Converting 2000 Legacy GT to Automatic Climate Control

[hupshall]

I'd like to start up a thread where we really figure out how to retrofit the automatic climate control system. For a lot of people, the cost / benefit ratio of this job will be well above their comfort zone. Expect to have to take the dash out and disassemble your AC system.

With that being said, I've spent a lot of time looking at the wiring diagrams for both the manual and automatic climate systems - From just the electronic components alone, These are the components listed for the Auto climate system:

Blower Motor Relay,
Blower Motor,
Blower Motor Resistor,
Ambient Temperature Sensor,
Evaporation Thermoswitch,
Air Mix Actuator,
Sunload Sensor,
In Vehicle Temperature Sensor,
fresh/Recirc Actuator,
Mode Actuator,
Auto A/C Control Panel.

Looking at part numbers, the Blower Motor Relay, Blower Motor, Fresh/Recirc actuator, and the Mode Actuator are the same units as what is already in the manual car - so, that means the new/additional components come down to:

Blower Motor Resistor,
Ambient Temperature Sensor,
Evaporation Thermoswitch,
Air Mix Actuator,
SunLoad Sensor,
In Vehicle Temperature Sensor.
A/C Control Panel.

Simplest way to get the wiring is to source an instrument and body harness from an Auto Climate equipped vehicle and strip the harness to it's just the climate subsystem.

To hook the wiring into an A/C car, we look at the wiring diagram and figure out how to get the AC panel all the required inputs.

Inputs needed from Manual harness

Auto A/C Control Module - Existing harness location & pin

A8 / FB-19 - i17 pin 8
A13 / FB-22 - i17 pin 14
B1 / FB-33 - Radio, i26 pin 6
B2 / FB-28 - Front Accessory, i24 pin 2

B3 / B88 Evaporation Thermoswitch Pin 3
B4 / B88 Evaporation Thermoswitch Pin 1
B5 - VSS
B10 - i17 pin 17
B14 - i17 pin 19
B15 - Vehicle Engine Temperature - B21, pin 10
B20 - i17 pin 18

Since the blower motor resistor is different, one possible way to branch into that circuit is to use the auto AC harness from the blower motor pin 2 and on

Some outstanding questions:

1) What EXACTLY does the air mix actuator do? Control Temperature? Are all the necessary fixings on the manual box? Basically, can you just install the servo and call it good or do you need to swap the whole assembly?
2) Where EXACTLY does the aspirator tube from the Automatic Climate control unit connect to? Does that socket exist on the manual box? (you will need this for accurate temperature readings)
3) The thermistors are different. The manual has a 3 wire thermistor, the automatic is a 2 wire - fine, but what exactly are the specs on these? Can the 3 wire be hooked up in such a way that the signal is the same as what the 2 wire sends to the control unit? If not, again, the box will have to be dismantled to gain access to the condenser.

I've not yet seen somebody successfully do this swap, let's figure it out - well, I want to figure it out anyway, and see exactly what needs to be done. That way, in the future, if somebody wants to go down this path, we'll somewhat know what needs to be done.

Also - for the sake of my discussion, let's stick with retrofitting the system into a H4 with the compressor which does NOT have the compressor speed pulse sensor, that's a circuit which is specific to the H6 ECU which we will not be using.

I'll add to this thread as I go along.

[Yamazaki]

Thank you for this thread. I wanted to do this a LONG time ago with my '00 GT ltd. But the task seemed too big and I sold the car to my brother so I could buy an H6 instead. I can't wait to see how you do it. One way to merge stuff might be to see how the H4 cars in Japan are configured with the auto HVAC. I would think that would be easier to merge with the North American H4 cars than the H6 ones.

[Dead91silvia]

I've thought about adding 3rd gen parts to my 2nd gen.... so this could be useful.

[rkrenicki]

Some outstanding questions:

1) What EXACTLY does the air mix actuator do? Control Temperature? Are all the necessary fixings on the manual box? Basically, can you just install the servo and call it good or do you need to swap the whole assembly?
Yes, it mixes the cold and warm air. I know that the servo has a linkage to the blending baffles, but I do not know for sure if the box itself is the same between both.


