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OK, this is it. What we all have been wondering.

Can the rare, yet intriguing, electronically controlled automatic air conditioning system be retrofitted to a Legacy that is not so equipped? I'm certain the answer is yes, but I'm not sure how smooth the road is.

Let's start with an introduction of the various parts.

Of course we start with the control panel. This should simply bolt in to the same place as the original manual controls.

In the donor car, before teardown:


Assembly as installed in the car. The cup holder base/slider bolts to the bottom of the HVAC controller:


Manual controller on top, Electronic controller on bottom. Notice the locating pin on the rear of each:



The electrical connectors are not the same.

The manual controller has one connector with large wires (to carry the full current for the fan, white), and one connector with smaller pins (yellow) for the 'pushbutton' unit:


The automatic controller has two connectors (both black) that have small pins and carry all signals:


Some of you may be wondering how those small wires carry enough current for the fan. They don't. They carry a voltage "request" from the control unit to an amplifier (mounted in the A/C case) that controls the fan.



More to come......

This is called a Sun Load Sensor. It is used to let the control unit estimate the heat gain from the sun shining on all the windows. It replaces the leftmost trim piece at the end of the windshield defroster duct - the one that covers the dashboard mounting bolt:





This is the ambient temp sensor. It is used to measure the outside air temp. It is mounted to the hood latch riser behind the grill:






More to come..........

Dude your freaking awesome! Hope it goes as smooth as it can.

wow yea we definitely have all been waiting for this! the recirc option is worth it alone!

While the control panel is the most obvious change, there are many major and minor changes to the actual HVAC parts under the dash. The under-dash ductwork is actually three seperate parts.

The first part is the air intake and fan, marked as 1.
The second part is the AC evaporator. All air passes through it, and if the AC is turned on, gets chilled. Marked as 2.
The third part is the heater and air outlet doors. Marked as 3.

Believe it or not, most of the major components are the same or very similar. Most of the changed and added items are also noted in the diagram.



Part #1 is the air intake and fan unit. This appears to be the same basic housing as the manual AC system with the addition of a full speed relay for the fan and a unique intake door motor. Of course the mini-harness on the unit is specific to the automatic system.

Pics of the dirty as-pulled automatic AC intake/fan housing. Note the blue relay:





The door motor looks the same as the manual version and has the same part number (according to the manual posted on Josh's site). However, the wiring diagrams say differently. The Auto A/C has a 20% blend position while the manual version only has full inside air (max AC mode) or full outside air (all other modes). This will demand further investigation.

Manual:


Automatic:

PhyrraM, you're doing God's work here

Out of curiosity, is that a wagon? Based on the color, fuel gauge ticks, and radio I'm guessing it's a 91 LSi. I ask about the wagon because as I've discovered here only the 91 wagons had a rear intermittent wiper. I have the stalk installed courtesy of Mike, but it's looking like I need the rear intermittent wiper control unit. I don't have confirmation that it's in the wiper stalk like the front, but if it's not would you be willing to sell it from your donor car (assuming it's a 91 & wagon).

Thanks

Just saw this post and based on the VIN it's a sedan. Oh well.

It's a sedan. If you click on any of the pics, it should take you to my Flickr album that has a pic of the stalk.

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Didn't get much time this weekend so only a short, but quick, update.

Here is a pic of all three under dash units removed from the donor car.



From a quick examination it looks like the actual plastic boxes are exactly the same on both automatic and manual HVAC systems. It appears that the factory uses a common box assembly and then adds the proper (manual or automatic) actuators, sensors, clips, brackets, and wiring. Don't take this 100% yet, but it's beginning to look that way.

Hopefully more to come in the following week.....

Had a bit of spare time at work today ("It's good to be the boss"). Disassembled and cleaned the control unit.

A few notes:

The lights have blue caps and the light runners appear to be clear. I wonder what color the lettering appears to be on the unit - blue or green?

The temp up-down rocker uses a slightly bigger bulb than the rest of the control push buttons.

There are 6 LEDs on the push button panel. They are for the "on" indicators when a button is pushed or in use. All but "defrost" appear to be green, "defrost" appears to be yellow/amber.

There is a speaker or buzzer on the push button panel. I wonder if it's for errors or if the unit beeps on every key press.

A few of the buttons were just a tad sticky, that was the main reason for taking it completely apart. They cleaned up well and are now smooth again.

