1991-1995 Toyota MR2 Temp Control: Diagnosing Failures and Buying a Used Unit
This guide covers the common failures, symptoms, and replacement of the climate control unit in the SW20 Toyota MR2, with a focus on what to look for in a used part.
- The most common failure is internal electronics (capacitors, solder joints) due to age, leading to symptoms like a blinking A/C light or unresponsive buttons.
- Used OEM parts are the only viable option as new units are discontinued. Inspect connectors and ask the seller about testing before buying.
- Part numbers 55900-17110, 55900-17120, and 55900-17130 are generally interchangeable across the 1991-1995 model years.
- Replacement is a simple DIY job, requiring only basic tools and about an hour of time. The trickiest part is carefully disconnecting the mechanical control cables.
Symptoms of a Failing Temp Control Unit
When the climate control module in a 1991-1995 MR2 begins to fail, it can cause a range of frustrating issues. Because it's the electronic brain of the HVAC system, symptoms can sometimes be confusing. Here are the most common signs that your temp control unit is the source of the problem:
- Blinking A/C Light: This is a classic Toyota diagnostic signal. A blinking A/C light often indicates that the system's self-diagnostics have detected a fault. This could be related to the compressor, a sensor, or an internal fault within the control unit itself.
- Unresponsive Buttons or Sliders: You might press the A/C button or move the temperature slider with no effect. The buttons may feel normal, but the module fails to register the input and command the HVAC system.
- Fan Speed Issues: The blower fan may be stuck on one speed (often high), or you may not be able to adjust it at all. This points to a failure in the module's ability to communicate with the blower motor resistor.
- Incorrect Airflow Direction: You may try to direct air to the dash vents, only for it to come out of the floor or defrost vents. This happens when the module can no longer control the blend door actuators that direct airflow.
- No A/C Compressor Engagement: You press the A/C button, the light may or may not turn on, but the compressor clutch never engages. While this can be caused by other issues like low refrigerant, a faulty control unit can fail to send the engagement signal.
- Intermittent Backlighting: The illumination behind the buttons and symbols may flicker or fail to turn on, which can point to corrosion or bad solder joints on the circuit board.
Known Issues, TSBs, and Recalls
For a vehicle of this age, most issues are well-documented by the owner community rather than through official manufacturer channels.
- Common Internal Failures: The most common root cause of failure for these units is age-related degradation of electronic components. Dried-out capacitors and cracked solder joints on the main circuit board are frequent culprits. These failures can cause any of the symptoms listed above. Many owners with electronics experience opt to repair the board by re-soldering joints or replacing capacitors.
- Recalls: There are no specific recalls for the climate control unit itself. An early recall (NHTSA 91V223000) existed for the 1991-1992 MR2 concerning the occupant protection system, but it is unrelated to the HVAC controls. Another recall for 1991-1993 Toyotas was related to the A/C expansion valve, which could affect cooling performance but is not a fault of the control head.
- Technical Service Bulletins (TSBs): No specific TSBs for the 1991-1995 MR2 temp control unit were found in public databases. Any service bulletins would likely be outdated and superseded by general repair knowledge at this point.
Pro Tip: The blinking A/C light is a diagnostic tool. In many Toyota systems, it flashes a code that can be interpreted to pinpoint the problem. While not as advanced as modern OBD-II systems, it can help differentiate between a sensor issue and a control unit failure.
🎬 Watch this guide on diagnosing a flashing Toyota A/C lightBuying a Used 1991-1995 MR2 Temp Control
Since new OEM units are discontinued, a quality used part is the most common and practical solution. Here’s what to look for to ensure you get a good one.
Verify Part Numbers and Compatibility
The primary OEM part numbers for this generation are 55900-17110, 55900-17120, and 55900-17130. While they all fit the 1991-1995 model years, the later numbers represent revisions. Generally, these units are interchangeable. However, it is always best to match the part number from your original unit if possible. Part number 55900-17130 is listed as fitting the entire 1990-1995 range, suggesting it is a compatible replacement for earlier versions.
What to Inspect Before You Buy
- Physical Inspection: Check the casing for cracks or damage. Pay close attention to the mounting tabs to ensure they are intact for a secure installation.
- Connector Pins: Inspect the electrical connector ports on the back of the unit. Look for any signs of corrosion, bent pins, or melted plastic, which could indicate a more serious electrical issue in the vehicle it came from.
