why does my BMW 3 Series E90/E91 (2005-2012) AC compressor run continuously?

BMW 3 Series E90/E91 (2005-2012)

Error Codes

2-4 hours

Time

medium

Difficulty

medium

Severity

3 min read

549 words

Problem Statement

The AC compressor in your BMW 3 Series E90/E91 (2005-2012) runs continuously, which may lead to potential system issues or decreased efficiency.

Estimated Time

2-4 hours

⚠️ Safety Warnings

Important safety information - read before proceeding

•Disconnect the battery before working on electrical components.
•Always wear safety goggles and gloves when handling refrigerants.

Symptoms

•AC compressor operates constantly without cycling off
•Unusual noise from the AC compressor
•Reduced cooling efficiency inside the cabin
•Increased engine load leading to poor fuel economy
•Possible refrigerant leaks or low refrigerant levels
•AC system not producing cold air as expected

Diagnostic Steps

1
Scan the vehicle's onboard diagnostics (OBD-II) for error codes related to the AC system.
2
Inspect the AC pressure switch for proper operation and continuity.
3
Check for refrigerant levels using a manifold gauge set.
4
Examine the AC clutch relay for function and correct wiring connections.
5
Inspect the AC control module for faults or stuck commands.
6
Verify the operation of the temperature control settings in the cabin.

Solution

💡 Expert Tip

For complex repairs like this, consider taking photos at each step. This helps if you need to reverse a step or consult with a mechanic. Also, keep all removed parts organized - you may need to reference them during reassembly.

Verification

After completing the repair, verify that the issue has been resolved:

✓Test the affected component to ensure it functions correctly
✓Check for any error codes or warning lights
✓Monitor the vehicle for a few days to ensure the issue does not recur

Prevention Tips

To prevent this issue from occurring again:

•Follow the manufacturer's recommended maintenance schedule
•Address warning signs early before they develop into major issues
•Use quality parts and fluids recommended for your vehicle
•Keep detailed records of all repairs and maintenance

Tools & Equipment Required

•OBD-II scanner
•Multimeter
•Manifold gauge set
•Socket set
•Torque wrench

Parts Required

•AC pressure switch (if faulty)
•AC clutch relay (if faulty)
•Refrigerant (R134a)

Related Faults

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Diagnostic Steps

1
Scan the vehicle's onboard diagnostics (OBD-II) for error codes related to the AC system.
2
Inspect the AC pressure switch for proper operation and continuity.
3
Check for refrigerant levels using a manifold gauge set.
4
Examine the AC clutch relay for function and correct wiring connections.
5
Inspect the AC control module for faults or stuck commands.
6
Verify the operation of the temperature control settings in the cabin.

Solution

1. Preparation

Gather all necessary tools and parts.
Disconnect the negative battery terminal to ensure safety while working on electrical components.
Wear safety goggles and gloves.

2. Inspect and Test AC Pressure Switch

Locate the AC pressure switch on the receiver-drier.
Disconnect the electrical connector from the pressure switch.
Use a multimeter to check for continuity across the switch terminals.
If the switch is faulty, replace it with a new one.

3. Check and Recharge Refrigerant

Connect the manifold gauge set to the low and high-pressure service ports.
Check the pressure readings against manufacturer specifications.
If refrigerant levels are low, recover the existing refrigerant, vacuum the system, and recharge it with the appropriate type and amount of refrigerant (R134a for this model).

4. Test AC Clutch Relay

Locate the AC clutch relay in the fuse box.
Remove the relay and test it with a multimeter to ensure it is functioning properly.
If defective, replace the relay.

5. Inspect AC Control Module

Access the AC control module, typically located behind the dashboard.
Check for any visible damage or loose connections.
Use a diagnostic scanner to check for any fault codes related to the AC system.
If the module is faulty, replace it with a new one and reprogram as necessary.