2) Where EXACTLY does the aspirator tube from the Automatic Climate control unit connect to? Does that socket exist on the manual box? (you will need this for accurate temperature readings)
It is a venturi tube that connects down to one of the air intakes. It is above the transmission tunnel on the drivers side footwell. With the air flowing through the HVAC air intake, it creates a very slight vacuum though the tube, that in turn pulls ambient air from the cabin across the temperature sensor in the controls. The venturi effect is extremely weak, and as such does not pull a significant amount of air across the sensor. This may not truly be needed.


3) The thermistors are different. The manual has a 3 wire thermistor, the automatic is a 2 wire - fine, but what exactly are the specs on these? Can the 3 wire be hooked up in such a way that the signal is the same as what the 2 wire sends to the control unit? If not, again, the box will have to be dismantled to gain access to the condenser.
I do not know about this one. I will check the Japanese HVAC boxes that I have in the closet to see how many wires are on its thermistor, but I do not know if that will be any bit of help to you.

[hupshall]

Rkrenicki, could you post a picture of the Japanese HVAC box showing the Air Mix Actuator? I know it's RHD but since it's sitting in the closet, it'll be easy to see and it may be close enough to how it mounts on a LHD box.

[hupshall]

So, I dug into the mechanism and function book and got some information about the Thermistors. In the manual AC controlled car, it's not actually a thermistor which you have access to at the 3 wire connector at B88 - it's actually a small circuit which controls the operation of the AC relay based on the thermistor temperature. Here is the diagram:

https://sl-i.net/FORUM/images/imported/2015/08/Manual20Thermistor-1.jpg (http://s1073.photobucket.com/user/hupshall/media/SLi/Manual%20Thermistor.jpg.html)

We need to see if the two wires to the actual thermistor itself are available through the module - Perhaps we can tie in there.

Specs on the thermistor that the Automatic AC unit wants to see:

https://sl-i.net/FORUM/images/imported/2015/08/thermistor1-1.jpg (http://s1073.photobucket.com/user/hupshall/media/SLi/thermistor1.jpg.html)

I still need to track down the specs for the manual thermistor, hopefully the resistance curve is the same.

Here is a picture of the manual AC Thermistor / Thermal control amplifier. You can see the two very narrow gauge wires going from the module into the HVAC unit - that is the connection to the thermistor. It may be possible to splice into those wires instead of having to remove and replace the thermistor assembly.

https://sl-i.net/FORUM/images/imported/2015/08/WP_20150804_002-1.jpg (http://s1073.photobucket.com/user/hupshall/media/SLi/WP_20150804_002.jpg.html)

[hupshall]

Rkrenicki kindly sent me a picture of the Automatic Climate Control Aspirator tube connection to the HVAC box, here it is on an Auto Climate system:

https://sl-i.net/FORUM/images/imported/2015/08/96AF91F0FB374B4880B4D5717F108761_zpsnzr6-1.jpg (http://s1073.photobucket.com/user/hupshall/media/SLi/96AF91F0-FB37-4B48-80B4-D5717F108761_zpsnzr6ve1r.jpg.html)

Here is the exact same place on my manual box:

https://sl-i.net/FORUM/images/imported/2015/08/WP_20150804_001-1.jpg (http://s1073.photobucket.com/user/hupshall/media/SLi/WP_20150804_001.jpg.html)

You can see that the casting is there - all that is required is CAREFUL drilling out of hole and installation of the white elbow - Part# 72128AC201

[rkrenicki]

The Japanese HVAC has a two-wire thermistor, just like the US Auto HVAC. I could take a picture, but it seemed relatively self explanatory. The thermistor itself is inside some black heat shrink, so there are no markings to read off.

[nepbug]

Some good info coming up in here. I thought about doing this and did some preliminary research a while ago, but then let it fade away as I'm pretty happy with the manual controls.

Hopefully you can keep the cluster temperature readout too, in the H6 cars it's solely on the autoclimate control unit.

