Actually my potentiometer is doing a whole lot, it's almost set as high as another 100k ohm resistor.

This is set up in parallel, which means it is a type of controlled "voltage leak" around the stock sensor. The higher the resistance on this extra circuit, the smaller the "leak", and therefore the closer to the stock setting it is. As the computer sees more current (when the sensor has lower resistance) it sees higher temperature, so to give it a little more current we "leak" a little from one wire of the sensor to the other to trick it into seeing a higher temperature. Higher temps, more AC to compensate.

Wow it can get cold, I turned it down to about 160k for a little test today and holy crud it was like sticking my arm into a freezer! Had to turn that knob back up. I know it would form ice at that temperature.

 

It would be really cool if you could somehow rig that up to a rotary switch and power button in the same switch. I dunno if something like that exists.

 

Don't have a manual for my '09 Fit but went ahead and bought a factory thermistor (about $10) so that I could put it in an ice bath and thermometer and record resistance. I thought I would just add resistance sufficient to raise the sensor output by about 2 - 3 degree F. Figured I would just tuck the resistor leads into the thermistor connector itself - a no fuss installation. And I figured that there is probably sufficient margin in the cycling setpoint of the existing setpoints to accomodate the 2 - 3 degree F without any adverse impact.

Your setup does allow a lot more control... and should especially be very effective for the guy in Phoenix where the humidity is low.........

I was surprised when you mentioned that the Euro version has a different cycling point / thermistor.

 

Its extremely hot here in the desert, so I wondering
will this mod work if my evap temps are already high inside the car?
because it seems the fit will cycle on and off the compressor no
matter what the temp is for fuel economy.

I guess what I really want is the fit to cycle only when the evap temps
get to freezing, and not cycle the compressor for fuel economy.

 

I think you're kind of assuming/insisting that the A/C cycle is not dependent on operating temps in the system and is timing based. That would seem to be an incorrect conclusion as this man's mod has evidently worked perfectly.

 

The compressor cycling is due to the the temperature at the thermistor and when the weather is cold it does the same when set on the defrost mode as it does in the summer on the A/C setting.

 

Yes, I'm assuming the cycling isn't dependant on the thermistor.
I just don't understand why the compressor keeps cycling off
when its 114F outside, and 140F inside the car, shouldn't
the compressor stay on until it reaches, say 45F at the thermistor?

 

Jimmy you are going to have to go back and read polaski's opening post.... He explains everything very well but it is somewhat technical and I had to go over it a few times to get a general idea and will have to do so many times again as I do the mod.... For reasons of economy Honda chose to utilize a thermostat that only allows the A/C to cool the air to 55 degrees and then cut off at that temperature.

 

You would think. I think it is getting cold enough at the evaporator to make it cycle, but since that isn't really very cold it takes forever to cool down all that ductwork under a hot black dash which is why you feel hot air blowing out for 10 minutes.

When the temp is set to cycle around 34 degrees it seems to take forever to get there, so mine doesn't cycle all that much anymore (which is good when first getting into the car). And yeah, it sucks the gas with that button pushed in. This isn't going to be a good tank because I've been enjoying the AC so much.

 

I was just wondering today, if I got a few extra parts and made a few of these to use up my resistors, would anyone want one? Not given away, of course, my time is worth something

I was considering an indicator light but that might be a lot of work involving a separate power wire, an LED, a fuse and a relay.

 

I would be tempted to buy one from you (or do the mod myself) but my AC already causes the vents to form condensation sometimes, even though I'd like it colder a lot of the time. I'm too nervous about freezing up my system, I think mine is fine it's just on a hot CA day I'll always want more.

EDIT: I could always change my mind, how much would you sell the kit for shipped?

 

A certain someone keeps telling me I need to mass produce these especially after sitting in my car today. He called it "the arctic car". It was 90 outside with humidity so high that everything has been dripping wet without any rain, I think they said RH finally came down to 94% or so late this afternoon. In the car it was right around 50 degrees after 5 minutes of idling and I froze out by the time I got home because I never had to turn it down, with the fan on 2 with my old half-clogged cabin filter in there. The evaporator never froze. A weird thing, for the first 10 minutes I could see where the vent ducting goes under the dash because the water condensed on TOP of the dash (not on the vent! I was surprised).

If I start making these en masse, keeping it the same as my prototype setup (which I probably will for at least a while) the cost would likely be $30 including shipping to the continental US. I know people in places hotter than here would REALLY appreciate a strong AC system, and not everyone has the know-how of electronics, or doesn't want to spend money on a soldering iron and a multimeter that they'll likely only use once.

Before that I want to do what I was thinking before, using up the extra components I have (I figure I have enough resistors for 2 more), and just factor the cost of the two switches, potentiometers, better wire for running under the dash, and shipping for these "test" units. If it's cheap enough I'll just ship it for free to the two people I like the most, haha. That way I can get a couple other people's opinions on how well it works and if it's worth it for me to do more with this.

 

Am I correct in thinking that the length of the wires is a crucial variable with this mod? The length of the wire also determines the amount of *leak*, right?

 

No. The wire itself has such an insignificant amount of resistance compared to these resistors that you could probably run it a hundred feet before you could even measure a difference.

 

Okay, that messes with my understand of this a little. You described it as a controlled leak, and the resistors lessen the amount of the leak. So if the length of wire with no resistors would make no change to the A/C, and adding another resistor would make the A/C not as cold.... do you see how these contradict eachother? It would seem that the more resistors you take away, the warmer the A/C would get until it goes back to stock.

So if your A/C gets too cold wouldn't you remove a resistor?? I just don't understand how when you turn your potentiometer down the A/C temperature drops if the circuit itself is not a significant leak. Are you really turning the potentiometer up when you make it colder???

 

This is why I'm offering to build them lol, it takes a little understanding of electronics to do it...

If there were no resistors, the computer would see no voltage difference and think the temperature at the evaporator is 500,000,000,000,000,000,000,000,000,000,000 degrees fahrenheit so it would never cycle the system.

Since this is a bypass, the greater the resistance we use, the closer to stock temperature we are. Turn down the pot, resistance goes down, and thus we allow more current to pass and are farther away from the stock setting.

 

I just went and looked at the first page again to see the pic of how you spliced into the thermistor and it makes a lot more sense now. I hadn't been imagining when the circuit is engaged, the stock thermistor is completely not being used. I was imagining your circuit was working to add more resistance to the thermistor. :P Thanks for having patience with me!

 

When I bought my 07 fit at I didnt like the ac. I live in florida and the ac feels a little weak. I have insulated the lines in the engine bay thinking that would help but no. So I am interested in this.


Joe

 

I'll take one!

jerij

 

Update... I have almost all the parts needed to start working on the first one and am starting it tonight. Just need connectors.

I have already PM'd the first candidate for it (he responded first via PM).

When the next ones follow depends on his input and me sourcing a better supplier for parts than Radio Shack. I wiped them out of switches tonight and I only bought ONE. Yup, need bulk. When everything falls into place for purchasing them I'll make a thread in the appropriate forum and link to it from here.