AC Compressor

This procedure covers the removal and replacement of the AC compressor on the 2007-2013 Mercedes-Benz S65 AMG with the 6.0L V12 BiTurbo M275 engine, including refrigerant recovery, component removal, and system recharge.

Warnings

Tools required

Parts

• AC Compressor (Denso or OEM) × 1 — Use OEM specification
• AC compressor O-ring kit × 1 — Use OEM specification
• Serpentine belt (if damaged) × 1 — Use OEM specification
• PAG 46 compressor oil × 1 — Use manufacturer-specified amount
• R-134a refrigerant × 1 — System capacity approximately 1100-1300g

Preparation

1. Ensure engine is completely cool before beginning work
2. Park vehicle on level surface and engage parking brake
3. Disconnect negative battery terminal and wait 10 minutes for system capacitors to discharge
4. Raise and support front of vehicle securely on jack stands
5. Remove engine undertray panels to access compressor from below
6. Photograph serpentine belt routing before removal
7. Verify AC system has not been recently operated (system should be cool)

Procedure

1. 1

   Recover refrigerant from AC system
   Connect AC recovery machine to high and low side service ports. Follow machine instructions to completely recover all refrigerant from the system. Document the amount of refrigerant and oil recovered. The system should pull into a vacuum indicating complete recovery.
2. 2

   Remove serpentine belt
   Using serpentine belt tool, rotate tensioner clockwise to release tension. Remove belt from all pulleys starting with the AC compressor pulley. Inspect belt for wear, cracks, or glazing and replace if necessary.
3. 3

   Disconnect compressor electrical connector
   Locate the AC compressor clutch electrical connector on the front of the compressor. Press the locking tab and disconnect the connector. Remove connector bolt if equipped and move wiring harness aside.
   Torque spec

   Clutch Connector Bolt8 Nm (6 lb-ft)
4. 4

   Disconnect AC refrigerant lines
   Using line wrenches to prevent rounding, loosen and remove the high pressure and low pressure line fittings from the rear of the compressor. Cap all openings immediately with plastic caps or tape to prevent moisture entry and debris contamination. Note the location and orientation of O-rings.
   ⚠Even after recovery, residual refrigerant may be present. Work slowly and allow any remaining pressure to vent safely.
   Torque spec

   AC Line Fittings20 Nm (15 lb-ft)
5. 5

   Remove compressor mounting bolts
   From below the vehicle, locate the AC compressor mounting bolts (typically 3-4 bolts securing compressor to engine block bracket). Remove all mounting bolts while supporting the compressor weight. On the V12, access may require maneuvering around coolant hoses and power steering lines.
   ⚠Compressor weighs approximately 15-20 lbs. Support unit while removing final bolt to prevent dropping.
6. 6

   Remove AC compressor
   Carefully lower and maneuver the compressor out of the engine bay from below. The V12 engine bay is very tight—you may need to rotate the compressor and navigate around the frame rail, steering components, and coolant pipes. Work slowly to avoid damaging surrounding components.
7. 7

   Drain and measure old compressor oil
   Drain oil from old compressor into a graduated container by rotating the compressor shaft and pouring from the inlet/outlet ports. Measure the quantity of oil removed. This amount, plus any oil recovered by the AC machine, determines how much fresh PAG oil to add to the new compressor.
8. 8

   Prepare new AC compressor
   Remove shipping caps from new compressor. Check compressor oil level per manufacturer specifications—most new compressors come pre-filled. Adjust oil quantity based on amount removed from old compressor. Add fresh PAG 46 oil to the new compressor inlet port and rotate shaft 10 times to distribute oil internally. Install new O-rings on line fittings and lightly coat with PAG oil.
   ℹ️Use only PAG 46 oil specified for Mercedes-Benz AC systems. Wrong oil type can cause compressor failure.
9. 9

   Install new compressor
   Maneuver the new compressor into position from below, routing carefully around frame rails and other components. Align compressor with mounting bracket on engine block. Thread all mounting bolts by hand first to ensure proper alignment.
10. 10

    Torque compressor mounting bolts
    Torque the AC compressor mounting bolts in a cross pattern to ensure even seating. First torque all bolts to 10 Nm, then to final specification. Verify compressor is secure and properly aligned with belt pulley plane.
11. 11

    Connect refrigerant lines
    Remove caps from compressor ports and refrigerant lines. Verify new O-rings are in place and lightly coated with PAG oil. Thread line fittings by hand first to prevent cross-threading. Use line wrenches to torque fittings to specification—do not overtighten as this can damage O-rings and cause leaks.
    Torque spec

    AC Line Fittings20 Nm (15 lb-ft)
12. 12

    Reconnect electrical connector
    Reconnect the AC compressor clutch electrical connector until it clicks into place. Install connector bolt if equipped and torque to specification. Ensure wiring harness is routed away from hot exhaust components and moving parts.
    Torque spec

    Clutch Connector Bolt8 Nm (6 lb-ft)
13. 13

    Install serpentine belt
    Route serpentine belt around all pulleys according to routing diagram photographed earlier. Use belt tool to rotate tensioner clockwise and slip belt onto final pulley. Release tensioner slowly and verify belt is properly seated in all pulley grooves.
14. 14

    Evacuate and recharge AC system
    Connect vacuum pump to AC system and evacuate for minimum 45 minutes to remove all moisture and air. System should hold vacuum for 15 minutes without loss. Recharge system with correct amount of R-134a refrigerant (approximately 1100-1300g per system specification). Add UV dye if desired for future leak detection.

Reassembly

1. Reinstall engine undertray panels and torque fasteners
2. Reconnect negative battery terminal
3. Lower vehicle from jack stands

Verification

• Start engine and turn AC to maximum cold with fan on high
• Verify AC compressor clutch engages (audible click and pulley should spin)
• Check for cold air from vents within 2-3 minutes of operation
• Inspect all refrigerant line connections for leaks using leak detector or soap solution
• Monitor AC performance over 10-15 minutes—vent temperature should reach 40-45°F (4-7°C) at idle
• Verify system pressures are within specification using manifold gauges (typically 25-35 PSI low side, 200-250 PSI high side at idle, ambient 75°F)
• Check for abnormal noises from compressor during operation
• Verify serpentine belt is tracking properly on all pulleys without squealing

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