Great mod. Just performed it and had some trouble unplugging the wire (no screwdriver available). The Fit's key worked real well for this. Now I can drive around all the time on defrost and low blower which is great in cold weather.

My only concern is now there is a very distinct click sound when switching to the defrost blower. I don't think it did that before but I'm not sure. Anyone else noticed this? Much less annoying than the compressor cycling though.

 

thanks. this was easy to do and fixed something that was annoying the p^ss out of me.

 

Out of curiosity why do you want to disable a/c in defrost when the major purpose of the a/c is to remove moisture before it condenses on cold windows ?

 

Is the defroster just as effective without the AC?

 

In cold weather, the heat is mostly enough to defrost the windows - and it doesn't get dampened by the A/C being on. You can still manually run the compressor by hitting the A/C button. Don't understand why Honda did this, as the new Civics and Accords allow you to turn off A/C with defrost.

 

Can't be.The ojective is to blow warm DRY air across windows or windshield, not warm wet air which would have more moisture content to condense on cold surfaces.
Thats why manufacturers do it in the first place.
And why its best on recirculating mode without fresh air makeup.

 

The warmer the air the more moisture the air will hold so heat alone isn't the answer until the air is dehumidified by a/c They allow turning off a/c after air has been dehumidifed and air is warm and dehumidified to save mpg losses to a/c compressor. Til then there is more moisture condensed on cold surfaces and it takes longer for the warm air to absorb the water. i.e. undue the condensation.

 

It is, but depends on the condition. If outside air coming in is wet, then the air coming out of the vents will not dry the windows. You need the AC at this point to dry the air.

If the air outside is very cold i.e. less than 32 F, then the air is dehumidified by nature. Operating AC is not needed at this point. It reduces the amount of heat applied to the window, and reduces gas mileage.

Car manufacturers build these systems like this because most people don't know these facts. With this information, you can determine if you need the AC or not.

 

Except for all of the hot wet air coming out of the vehicle occupants' faces and being trapped in the car.

Which is why in cold weather you want the recirc OFF to draw in the cold, dry air from outside as well as the AC on to remove the moisture in your breath.

I have never experienced a situation where running the defrost without A/C worked as well as running the defrost without. In my '02 Civic I enabled the "hack" that allows you to turn off the AC compressor and in conditions where the windshield fogs up, when I turn on the AC the fog goes away, when I turn it off it comes back within minutes.

 

This makes sense, but do you have a source for this information? I really don't care that much one way or the other; I'd like to have manual control over AC in defrost, but I rarely keep it on defrost unless it's a very wet/humid day, but if it's going to turn off the AC automatically after some period, all the better.

I decided to actually RTFM (novel idea -- I should do it more often). Page 113 says:

 

This isn't a one-way-works and-the-other-doesn't situation. The A/C compressor does dehumidify the air and is helpful for defogging, even necessary if you're using recirculate mode. Outside air heated by the core but not further dehumidified by the A/C often works just fine, though, just like a hair drier will defog a bathroom mirror without an A/C unit attached for dehumidification.

So the A/C will dehumidify the air but also make it less hot than it would be without the A/C, and it also uses more gas. This is great for extreme fogging, but not always needed. The factory setup only gives one the option to use a sledgehammer even when that's more than required for the job.

 

There's no indication the A/C will deactivate after a while in defog/defrost mode. I wouldn't expect it to.

Also Mahout's comment "its best on recirculating mode without fresh air makeup" is dead wrong (Honda agrees!). Sorry Mahout. Without fresh air, without the A/C running, you will fog up the interior. On recirculate, running the A/C to remove moisture is mandatory; there's no other way to remove moisture. Bringing in fresh cold outside air, even if it's at 100% humidity, when warmed by the heater will have relatively low humidity. Relative humidity is a function of temperature and dew point. The warmed air has a greater capacity to hold moisture, so it will have a drying effect even without the A/C running. Interior humidity will not increase because the air is then exhausted (because you're not on recirculate).