- Slider and Button Feel: The sliders should move smoothly without binding, and the buttons should have a positive click when pressed. A broken slider is a common issue, and 3D-printed replacements are available if you find a good unit with a bad slider.
- Ask the Seller: Ask if the unit was tested before removal. Inquire if the A/C light was blinking or if there were any known operational issues. A reputable seller should be able to provide this information.
Why Used OEM is the Best Choice
For a specialized electronic part like this, a used Original Equipment Manufacturer (OEM) unit is almost always superior to non-existent or poor-quality aftermarket alternatives. An OEM unit guarantees perfect fitment, correct electrical connections, and maintains the original interior aesthetics of your MR2. Given that the primary failure mode is electronic components aging, even a used unit may eventually require capacitor replacement, but it starts from a known-good design.
Cost of Replacing an MR2 Temp Control
The cost can vary significantly based on the path you choose. Here is an estimated breakdown:
| Part or Service | Estimated Cost |
|---|---|
| New OEM | $400+ (Discontinued/Very Rare) |
| New Aftermarket | Not Generally Available |
| Used OEM | $75 - $200 |
| Shop Labor | $100 - $200 |
Installation Guide (Difficulty: 2/5)
Replacing the temp control unit is a straightforward job that most DIY mechanics can handle with basic tools.
Estimated Time: 30-60 minutes
Tools Needed: Phillips screwdriver, trim removal tool (optional), small needle-nose pliers.
- Disconnect the Battery: Before working on any electronic components, disconnect the negative battery terminal.
- Remove Center Console Trim: The temp control is located in the center stack. You will need to carefully pry off the trim piece that surrounds the stereo and HVAC controls. 🎬 Watch how to remove the MR2 dash trim and A/C controls
- Unscrew the Unit: The control unit is typically held in place by four Phillips head screws. Remove these screws.
- Disconnect Electrical Connectors: Gently pull the unit forward. There will be two main electrical connectors on the back. Press the release tabs and pull them straight out.
- Disconnect Control Cables: There are also two mechanical cables that control the blend doors. These have small clips and loops that need to be carefully detached from the sides of the unit. Using needle-nose pliers can help release the clips.
- Installation: Installation is the reverse of removal. Connect the cables and electrical plugs to the new unit before screwing it back into place. Reconnect the battery and test all functions (fan speeds, vent modes, A/C) before re-installing the trim.
Warning: The mechanical control cables must be re-attached correctly. Before you begin, note the position of the levers on the old unit so you can match them on the new one.
Frequently Asked Questions (FAQ)
Why is my MR2's A/C light blinking?
A blinking A/C light is the car's way of telling you there's a fault in the climate control system. Common causes include a problem with the compressor clutch, a faulty pressure sensor, low refrigerant, or an internal failure of the temp control unit itself. It's a diagnostic signal that means the system has shut down to prevent further damage.
Can I repair my old temp control unit instead of replacing it?
Yes, repair is often possible for those with electronics and soldering skills. The most common failures are due to old capacitors on the circuit board failing. Replacing these capacitors can often restore full functionality to a dead or malfunctioning unit. You can find guides on forums like MR2OC.com that detail which capacitors to buy and how to replace them.
Are the temp control units from 1991-1992 and 1993-1995 MR2s different?
While there were several part number revisions (55900-17110, -17120, -17130), the units are physically and functionally interchangeable across the 1991-1995 model years. The later part numbers simply represent minor updates or a consolidation of previous parts. You can safely install a unit from a different year within this range.
My fan only works on the highest setting. Is that the temp control unit?
This specific symptom is more commonly caused by a failed blower motor resistor, not the temp control unit itself. The resistor is what controls the lower fan speeds. When it fails, the fan often defaults to the high setting, which bypasses the resistor. This is a separate, and typically cheaper, part to replace.
Helpful Videos
Technical Specifications
OEM Part Numbers: 55900-17110 55900-17120 55900-17130
Controls blower motor, A/C compressor clutch, and blend door actuators via electronic and mechanical outputs.
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.
- Toyota MR2:
- 🎬 Helpful Videos
- Symptoms of a Failing Temp Control Unit
- Known Issues, TSBs, and Recalls
- Buying a Used 1991-1995 MR2 Temp Control
- Verify Part Numbers and Compatibility
- What to Inspect Before You Buy
- Why Used OEM is the Best Choice
- Cost of Replacing an MR2 Temp Control
- Installation Guide (Difficulty: 2/5)
- Frequently Asked Questions (FAQ)
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