1986-1987 Saab 900 Temp Control: Diagnosing and Replacing the Finicky ACC Unit
This guide covers the common failures, diagnostic procedures, and replacement options for the Automatic Climate Control (ACC) unit in the classic 1986-1987 Saab 900.
- The ACC unit has a built-in self-diagnostic test; press 'AUTO' and 'VENT' together to get fault codes. An 'EU' code means the unit is bad.
- Compatibility is critical. This part fits 1986-1987 'Classic' 900s with specific VIN ranges (starts G2002126, G3002533, G7002883). Verify before buying.
- New units are not available, making a tested used OEM part the most practical and cost-effective solution.
- Common failures are due to internal electronic aging (solder joints, capacitors) and can sometimes be repaired by an electronics specialist.
Common Failure Symptoms
A failing ACC unit in a 1986-1987 Saab 900 can cause a variety of frustrating issues. Because the unit controls multiple functions, symptoms can seem unrelated, but often point back to this central controller.
- Unresponsive Controls: Buttons on the panel do not respond, or their function is intermittent.
- Blower Fan Stuck on One Speed: The fan may be stuck on the highest setting or not work at all, regardless of the fan speed selection.
- Incorrect Temperature Output: The system blows hot air when you want cold, or cold air when you want heat.
- Erratic Operation: The system may work correctly for a few minutes after starting the car, then begin to malfunction as it warms up.
- Flashing Display or No Display: The digital display on the unit may flash, show error codes, or go completely blank.
- Clicking Noises from the Dash: You may hear clicking from the unit itself or from the servo motors it controls as it struggles to adjust the blend doors.
How to Diagnose the ACC System
Before condemning the control unit, perform a few basic checks. First, inspect fuses #1 and #17 in the fuse panel, as these provide power to the ACC system. Also, ensure the battery voltage is stable and above 10 volts, as low voltage can cause strange electronic behavior.
Running the Built-in Diagnostic Test
The Saab ACC system from this era often includes a powerful self-diagnostic feature that can point you directly to the faulty component. While documentation for the 9000 is more common, the procedure is very similar for the 900's ACC I system.
- Turn the ignition key to the 'On' position. Running the engine is recommended to ensure stable voltage.
- Simultaneously press and hold the 'AUTO' and 'VENT' (the button showing an arrow pointing to the person's face) buttons.
- The unit should enter its diagnostic mode. The display may flash '88' as it runs a 30-40 second test, checking all its sensors and motors.
- When the test is complete, the number of faults found will appear on the left side of the display, and a fault code will appear on the right. If there are multiple faults, press 'VENT' to cycle through them.
Common fault codes include:
| Fault Code | Meaning | Possible Cause |
|---|---|---|
| 1C / 1U | Inside Temp Sensor | Sensor is shorted (C) or has an open circuit (U). |
| 2C / 2U | Outside Temp Sensor | Sensor is shorted (C) or has an open circuit (U). |
| 3C / 3U | Air Box Temp Sensor | Sensor is shorted (C) or has an open circuit (U). |
| 5C / 5U | Temperature Flap Motor | Motor is binding/jammed (C) or has an open circuit (U). |
| EU | Control Unit Internal Fault | The ACC unit itself has an internal failure and needs to be repaired or replaced. |
An 'EU' code is a strong indication that the control unit is the source of your problems.
Buying a Used 1986-1987 Saab 900 Temp Control
Since new OEM units are no longer available, the most common solution is to purchase a good used or remanufactured unit. This is often a better choice than trying to source cheap aftermarket alternatives, which do not exist for this specific, complex part.
Warning: Compatibility is specific and critical. This unit is for the 'Classic' Saab 900 body style equipped with Automatic Climate Control (ACC), not the manual heater controls. You must verify your vehicle's VIN. These units are known to be correct for chassis numbers beginning with G2002126, G3002533, or G7002883.
What to Inspect on a Used Unit
- Verify Part Numbers: Look for OEM part numbers 4070454, 9479841, or 9480641 on the unit's label. Sometimes a unit may have more than one number listed.
- Check the Connectors: Inspect the electrical connector ports for any signs of corrosion, bent pins, or heat damage.
