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Intro
First off, I want to start by noting that since this is my first how-to write up, I will be editing this as I go to make things better, so please feel free to criticize!

References
Thanks to Autozone.com schematics (create free account to browse other diagrams)
| Repair Guides | Instrument Panel, Gauges, & Console (2003) | Driver Information System Schematics | AutoZone.com

and Pennock's Fiero Forum post by Daniel

Digital Automatic HVAC install - Pennock's Fiero Forum

Disclaimer
As a disclaimer, I am not, and do not claim to be an expert in this field, and am not a certified mechanic.
Therefore, I cannot be responsible for any damage you do to your car and your first born child!
This is very complex procedure that involves removing some of the dash panels, soldering (please don't try to splice this many wires with crimp connectors, there I warned you!), running wires (I recommend using wire loom to make things look neat and then zip tie them to other wires), using a multimeter/continuity meter (if you follow the diagrams exactly you might not need to, but I recommend double checking everything), and general wiring and automotive know-how, so if you are a novice, never worked on your car, don't know what you are doing on this forum, or otherwise scared or incapable of performing the above tasks, please don't attempt this!

Leave a good solid couple of hours (or more if you haven't done much like this) to complete this! (you have been warned!)

I got my components from a local junkyard near me for under $50. I recommend also grabbing part of a engine wiring harness as cheap wire while you're there for the parts.

Parts List
Now that that's out of the way, here's the list of parts you will need (don't forget those connectors!!!):

1.Right and left temperature actuators (I know, the old manual ones look the exact same, but trust me, they WILL NOT work!)

2.Vacuum Solenoid Control Module and tubing (built in on the manual unit, you'll find this under passenger dash to the right of the blower motor. There are two screws holding it in place)
http://i.cubeupload.com/E2hkQk.jpg

3.HVAC Control Module Automatic (any years work)
http://i.cubeupload.com/jYX0l6.jpg

4.Sun load sensor and dash piece (center of dash by windshield. The middle "dome")
http://i.cubeupload.com/ftznWX.jpg

5. Inside air sensor (under driver's side floor to the right of the steering column attached to something)

6. Ambient Air sensor (inside passenger side bumper area)
http://i.cubeupload.com/qkfCtY.jpg

Wiring Charts
Here are the Wiring Charts for all the connectors (please read all notes)

http://i.cubeupload.com/3bIBs4.jpg
http://i.cubeupload.com/0MVtlC.jpg

I will be posting a video (and pictures) shortly showing the system in action as well as showing all of the components you need and how to remove them, so stay tuned!

Removal

1. Removing the dash face (move steering wheel all the way down, carefully pull towards you, unplug fog light switch, and remove piece).
Here's a good video showing up to radio removal: https://www.youtube.com/watch?v=nfSHJ3E0YRc

2. Remove the radio and hvac control modules (two 7mm screws on either side and unplug connector).

3. Remove the blower motor resistor (waaaaay in the back of the passenger floor behind blower motor held in by two bolts, rear is a slot so no need to fully remove) and disconnect.
Here's a video on a impala (same hvac system) that should help: https://www.youtube.com/watch?v=ySdLrL5IxyA

4. Remove left and right blend door actuators (either side behind the radio on driver's and passenger's side center wall held in by three screws) and unplug.
Here's a video on left side buick (similar to grand prix's): https://www.youtube.com/watch?v=QKdDTupYOCM
And here's the right side on monte carlo (almost identical removal proceedure): https://www.youtube.com/watch?v=mVP09M7hLB4

5. Remove middle sensors in center dash and remove old piece to make way for sunload sensor (the security light and light sensor twist 90 degrees and come out).

I then recommend simply cutting off the old plugs completely (the only ones you will need are from the old hvac control unit and the ones going to the blower motor) as not to confuse you and get in the way later), labeling the old hvac connector wires before cutting.

Installation
Simply follow the wiring charts posted above to run the wires to the components (installation is reverse of removal). (I will be posting detailed pictures shortly)

I recommend running them with separate wire looms branching from the main harness. In fact, if you measure, you can make most of these wiring harnesses on your work bench and then make the final connections in the vehicle to save you some frustration.

Once you have checked and double checked your wiring, plug everything in, connect the battery, turn on the ignition to accessory, and *****STOP****

Calibration
1. The automatic HVAC automatically calibrates it's temperature actuator positions after power has been disconnected, and so does the temperature sensor, so DO NOT TOUCH THE CONTROLS at this time!

2. If you do, you will have to pull the fuses for all systems, or disconnect the battery and try again.

3. After about 30 seconds or so, you'll hear the blower start to turn on and run, again, do not touch the controls (I know it's tempting!)

4. After about a full minute, everything should be calibrated, and you can now turn your car on and test (bi-lvl, recirc, heater, defrost are all vacuum actuated so they will not work without the car on)

5. And now, you can brag to all your friends that you have successfully installed automatic hvac in your car! Enjoy!

Notes
Note: a kit is "possible", but would still require you to remove the same components and install the new ones. If you get that far, I'm assuming going to the junk yard and soldering are no big deal. Plus, It'd be pricey for me to pull the parts, make the kit, and ship so.....

Contact
Feel free to PM me with any questions, but I prefer to respond on the forum so everyone can benefit! (no question is a stupid one!)
 
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