The combination of warmed outside fresh air, and running the A/C will result in even dryer air (lower relative humidity) providing the best defogging function.

txmatt is correct, however unless you leave it in defog all the time (who does this besides those that leave it on recirculate all the time?) the gasoline issue is probably not measurable.

I am curious if the A/C will run when the ambient temps are below 40F. The temperature sensor on the evaporator should disable the A/C, but anecdotal evidence from our northern neighbors refutes this theory.

Bit chilly outside today (damn Canadian air). I'll have to experiment.

 

since i disabled the A/C defog on the second of jan, it has rained non-stop in my region. i have had to run the defog the entire time i have been driving since then (about 400km). i have been so happy to think of the fuel that i am saving, the lack of cycle-clicking and dimming, and less wear on my A/C.

the defog has worked just fine without the A/C (which i can still easily turn on by pressing a button if i so wish). with the exception of start up, there has been no fog issue whatsoever, and the start up fog dissipates easily enough. i recommend that anyone in the northwest, with our p^ssy winters, should give this a try and begin watching the fuel savings add up.

thanks again roger. btw, i notice that your sig lists "modified dome light" and "filter mag". can you tell me what those mods are?

 

How much fuel are you saving?

 

About 20F in the parking garage when I left work last night. I took a moment to try the defog. The A/C compressor kicked in. (I had been skeptical it was actually running below freezing.) It's a mystery to me why the evaporator thermostat (thermistor?) doesn't keep it from running. Any A/C mechanics here? rhyneba?

I agree with the others it would be annoying to use the defroster to melt ice off the outside and have the A/C engage by default. Defog not so much. If I didn't have covered parking I'd be yanking out the wires too.

Do newer American/European cars behave this way or is it just Asian?

 

There is nothing wrong with creating the option of not running AC with defrost/defog. Honda probably did it the way they did because lawyers will look for anything for a class action suit.

Yes with AC on it will defog faster, but it may work slower when defrosting.

To the OP:
Nice DIY thanks!

 

Defrosting means undo idling. I don't count on it for defrost initially, before I start driving. I scrape the windshield as clean as I can while the car warms up for two minutes and then while driving defrost/defog does the rest, and it does it very effectively and quickly. I WOULD like the choice to disable the AC but it just doesn't matter much to me with defogging and now lately, defrosting. It's effective and quick and when the winshield is clear I switch it off, or to dash/floor for heat. It hasn't really put a dent in fuel consumption either, far as I can tell. Perhaps if it was on constantly, but I don't find a need for that. All things considered, it's not enough motivation to do this mod, for me. The system works quite well and I don't like to fix what ain't broke- especially wanking wires. But that's just me.

Dan

 

I just added all my web pages for my mods to my signature line.

The filter mag: go here:FilterMAG: Magnetic Oil Filters finish the Job Your Filter Started.

I used it from the beginning, and I left in place while I removed and cut open the first oil filter. It did have fine particles similar to the picture, but of course, no where near that amount of wear particle.

 

i don't have exact numbers for you at this time. it's difficult to calculate on a per-tank basis because the weather is never the same for each tank. i also am unaware of the exact draw of the fit's compressor.

so far, for this current tank of gas, i have had to run defog for the entire tank up until today. it has been very wet around here. that would have been constant AC cycling for the entire tank, whether at idle or driving (100% city so far this tank).

the EPA claims that running A/C either at idling or at low speeds can reduce fuel efficiency by anywhere from 4%-25% depending on the vehicle. i bought this car mostly for the economy and anything i can do to improve mileage is a big plus for me, especially since my own findings have shown it to make minimal difference to how well my car defogs. it's just a waste of energy and i hated it since the first day i bought the car and noticed it. that's why "ROGER'S FIT" is sort of like a God to me in this forum.

 

Edit: A more in depth reply.

Thanks to one of the other members' posts i did this in 5 min flat.

-In order to save the panel from being damaged, just use a terry towel along with a small allen wrench to slide and pry at the same time along the bottom of the panel.
-Use a small flathead screwdriver to pop out the connector.
-Presto!