[hupshall]

So I've been spending a little time examining the Thermistor assembly and the differences that exist between the manual AC cars and the ones that come with the automatic climate control equipped vehicles. The temperature/resistance curve for the automatic thermistor is included in the documentation & I have a link to it above. The manual thermistor has no documentation so I went to a wrecking yard and pulled a manual thermistor from a 2000 legacy. I hooked up the thermistor to my multimeter and made a plot of temperature vs resistance. That graph is here:

https://sl-i.net/FORUM/images/imported/2015/08/graph-1.jpg

I've made an f(x) function that based on a resistance value, it will give me the temperature:

double GetTemperature(double x) {
return 6.7736013883918787e+001 * pow(x,0)
+ -6.3220625305779770e+000 * pow(x,1)
+ 2.5259471296761021e-001 * pow(x,2)
+ -5.5556028940629328e-003 * pow(x,3)
+ 6.6480119323651939e-005 * pow(x,4)
+ -4.0634333312475662e-007 * pow(x,5)
+ 9.9178688341498114e-010 * pow(x,6);
}

So, now, based on the resistance given to me by the manual AC thermistor, I can calculate the temperature.

I also created another f(x) function which given the temperature, tell me what the resistance value should be for the automatic climate controlled vehicle. That function is this:

double CalculateResistance(double x) {
return 6.1365967365967382e+000 * pow(x,0)
+ -2.7183372183372168e-001 * pow(x,1)
+ 5.9090909090908916e-003 * pow(x,2)
+ -5.4856254856254554e-005 * pow(x,3);
}

So now, with these pieces, I can read the resistance value of the manual thermistor, do a little math, and figure out what the automatic thermistor would be reading at that same temperature.

I build a circuit using an ATMEGA328p and a Microchip MCP41010 digital pot which allows me to do just this.

Here is a picture of the circuit (prototyped) - I also have one multimeter hooked up to the automatic thermistor , and the other multimeter connected to the output of the 41010

https://sl-i.net/FORUM/images/imported/2015/08/20150829_221813-1.jpg

https://sl-i.net/FORUM/images/imported/2015/08/20150829_221759-1.jpg

https://sl-i.net/FORUM/images/imported/2015/08/resistor20data-1.jpg

So, based on this data, I should be able to send the automatic climate control head unit the data it expects and not have to disassemble the AC unit.

[Baja22]

I joined this forum just for this thread. I am definitely tagging along. If you need the electronic head unit I got one not knowing the complications with it. I be willing to donate!

[hupshall]

So I decided to make a complete harness from scratch, and for about half of the circuits, reuse the existing manual AC harness. I could have done this a few different ways but I decided to make a small harness which could plug into the connector already in my car (for the manual AC) and then branch those out to the auto unit. As you probably will end up finding out - I hate cutting into my cars factory harness, if I can branch in with connectors, I will do that instead.

I had a few adapter boards made up which would allow me to use the same connector as what is located in the manual AC climate control unit - TE Multi-Lock part# 175975-2

https://sl-i.net/FORUM/images/imported/2015/09/20150906_180221-1.jpg

https://sl-i.net/FORUM/images/imported/2015/09/20150906_180303-1.jpg

A Quick and dirty enclosure wraps keeps it safe, I'll wrap this in foam and secure it behind the dash:

https://sl-i.net/FORUM/images/imported/2015/09/20150906_180347-1.jpg

About half the circuits run through this:

https://sl-i.net/FORUM/images/imported/2015/09/20150906_180355-1.jpg

The rest of them I will have to do completely - I'm waiting for a few more boards so I can build my thermistor adapter so I can figure out a good wire length.

[rkrenicki]

I spy with my little eye... DorkbotPDX boards. It's been a while since I have used Laen for boards, but he does good work. :)


Sent from my iPhone using Tapatalk

[hupshall]

Ok, tonight I used a 1" hole saw & drilled out the opening for the venturi tube & installed it:

https://sl-i.net/FORUM/images/imported/2015/09/WP_20150925_001-2.jpg

[hupshall]

Quick Update, I have built my manual to automatic thermistor converter - it works great so I'll get it in an enclosure and keep on moving.

https://sl-i.net/FORUM/images/imported/2015/10/20150930_223801-1.jpg

[rkrenicki]

nice, a Digital Potentiometer.. you dont see those every day :)

[hupshall]

Update:

I have finished making the wiring harness and have started installing it into the car.

I re pinned the connector going to the blower resistor for the Auto AC (it's a 4 pin connector not a 6 pin) - pin 3 is not used, so the blue wire is unconnected:

https://sl-i.net/FORUM/images/imported/2015/10/WP_20151024_007-2.jpg

Sunload Sensor:

https://sl-i.net/FORUM/images/imported/2015/10/WP_20151024_001-2.jpg

This picture shows two things - The first, the plastic box on the left zip tied to the dash is my custom manual to automatic thermistor converter, you'll see that I cut into the black wires going into the heater box and added a connector so I could go back to manual easily if desired. The manual thermistor connector (yellow black box with VCC) - is still present, I gutted that and now it just acts as a way for me to tie into B88 without cutting or splicing.

https://sl-i.net/FORUM/images/imported/2015/10/WP_20151024_005-2.jpg

I have my Manual to Auto AC connector box zip tied to the dash support below the vents - the manual AC connector ties in here and allows me to reuse the existing harness to control all the servos that are common between manual and auto

https://sl-i.net/FORUM/images/imported/2015/10/WP_20151024_004-2.jpg

I have here just the auto module connectors:

https://sl-i.net/FORUM/images/imported/2015/10/WP_20151024_006-2.jpg

Next steps:

Finish up the ambient temperature sensor wiring to the front of the car - my car is a 2000 model year and does not come with that feature. I also have to install the air mix actuator, this is difficult since one of the screws is damn near impossible to get to...

https://sl-i.net/FORUM/images/imported/2015/10/WP_20151015_014-2.jpg

Almost ready to test.

[nepbug]

Great progress, waiting to hear test results

Sent from my VS985 4G using Tapatalk

[hupshall]

There are times when I want to find the engineer of something and smack them upside the head. Case in point on this project, the left rear screw on the air mix servo. I would *LOVE* to know what the Subaru repair schedule for this part is - it probably starts with "Remove heater assembly" or some such nonsense. I could not get a Phillips screwdriver up and into position to be able to install that screw. What I ended up doing was finding a button head self tapping Allen screw and using a ball head Allen wrench - moving the screw about a quarter of a turn at a time. It took me a little while but it is now secure. To aid in the positioning and installation of the screw, I first attached it to the servo and partially screwed it into a fiber washer which held it in place.

Screw:

https://sl-i.net/FORUM/images/imported/2015/10/WP_20151030_011-2.jpg

In place with washer:

https://sl-i.net/FORUM/images/imported/2015/10/WP_20151015_013-2.jpg

When removing the manual controls, you need to remove the actual plastic lever which operates the air mix door in the heater itself, it's very easy to remove - I just placed a flat head screwdriver between the base of the lever and the heater core - and then twisted the screwdriver.

Manual one:

https://sl-i.net/FORUM/images/imported/2015/10/WP_20151015_006-1.jpg

Automatic one:

https://sl-i.net/FORUM/images/imported/2015/10/WP_20151015_007-1.jpg

I put the ambient temperature sensor up on the front of the car, close to where the stock one went on later model year cars:

https://sl-i.net/FORUM/images/imported/2015/10/WP_20151030_009-2.jpg

Anyhow, everything is now connected, all the wiring is done so I thought I would test it out - Now, I know I didn't actually start the engine so I couldn't test if blew hot or cold - but the servos and blower motor all functioned as I would expect.
I'll be taking the car out of the garage soon and so I can really test everything then - but more than the dash is in pieces at the moment....

Here is a video:


https://youtu.be/3ELcdrmxCMw

[hupshall]

I had three circuit boards made for this project, they are available here:

https://oshpark.com/profiles/hupshall

[rkrenicki]

I wonder if taking the floor ducting out would have made that easier for the servo.. but that would require pulling the front carpet back, and possibly the front seats out. Might be easier to pull the dash at that point.

Have you actually buttoned it all back up and see if everything works? This is all very impressive, and I am glad that someone took the time to document it all. Also, do you have a running total for the cost of conversion?

[hupshall]

Here is the wiring diagram I used to build my harness:

http://i1073.photobucket.com/albums/w397/hupshall/SLi/auto%20climate%201.jpg

http://i1073.photobucket.com/albums/w397/hupshall/SLi/auto%20climate%202.jpg

http://i1073.photobucket.com/albums/w397/hupshall/SLi/auto%20climate%203.jpg

http://i1073.photobucket.com/albums/w397/hupshall/SLi/auto%20climate%204.jpg

[hupshall]

I've not yet put everything back together to see if it all works yet - It'll probably be a little bit before I can do that.

So, as for running total - I've not kept track - If I were to do it again, there are some things I bought that I wouldn't (wiring harnesses for example) - so let's figure it out:

Ambient Temperature Sensor w/ pigtail: $5 at the local pick n' pull
Misc pigtails used to build my wiring harness to connect to the servo's: $20 at the local pick n' pull
I spent some money at Mouser getting TE connectors for the sunload sensor - 174056-2 w/ associated pins - I bought a bunch of stuff along with it but probably $45-50 in connectors and pins
Sunload sensor came with some other bits and bobs I bought, but I've seen them on ebay for $20
Air Mix Actuator: $40.50 - Ebay
2004 Head Unit - No wear on buttons, $29.99 - Ebay, came with pigtails and in vehicle temp sensor
Probably close to $100 in custom electronics, enclosures, and wire.
Blower Motor Transistor - $30 - forums

So, what, approx $300?

I would say that if everything checks out once I start the car up - this was a fun project. Great to finally do it and dispel all those people who said it couldn't be done or was too difficult. Honestly, if you can read a wiring diagram and build a harness, you can do this conversion. I'd even go so far as to say you could just put in an automatic thermistor without even doing that arduino converter I built and just install it on the other side of the AC core - you have easy access to the core through the opening for the blower resistor. I bet that'd work just fine. If that was the case, honestly, the hardest thing was that darn back screw on the air mix servo!

[Yamazaki]

*slow clap*

....love it. Love all of it.

[digdug18]

And you're selling a complete kit for $400-$500?

[hupshall]

Uhh.. no. I've still not been able to start the engine to test the heater/cooler functions yet but even if everything checks out (which I have no doubt it will) - There is enough information on this thread for people to source the parts and do it themselves.

[hupshall]

Fired up the car and tested it today, everything worked - AC, heat, auto, defrost, etc - Done!

[Yamazaki]

Congratulations!

[nepbug]

Awesome, well done.

Sent from my VS985 4G using Tapatalk

[MannyMohawk#5]

Very impressive write-up. I wish I had this kind of technical knowledge when it comes to electronics.

[Dinka]

THIS IS GREAT!! Gonna Do this soon.

[duncanjb17]

very impressive write up. Thinking about doing this, if you were to do it again would you just use an automatic thermistor in place of the manual thermistor and forgo the converter you built?

[hupshall]

Yes, I would. I built the converter because I didn't want to disassemble the AC system. Well, I did a Turbo Conversion and all that stuff had to come out anyway so when I put it all back together, I used an automatic thermistor. In addition, you have easy access to the AC Evaporator core through the air filter door. You can just push an automatic thermistor into the AC core through that access point - using that and leaving the manual one in place. Just be sure you install it in a place that is not being rubbed on by the cabin filter (if you use one) - you could wear out the aluminum in the core (it's very thin) and create a leak.

[Romy]

I'm in the middle of doing this myself and found your thread. I'm swapping an STi motor in so had the harness all apart anyhow and just added in the Auto A/C stuff.

I'm wondering about the venturi tube that goes to the side of the heater core housing...are you positive there was a hole cut out on the auto a/c version? When I pulled mine from a junkyard I neglected to check...

I ask because I wonder if opening that hole up would cause false high readings (as it's connected to the footwell heat area)?

[Romy]

I think I'll answer my own question here... There's a k type thermocouple at the front panel of the Auto A/C unit. The airflow from the foot area flows through an annulus where the center section is connected to the front panel. So it basically acts like a venturi and creates a low pressure zone to make air flow past the thermocouple up top.

So hole saw it is :)

[rkrenicki]

I think I'll answer my own question here... There's a k type thermocouple at the front panel of the Auto A/C unit. The airflow from the foot area flows through an annulus where the center section is connected to the front panel. So it basically acts like a venturi and creates a low pressure zone to make air flow past the thermocouple up top.

So hole saw it is :)

Yep, that is correct. I didnt see your original question until now to answer it :)

[digdug18]

as soon as shit opens up again, I'm gonna hit up the junkyard and pull everything from an 2000-2004 outback llbean to see if I can make this work in my 99 outback.

[rkrenicki]

as soon as shit opens up again, I'm gonna hit up the junkyard and pull everything from an 2000-2004 outback llbean to see if I can make this work in my 99 outback.

It does not need to be an "LL Bean" model, but any H6 Outback.

It is also worth noting that the 3rd and 2nd gens are pretty different when it comes to the HVAC, I do not believe that fitting the 3rd gen parts into a 2nd gen will be easy to say the least.