- Look for Physical Damage: Check the plastic housing for cracks and ensure all mounting tabs are intact. Avoid units with signs of water intrusion or physical impact.
- Ask the Seller: Inquire if the unit was tested before being removed from the donor vehicle. A seller who can confirm it was working is preferable, as many failures are electronic and not visible.
Cost of Replacement
The cost to fix your climate control can vary significantly based on the path you choose. A used OEM part offers the best balance of cost and reliability.
| Part / Service | Estimated Cost | Notes |
|---|---|---|
| New OEM | Not Available | This part is discontinued by Saab. |
| New Aftermarket | Not Available | Complex, vehicle-specific electronics like this are generally not produced by the aftermarket. |
| Used OEM | $75 - $150 | The most common and cost-effective solution. Price depends on condition and seller. |
| Remanufactured | $60 - $200 | Specialty shops can test and rebuild your existing unit, replacing common failure components. |
| Shop Labor | $120 - $250 | Expect 1-2 hours of labor for a professional mechanic to access the dash and replace the unit. |
Replacement Guide Overview
Replacing the ACC unit is a manageable DIY job for those comfortable working inside a dashboard. The unit is located in the center console stack.
- Difficulty: 2.5 out of 5
- Estimated Time: 1 hour
General Steps:
- Disconnect the Battery: Always disconnect the negative battery terminal before working on vehicle electronics.
- Remove Surrounding Trim: You may need to carefully pry off trim pieces or remove adjacent switches to gain access. On some models, pushing the unit out from behind after removing a switch is an effective method.
- Disconnect Wiring: The main wiring harness has a connector that must be unlatched and swung away to be removed. There may also be a smaller secondary connector and vacuum lines.
- Remove the Unit: The unit is typically held in by clips or small screws. Once they are removed, it can be pulled from the dashboard.
- Installation: Installation is the reverse of removal. Ensure all electrical and vacuum connections are secure before reconnecting the battery and testing the system.
Known Issues, TSBs, and Recalls
There are no official NHTSA recalls or Technical Service Bulletins (TSBs) specifically for the Automatic Climate Control unit on the 1986-1987 Saab 900. Most issues are related to the age of the electronic components, such as dried-out capacitors and cracked solder joints on the internal circuit board, which fail after decades of heat cycles and vibration.
Pro Tip: If you are skilled with electronics, many of these units can be repaired. The most common failures are old solder joints that need to be reflowed or capacitors that have failed and need to be replaced. This can be a cheaper alternative to replacement if you have the right tools and experience.
Frequently Asked Questions (FAQ)
Why does my fan only blow on the highest speed?
This is a classic symptom of a failed blower motor resistor. However, in the Saab 900 ACC system, the fan speed control is integrated into the climate control unit. A fault code of 'AC' or 'AU' during the self-test would point to an issue in the fan control circuit or motor, which is managed by the ACC unit.
Can I use an ACC unit from a different year Saab 900?
No, it is not recommended. The units for 1986-1987 are specific, particularly concerning the VIN ranges. While units from other classic 900s may look identical, they can have different internal logic or vacuum porting, leading to improper function. Always match the part number and VIN application notes.
Can a bad ACC unit drain my car's battery?
Yes. If the control unit has an internal short or fails to shut down properly when the car is turned off, it can create a parasitic draw that will drain the battery over time. This is a known issue with failing electronic modules in cars of this era.
Is it hard to replace the bulbs inside the ACC unit?
Replacing the internal illumination bulbs is relatively easy once the unit is removed from the dash. The back cover can be removed, and the small bulbs are held in twist-lock holders. This is a good time to replace all of them, as the others are likely near the end of their life.
Technical Specifications
OEM Part Numbers: 4070454 9479841 9480641
Controls heating, A/C, and ventilation via electronic and vacuum-actuated controls. Features a self-diagnostic mode accessible via the control panel.
The information in this article is provided for general reference and educational purposes only. Vehicle specifications, procedures, and part compatibility can vary by production date, trim level, and region. Always consult your vehicle's factory service manual and verify part numbers before purchasing or performing repairs. Safety-critical components such as airbags, seat belts, and braking systems should be installed by a qualified professional.
- Saab 900: