ACC 1 86-89 DIAGNOSTICS & TECH INFO

The first generation Automatic Climate Control system incorporates self diagnostic functions that require no special tools to access. If you notice a problem, you can place the control unit in diagnostic mode and it will find the problem for you.

Diagnostic Mode

To place the unit in diagnostic mode, turn the key on, running the engine is recommended to insure adequate battery voltage for the approximately 40 sec test, and push the AUTO and VENT buttons simultaneously. The unit will begin to flash 88 in its display and will run through a program and measure all its parameters. When it is finished, it will display a number corresponding to the number of codes present.

Code Access

After the ECU shows you the number of codes, pressing VENT will display the actual code. Pressing any button or AUTO will exit the diagnostic mode and return to normal operation. If more than one code is present, continue to press VENT until all codes are displayed. Record them as they appear.

Fault Codes

INVOLVED COMPONENT'S POSSIBLE PROBLEM

1C Inside Temp Sensor Shorted
1U Inside Temp Sensor Open
2C Outside Temp Sensor Shorted
2U Outside Temp Sensor Open
3C Air box Temp Sensor Shorted
3U Air box Temp Sensor Open
5C Motor for Temp Flap Binding or jammed
5U Motor for Temp Flap Open
6C Motor for Air Drum Binding or jammed
6U Motor for Air Drum Open
7C Motor for Recirc Flap Binding or jammed or shorted
7U Motor for Recirc Flap Open
AC Fan Speed Control Short to ground or open
AU Fan Motor or Controller Open
EU Control Unit Internal fault, replace unit

COMMON PROCEDURES FOR ALL CODES AND PRECAUTIONS

Check the power and ground to the ACC unit. The unit gets power from fuses 1 and 17 in the glove box fuse panel. If one side of the fuse has voltage and the other doesn't, the fuse is blown. It is also a good idea to remove the fuse and make sure both of the pins it plugs into are secure in the fuse panel. If they loosen, they can push back and not contact the fuse. A test light or a voltmeter are good tools to use to check fuses. Measure the voltage across the battery terminals first to give yourself a reference of available voltage. Anywhere in the diagnostic steps that battery voltage is mentioned, the reading across the terminals will be the reading you are looking for. Strange things happen when the battery voltage drops below 10V DC. If battery voltage is below this threshold, recharge or replace the battery prior to any further testing. If the engine is running, the battery voltage will increase, but should not exceed 14.6V DC.

You must carefully read the instructions as to whether the control unit is plugged in to its connector or not when taking voltage or resistance readings. Failure to do so can cause either misdiagnosis or worse, damage to components. It is a good practice to make sure the key is off before disconnecting the control unit.

Look at any disconnected connector for any corrosion. Spraying each with a contact cleaner is a good idea.

Fuse 17 should have battery voltage all the time, key on or off. (+30 supply)

Fuse 1 should have battery voltage any time the key is on or the engine is running. (+54 supply)

Fuse 18 is the main supply for the Rear Window defrost Battery voltage should be present here all the time (+30)

Fuse 6 is the supply for the fan motor. It should have battery voltage anytime the key is on or engine running (+54)

To remove the control unit from the dash to carry out tests is an easy affair. Take out the ashtray as though you were going to empty it, reach in behind the ACC control unit and push it out.

The following tests are carried out at the back of the control unit with the control unit disconnected from its 25 pin connector. Try to leave the single black wire connected to the unit at all times. It will prevent damage to the electronics from static electricity discharges. Take all readings from the back of the connector pins, where the wire comes in, not the side that actually plugs into the control unit. This prevents spreading of the pins and possible problems from poor connections. Close inspection of the connector will reveal pin numbers molded into the plastic on the back side of it. Where ever possible, wire colors will also be given in the instructions.

Power from fuse 17 comes into the unit on pin 1 of the connector (Red wire # 620 1.5 mm) You should have battery voltage here at all times regardless of key position. Attach negative lead of meter set to 12V dc scale to a good ground, metal in the dash or the metal of the ignition key works well as does the latch on the B pillar for the door. Touch positive lead of meter to pin and read voltage.

Power with the key on or engine running comes in from fuse 1 on pin 14 (green wire # 621 1.5 mm) Attach meter as above except put positive lead on pin 14.

Power to the lights in the control unit comes from the rheostat wheel on the left side of the dash on pin 18 (brown and white wire # 610 0.5 mm). When the rheostat is set to low illumination, no voltage should be present. When is set to bright illumination, battery voltage should be present. Connect meter as above except with positive lead on pin 18.

Ground for the control unit is on pin 13 (Black wire # 623 1.5 mm). Check this by reading voltage from pin 1(place Positive lead of meter here) and negative lead of meter on pin 13. Set meter to 12V dc scale. You should read battery voltage . This wire goes to the ground point in the fascia at the left front speaker.

After you confirm you have good ground and supply, you can do all further voltage checks by using pins 1 for power and pin 13 for ground. This makes it easier to connect the meter. But you have to confirm these pins first so no false readings will occur later.

Flap Position Motor

ACC 1 Wiring

Component Locations:

Code AU ACC I

With everything connected, check the power at pin 22 of the ACC control unit (The thing in the dash with the display) It will pop out by removing the ashtray, reaching in the hole and pushing the ACC unit out from behind. The voltage at pin 22 varies according to what speed is selected.

SPEED 1 .8V
SPEED 2 2V
SPEED 3 5V

As you select different speeds, the voltage should change. If these voltages aren't close and varying with different speeds, the control unit is bad.

If the readings are normal, disconnect the unit (turn key off first), check continuity between pin 22 of the control unit and pin 2(Blue wire) of the transistor unit (speed controller). The controller is located on the evaporator box, under the right plastic cover in the engine compartment near the windshield. Its connector on cars -88 is easily accessed by removing the cover, even though the actual controller lies deeper. There will be two similar connectors, one to the controller, one to the receiver drier pressure switch. On 88- cars the connector goes directly to the controller, there is no "pigtail" off the controller. You may have to remove the false bulkhead partition to get to the connector. One 12 mm bolt on the right side and one 25 Torx screw on the left side holds it down. It fits in a groove rather snugly and may take a bit of force to pull up. All the controllers sit down in the evaporator, held by four 10 Torx screws. They are black boxes about 4" X 4" in size.

The voltage measurement makes sure what the control unit tells the transistor, gets there. You check pin 2 of the transistor for the same readings you got at pin 22 of the control unit when changing the fan speed.

Pin 1(Green wire) at the transistor should be battery voltage with the key on. If not check fuse 6.

Jumping pins 3 and 4 of the transistor, with the transistor disconnected, should run the fan. If the fan runs, the transistor is bad. If it doesn't, go directly to the fan connector under the center and left covers. It should receive voltage when the key is on. If not, check fuse 6. If the fan has power and you ground its ground pin directly, and it runs, you have a wiring problem between the controller and the fan on the ground circuit. If not, the fan is bad. Make sure you are checking the fan wires, not the air box temperature sensor. The temp sensor has red wires, the fan a green wire and a black wire, both of larger gauge than the temp sensor.

Code 1C & 1U

Code 2C & 2U

Code 3C & 3U

The following is the factory training manual test procedure for code 3A,3U in the ACC I variant.

Remove the ashtray, reach in and push out the ACC control panel. With the key off, unplug its connector. With an ohmmeter, check resistance across pins 4 and 25. You should have 2000 -17000 ohms with the ACC set to LO. You should have 790-2000 ohms with it set to high allow temp stabilization time after moving temp setting and turn key off each time before plugging/unplugging the control panel to take resistance readings

Now for my experiences with this code. I like to try and find for myself why things fail and long ago found that the solder on the thin wires joining them to the pins is weak. After I discovered this, I have been able to successfully repair all the ones with this code. The resistors wiring is broken and you will get an open circuit reading from pins 4 and 25. Remove the glove box and the sensor plugs into the air box in the center of the car on the right side lower aspect of the air distribution box. Doing the resistance test from the control panel's connector will verify the wiring as well as the sensor. If you get an open, first check the wires for continuity never seen a problem here though). Unplug the sensor and check each wire for resistance between its ends. It has two wires, violet and black on its connector. Extract the sensor from the air box and unplug it. Open up its white plastic case held with interlocking tabs) and look at its thin wires, usually one of them has come unsoldered. You can carefully resolder it and restore its function. I have fixed many this way. I have no idea what a new one costs, I've never had to replace one, just fixed the old ones. You might also want to strengthen the other solder joint there with a little more solder so it doesn't let loose in the future while you have it out. Takes about 20 minutes start to finish. Put everything back together and rerun the self diagnostics, code should be gone

Code 3C & 3U

Code 5C & 5U

Code 6C & 6U

Code 7C & 7U

Defrost and Heated Mirrors