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Old 01-06-2013, 01:12 AM   #1 (permalink)
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Toyota Matrix Defrost Mod

Like most vehicles, my wife's Toyota Matrix turns the A/C on to dehumidify whenever the defrost or defrost/floor settings are selected. Since we live on the wet coast, defrost is used most of the time to keep the windshield defogged. Therefore, the A/C is usually on.

Today I got thinking. The Matrix has a separate A/C switch, so why not modify it so the defrost does not automatically turn the A/C on, and if dehumidification is necessary simply hit the A/C button and leave it on for half a minute?

A quick look at the Matrix wiring schematic revealed that the single yellow wire going into the heat position selector needed to be snipped.

I removed the radio and went in from above because I did not have the tools to unclip the panel that encloses the heater controls.

That's it! It works great. Less A/C time will equate to less fuel consumption.

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Old 01-06-2013, 01:16 AM   #2 (permalink)
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Awesome. I'd like to look into this for my girl's Xd, although the answer is probably no.
Also, if need be, you could pull just pull the pin in the connector and tape it into the harness.
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Old 01-06-2013, 09:44 AM   #3 (permalink)
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Nice mod. I really wish that the automakers never started doing this stupid thing. At the very least they could allow you to turn it off, but they don't even let you do that.
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Old 01-06-2013, 12:38 PM   #4 (permalink)
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Good job! I did this to my truck during the summer of 2010, and it does provide a noticeable change in fuel consumption.

Unfortunately, I can't do this to my Magnum - they replaced a single A/C wire (that would normally come out of the control panel and go to the engine computer) with a bloody CAN-B mux signal! Oh, well - I can still yank the A/C clutch control relay for now, and toss it into my glove box against the return of summertime.
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Old 01-06-2013, 12:48 PM   #5 (permalink)
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That's too bad....but I guess CAN bus is the new way. I deal with it every day at work, and it does work well overall. On the HD diesels I work on, even the engine talks to its components over E-CAN....the ECM with turbocharger, EGR valve, humidity sensor, NOx in and out sensors, DOC/DPF temps, SCR pump, etc, etc., all over a two wire bus. Kind of crazy....

In your case, I guess you could install another relay on the A/C clutch circuit to a toggle switch on the dash so you have the option to dehumidify if you need to.
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Old 01-07-2013, 02:09 AM   #6 (permalink)
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I drove 125km (78mi) today, all in 5C (41F) pouring rain, 100% humidity weather with my wife and kids in the car. Defrost on the whole entire time.
Nothing fogged up. No need for A/C.
Now I am even more happy that I cut the yellow wire.
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Old 01-07-2013, 09:32 AM   #7 (permalink)
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I pulled the plugs to the compressors on my 97 Ranger and 2011 Fiesta. Mileage is better and no problem with defrosting.

regards
Mech

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