3rd Gen Auto HVAC Metric Conversion

[rkrenicki]

After a few different attempts at converting my car into Metric for temperatures, I finally got my hands on a set of controls from Canada. These controls are exactly the same as the US ones, except set to display Centigrade instead of Fahrenheit. Before installing the CDM unit into my car, I took a high resolution picture of the bottom of the circuit board and I sat down and compared them carefully.

The scale used is determined by one jumper on the underside of the circuit board. I have confirmed this with a 72311AE11D and 72311AE08B. From what I can tell, the 11x are USDM and the 08x are CDM. The letter just indicates revision/year. Both of these types are made by Calsonic Kansei. Denso branded units are significantly different, but I have only seen that brand on JDM units but there may be Denso ones in the US as well. This modification is not for Denso units, only for Calsonic units.

The conversion is extremely simple, one jumper wire in the R145 position. I have two pictures indicating where it is on the board.

https://sl-i.net/FORUM/images/imported/2013/02/IMAG0124_zpsdd29fe76-1.jpg

Closer shot:
https://sl-i.net/FORUM/images/imported/2013/02/IMAG0123_zps1ecf2b40-1.jpg

Simply solder a wire across the two pads, and voila... Metric readout!

https://sl-i.net/FORUM/images/imported/2013/02/IMAG0122_zpsc40eabcc-1.jpg

[Yamazaki]

It's really that simple?! Wow, thank you! Once again, you demonstrate your electrical god-like powers...

[Dead91silvia]

Sooo.... I'm wondering how hard it would be to change my GT-B to Fahrenheit... ?

[amgarrety]

That is amazingly simple! Well, from a "doing" stand point anyway. It would've taken me much longer to actually find what out what I need to do to convert it, which I assumed was impossible.

Thanks for this!

[rkrenicki]

Sooo.... I'm wondering how hard it would be to change my GT-B to Fahrenheit... ?

Probably not. The Auto HVAC for 2nd gen was never used in the US on any model, so there are likely no provisions in its software for both.

The only way this one works is that they used the same module for Canada, so the software was written to do both and selected by a hardware jumper. It is very likely that the 3rd gen JDM ones would not be able to be modified to Fahrenheit either.

I could poke around the 3rd gen JDM ones that I have, because even if I blow one up, I do have two of them.. hah

[Dead91silvia]

Bummer... I guess I will learn C then... haha

[rkrenicki]

A good place to start is 22.0c which is about 72f. For real simple math, each degree up or down from there is "about" 2f, so 21c is about 70f, 23c is about 74f.. etc

[rkrenicki]

I have confirmed that this is switchable even when on. If you were to wire a switch to each side of that resistor pad, you can switch between F and C at will.

Here is a video of me connecting and disconnecting while on, I did not have a switch handy so I just pressed the wires together.
http://krenicki.com/ForumPictures/Technical/Modifications/th_MVI_2482_zps4b820b39.jpg (http://krenicki.com/ForumPictures/Technical/Modifications/MVI_2482_zps4b820b39.mp4)

[boglin5000]

Did you mod the digital display to be teal instead of green, or is it just your camera?

[rkrenicki]

It is just my camera. The display is still very much green.

[boglin5000]

It is just my camera. The display is still very much green.

Darn it. I am going to have to do the color shift with cellophane then. :smt013
Thanks for the quick reply!

[dodik]

You are the man I've been trying to do this for like 6 years.
ps display is actually white its just the lens is painted green, pull glass of and you shall see

[rkrenicki]

The display itself is a standard Vacuum Fluorescent Display, which would be a light blue, like what used to be in VCRs, Tape Decks and CD Players back in the day. It was common to put a green plastic filter infront of them to make them display green like what was done here. Putting another color cellophane between this would be whatever color you put in mixed with a little bit of blue and the green that the front plastic is made of.

[dodik]

when I pilled off the glass mine was white not blue, but then again there are maybe different units, I have to check what brand I have.

[rkrenicki]

Well, a very very light blue.. near white. VFDs technology has not really changed much in the 50 years or so since they were invented, but they are all basically the same base color with some variation of light filters.