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Rebuilding ACC servos. Posted by Ari [Email]  (#2847) [Profile/Gallery]
(more from Ari) on Thu, 3 May 2001 08:52:44
In Reply to: acc fault codes, Daniel, Wed, 2 May 2001 16:58:27 Members do not see ads below this line. - Help Keep This Site Online - Signup |
Actually, that sounds like a problem in the servo. The servo is an electric motor with a big reducing gear train on it. It's very hard to backdrive a gear train, so you really shouldn't be able to turn the motor by hand in either direction.
First off, go to the Townsend site (http://www.townsendimports.com), and check out the technical data section. They have pages out of the Saab factory manual on troubleshooting the 6C and 7C faults. Sometimes the site is hard to get into, so I can't give you the complete path right now. But check under the ACC I technical documents.
Next, here is a post I did a few years ago on repairing and recalibrating the servo motors. I did it more out of curiosity than to save money. Since then, I simply picked up a set of servo motors from a junker and use them if a servo ever fails. All of the servos in the ACC (3 to be exact) are interchangeable.
Here's the old post:
#6881
3/29/96
Message from Ari Novis
Subject: Automatic Climate Control Fixes & Exhaust Parts Sources
==================
This post covers some ACC 1 topics (may or may not apply to ACC 2 - If
someone will give me a '92 turbo, I'll be glad to report on it):
-How to remove & install the air mixing and air distribution servos
-Possible fixes for fault codes 5 and 6
-Possible fixes for poor heat regulation
-Possible fix for no heat on your toes in the Floor position
Background - The heater core in the ACC1 system always gets hot coolant
flow. Cabin heat is controlled by the Air Mixing servo which combines hot
core air with cool outside/AC air. Air distribution (defroster, vent,
floor, etc.) is by the Air Distribution servo. Fault code 5 refers to the
Air Mixing servo, and code 6 is the Distribution servo. See posts 5509 and
4913 for ACC1 fault codes and how to run self test. Both servos are
mounted on a bracket accessible from behind the glove box.
I have found that the screws holding the servos to the bracket can loosen
up, causing the servos to flop around, providing poor control. This is
very easy to check by pulling the glove box, but you will have to remove
the bracket to tighten the screws.
The 5U or 6U fault code goes by the descriptive name of 'Other fault'.
This is usually an open in the wiring, a bad connection, or a short
circuit. Remove the cable from the connector on the bracket, and measure
(bracket side) with an ohm meter between pins 1 and 4, and 5 and 8 (motor
coils). A good motor is about 20 to 80 ohms. I had a shorted motor,
measuring 2 ohms. I was able to repair the motor by disassembling it, and
cleaning the brushes. Some people may just want to replace the motor.
The 5C or 6C fault code is 'Wrong direction'. This is useful if you have
reassembled the unit and it gives hot air when you call for cold, but if it
worked fine last week, why would it suddenly go bad? (I assume you don't
periodically rewire the car for practice). The servo measures position
with a potentiometer (variable resistor). The potentiometer has a
rotational range of about 300 degrees, but the servo uses only about 90
degrees. The ACC 1 controller gives a 'C' fault code if it reads a
position outside of normal, even if the servo is moving properly. If the
nylon gears driving the potentiometer slip, or the servo drives without the
mechanical stops on the bracket, the potentiometer can get out of alignment
with the servo. If this happens to the Mixing servo, heat control will be
poor. If it happens to the Distribution servo, settings at the stops will
be OK (defroster, vents), but the servo won't know where the intermediate
settings are (heat, floor, etc.). The servo must be re-calibrated or
replaced.
Procedures:
Remove the glove box: Four torx screws up by fuses, two at bottom. For
the bottom screws, I use a torx driver (socket? one of those inch long
things that snap on the end of a ratchet), so I don't have to remove the
glove box door. Pull the glove box out, being careful of the light and
light switch wires.
To access servo connector or remove servos: first remove the glove box.
Remove the two torx screws holding the fuse/relay panel and hinge it down.
The servo bracket is on the left, behind the center vents. The Mixing
servo has an arm with a cable running forward (to front of car). Turn the
car On (you don't have to start it). Changing the temp to Hi moves the arm
backwards. Play with the temp setting to get the arm back, but not against
the stop (the stop is some bent metal on the bracket). If it's on the
stop, you can't get to one of the mounting screws later. Select Defrost,
and wait for the servos to stop running. Hit Vent, wait 3 seconds, then
turn off the car. This puts the servos in a position for easy removal. Of
course, if you have a dead servo, you'll just have to wrestle it.
Remove the pressure clip holding the cable to the arm, and slip the cable
off. I looped a thread through the pressure clip so that when it flew off,
I could find it. Remove the two torx screws holding the bracket. Rock the
bracket slightly and pull back slowly. The bracket should slide out. To
install, you will have use a finger to align the white plastic doohickey
(technical term) to meet with the flat part of the Distribution servo arm.
This makes much more sense when you see it.
To re-calibrate a servo: Remove from bracket. The front of the servo is a
black plastic piece, rounded at the top, flat at the bottom, with the shaft
sticking out from the face. Remove the single screw in the middle of the
face, below the shaft. Carefully pry out the face. There is only one
loose gear, and no springs to fly out, so don't be afraid. The little gear
at the top corner drives the potentiometer. Remove the servo shaft and
gear, so the potentiometer can turn freely. The connector at the back of
the servo has five pins. Call the pins 1 through 5; it doesn't matter
starting from which side. Pins 1 and 5 are the motor coil, 2 and 4 the
ends of the potentiometer, and 3 is the potentiometer wiper. Measure the
resistance from pins 2 to 4 with an ohm meter. (I get about 4.4K). Measure
from pins 2 to 3, and rotate the potentiometer gear to get half the reading
from 2 to 4. (I set mine to 2.2K; you don't have to be exact 100 or 200
ohms off is OK). Put the shaft gear back in with the FLAT of the shaft
parallel to the flat part (bottom) of the servo. Put the plastic face back
on and check the resistance to make sure nothing moved.
Some (most?) people won't want to go through the hassle of rebuilding
servos. The servo bracket assembly can be removed in about 10 minutes very
easily, and the servos themselves are very simple to remove. Good luck!
---
I am looking to replace the leaking exhaust system on my 88 9000T -
everything aft of the catalytic converter - it's easier that way. Has
anyone recently gone through the task of calling around for the best price?
If so, please let me know the results of your search (with no more effort
than sending this post). I'm looking for the stock, plain vanilla system,
not a high performance boomer that will knock birds from the sky and send
children wailing to their mothers (adult care givers?)
Thanks,
Ari Novis
, Thu, 3 May 2001 08:52:44 <-- Viewing This Message, Fri, 4 May 2001 16:25:39
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