The temp display is a VFD. Again, I wonder what color it presents as.

Pics:

I'd assume it would light up green, to go with the stock dash and switch lights.

Keep this thread up to date, I've always been interested in the auto HVAC system and possibly swapping it in my cars.

I've disassembled the three under dash units and have started cleaning and restoring the components. I can verify that the air intake/blower housings are the same between auto and manual systems. I can also verify that the main heater/distribution housing is the same also. I cannot say 100% yet that the A/C condenser unit is.

The blower motor is the same between HVAC types. My donor unit is pretty well worn, as evidenced by the wear on the brushes and the commutator.


The replacement motor currently on the market do not have the Subaru plug and need to be spliced in. I will have to see how much a dealer wants for one.

A definite difference is how the blower is controlled. In cars with manual climate control, there are 4 fixed fan speeds determined by how the switch routes the power through a resistor network on it's way to the fan. On the automatic systems, the control unit sends a variable voltage signal to an amplifier wired to the fan. (yes, you can think of this just like an audio amp - small signal in, same, but louder, signal out). The amplifier is mounted in the evaporator case in the same spot that the resistor network normally goes.





The next thing I can confirm is that the mode door motor (the one near the drivers knee, that controls heat/vent/defrost) is also the same between auto and manual units. The air flow door positions are controlled by the arm position when the motor stops. Where the motor stops is controlled by a set of contacts attached to the gear that turns the actuator arm. Both manual and automatic motors have the exact same contact arrangement.



Auto on left:



The linkage arm is pressed onto the splined part of the shaft at the proper orientation to the contacts. By appling the power for the motor to a specific set of pins, the motor will stop with the arm at the desired angle. The linkages show above are adjusted to make sure the airflow doors are in the proper position for any given arm angle. This applies to both pushbutton manual systems and the automatic system.

Didn't you or someone say that with the auto HVAC unit there more positions that the mode door can be in? If that's the case and based on what you found with the mode door motors, the difference is in the electronics.

The above is for the mode/mix doors.

The difference I found is in the intake doors. The automatic system has a 20 percent fresh/80 percent recycled position that the pushbutton system doesn't. I haven't taken the intake door motors apart yet to look for differences.

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Oh ok, that's what I remember reading.

Thanks for the clarification.

The plastic housings nice and clean, fresh out of the dishwasher....





Next up, extracting all the relevant portions from the dashboard section of the harness:

That's a pretty good idea about the dishwasher!

I have the very same table and chairs.

Legacy777 wrote:That's a pretty good idea about the dishwasher!

I have the very same table and chairs.

Just don't let the wife see you do it......lol

Very true

Very quick update, unfortunately without pics.

I have traced, and compared to the wiring diagram, every HVAC related wire in the dashboard harness (and only the dash, so far). The quick and dirty observation is that it may be possible to convert to the automatic A/C system with A) the proper hardware (of course) and B) ONLY the dash harness and minor mods to the bulkhead harness and the engine compartment harness.

Most of the interconnects between the dash harness and the rest of the car seem to be the same as normal, pushbutton A/C cars.

In short, the major differences are:

1: The dashboard wiring harness
2: The "on unit" HVAC box wiring.
3: The control unit itself, of course.
4: The blend door (hot/cold) control. Cable on most cars, electronic motor on Auto Climate cars.

Some surprising things that are the same or very close:

1: All three HVAC "boxes". Only the evaporator is different to accommodate an extra temp sensor. (easy mod)
2: The air outlet mode and air inlet motors.
3: The underhood wiring, with the exception of two wires added for the ambient temp sensor.
4: So far - but subject to change - the Bulkhead harness is very close or even the same.


Random though....If the blend door motor and linkages, the fan amplifier, and a few other small things are the same as on an SVX, other Subaru (or even Nissan*), the only thing that would be hard to get (and Legacy specific) is the control panel itself as harness can be built by hand.

*Nissan and Subaru seemed to use common, or very close, electrical parts in the late 80s and early 90s. Not sure why.

I'm not ready to call this info 100% yet, but I know some of you that are following might want to know.


More to come......

Thanks for the update.

any news on that?
your thread inspired me to incorporate JDM RHD climate control into a LHD Legacy. After 2 years of research and a month of work here we go
and it's working!

Ben,

Do you have any pictures of the install? This looks really good!

Thanks Josh!

Yes I made some pics. Maybe some day I write the install story in a separate thread.