled back allowing enough slack in wires to pull one down where you can snip and splice it. Note the wire connector has 3 slots. The middle one isn’t used. One switch wire is cut. Doesn’t matter which one. I used the white one because it has more slack. Butt connectors are crimped on each end, with wire leads attached for supplementary switch. More finger work to manipulate the wire connector back onto the switch. This step took 45 mins! A small pick tool, with a 90 deg. end (“L” shape) proved most helpful to fish the connector back into place. Long nose “mini pliers” also helped.

When reattaching connector, it’s easy to mis-install and not engage contact-tab on side of micro-switch. This results in defrost A/C not working. After two failed attempts (fired up car each time and tested defrost A/C - not working!) I finally got the connector properly seated on both top tabs AND side tab (fired up car and defrost A/C worked - success!).


Here you can see the twisted black/white wires I’ve butt-spliced onto the OEM switch wire to lengthen it. Connected these new wire leads IN SERIES with the new bypass switch using tab style quick disconnects. New wire leads are about 1 ft long, this allows enough slack to remove access panel in future and separate the quick-disconnects. Extra wire was bundle-tied with zip ties, before being stuffed up behind dash.


Finished switch with access panel reinstalled. Again, it’s in series with the stock micro-switch on the ventilation control knob. Thus, when a defrost setting is selected, defrost will only be engaged when this supplementary switch is closed (depressed).

Overall, this job took about a day to complete. It works well, and I appreciate the extra control it gives me. The location of the bypass switch has proven to be a good one. It’s out of view, but easily reachable by the driver as you run your hand down toward the cig. Lighter socket. The switch button itself stands slightly proud when open, and flush when closed, so I can easily “feel” whether bypass is engaged or not, without ever having to look down.

 

This is a great Idea, and I greatly appreciate your time in posting your directions and pictures!. Anyone with a FIT in Florida
will greatly benefit from this hack/upgrade. Thanks!

 

Good post. Been wanting to do something like this on my 2010 Fit for a long time.

Why Honda didn't put separate switches for the AC and defrost is something I never understood.