HVAC Problem: only full cold or hot air!
First what do we need?
For example a stupid mechanic who kills the battery for you (or it just starts from one day to the next).
There are several ways to fix this problem.
1. Calibrate the HVAC (copied from Saturn Sky Forum) Important: Do not adjust any controls on the HVAC control assembly during self-calibration. If interrupted, improper HVAC performance will result.
1) Turn ON the ignition with the engine OFF.
2) Turn the Temperature dial all the way to the right.
3) Turn the blower control dial all the way to the right.
4) Turn the mode position dial all the way to the left.
5) Simultaneously press and hold the A/C and Defrost buttons until the LED's start to flash.
6) Once the LED's stop flashing, calibration is complete. 2. Solder a resistor in the wiring harness (not my way to solve a problem / copied from Solstice Forum) Subject: HVAC Temperature Goes Full Hot When One Click Off Full Cold
Models: 2006-2008 Pontiac Solstice
2007-2008 Saturn Sky
Condition/Concern:
Some customers may complain that the temperature will go to full hot when they turn the temperature control one click off of full cold. The control head
is defaulting to Emergency Mode (this provides HOT air to clear the windshield in Defrost mode). This will happen if the feedback voltage for the air
temperature actuators are out of range.
Recommendation/Instructions:
Locally obtain a 60 to 68 ohm 1/2 watt resistor, and install it in-line in circuit 1688 pin F of the HVAC control head. Install the resistor just behind the
HVAC control head.3. Replace the blend door actuator (that's how I solved it) Needed tools and spare parts:
- ratchet
- finger ratchet
- nut driver with a 8 mm and 7 mm nut
- screwdriver bits
- new actuator / GM part number 10397365
- a lot of patience 
IMPORTANT! Adjust heating to full cold / all the way to the left!
First you need to remove the knee bolster (additionally I've removed the lower instrument panel) and fuse #10 on the floor console fuse block.
Then you'll need to figure out which is the damaged actuator (it's the left one, which is near the steering column, the right actuator is
for the air circulation).
Remove the screws by using the finger ratchet and a screw driver bit (I used the bit adapter on the screws which worked far better then using a bit /
trust me the screw fits into the adapter)
After working overhead (I still want to puke / problems with my sense of balance 
), breaking your hands, cutting your skin and scratching the
rocker panel including the sill plate (forgot the zipper on my pants), you'll be able to remove the actuator.
That has been the easy part and now we go on with the hard one, install the new actuator. 
Attach the wire on the new actuator, insert fuse #10, turn on the ignition and wait till the new actuator has moved to the full cold position.
Turn off the ignition and remove the fuse (additionally I have removed the wire, because I believe it's much easier to install the actuator without it).
Try to install the actuator, believe me it won't fit into place (even if you turned on the ignition and it has moved into the full cold position)
Don't touch the blend door, don't do it, never ever dare to think about moving it.
Moving the door will not solve the problem, it will make it worse.
If you set the HVAC to full cold before removing the damaged actuator, the blend door will be in the right position.
Unfortunately the new actuator (also the old one) will not fit on the screw positions (when the gear is in the hole of the blend door), but it's just about
a millimeter.
Push the gear in as far as possible, then gentile turn the actuator till you can insert the screws for thighten them.
Tighten the screws and insert the wire if you removed it.
Install the fuse.
Last but not least run the calibration.
The HVAC should work properly again.
Here is a little video from a Solstice owner:
https://youtu.be/Y77ME2LkkvEI hope this thread is useful!
