ACC blend door repair on a 1999 Saab 9-5.

If your air vents blow cold in the winter, or hot in the summer, if the A/C calibration shows error code 08 on the climate control display, then you probably have this problem. It's very common, especially on early 9-5s.

The climate control system has an air mixing flap on each side. They mix cold and hot air, so the temperature can be controlled separately on the driver and passenger side. Each flap is operated by a small stepping motor. The range of movement is limited by a short plastic stop arm. Its function is critical, because the mixing flap can cross its path with other moving parts if misaligned, and cause irreparable damage.

The ACC can detect when the stop arm is broken and stop the motor. Timely repair is important to prevent further damage. Don't put it off after the problem presented itself. A cracked stop arm or a broken shaft tip can be easily repaired. In more severe cases, the may snap inside the unit, which can only be fixed by removing the ACC module from the car and taking it apart, which is extremely labour intensive. There are various repair kits available from many online Saab parts retailers.

The only tools you need for the job is a pair of Torx and Phillips screwdrivers.

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Driver footwell

Undo the Torx screws holding the trim in the driver's footwell.
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OBD connector

Unscrew the OBD-II connector from the trim panel.
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Left motor

Locate the left stepping motor (it has a large "L" on it). Unplug the connector and any other wires in your way. Undo two screws holding the motor and pull it out.
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Shaft position

Make sure the notch on the shaft is pointed upwards. If it's not, plug the motor connector back in and run the ACC calibration until the shaft is positioned correctly.
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Broken arm

Old style green plastic stop arms often crack at the base, allowing the shaft to spin freely. Newer style white arms have this end reinforced, however they sometimes crack at the upper notch instead.
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Arm removed

Remove the stop arm. Inspect the yellow shaft, make sure it turns and is not broken. You can peek through the lower vent, or remove the vent completely for easier access to the inner part of the shaft.
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New vs old

This replacement arm was fabricated by my relative who works at the machine shop. It's made out of military grade aluminium, very light and strong. There are similar aftermarket replacement arms sold online.
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Alumimium arm

Install the new arm. It will be seated tight, so push it in carefully - all the way until the catch clicks. Before re-installing the motor, make sure the shaft profile is aligned with the notch on the motor shaft.
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Carpet clips

The passenger side is less prone to failure, but I decided to replace both as I had extra parts. Start by pulling the clips out of the carpet trim.
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Lower trim

Next, undo the four screws holding the lower plastic panel.
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Glovebox screws

Unscrew the lower edge of the glove box.
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Upper screws

Open the glovebox and undo the remaining screws along the top.
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Glovebox removed

Pull the glovebox, disconnect the vent hose and the electrical connector.
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Right motor

Locate the stepping motor with a large "R" on it, unhook the wires and unscrew the motor.
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Original arm

The passenger side arm is connected to a metal rod that operates additional vents on the floor.
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Arm removed

Unhook the rod and pull the stop arm off the shaft. Inspect for damage. My arm was starting to develop a crack at the upper notch.
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Rod fitting

Remove the soft plastic rod bushing from the old arm and insert it into the new arm.
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Installed

Installation is the reverse of removal. Once everything is done, start the car and run the ACC calibration by pressing AUTO+OFF.

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