AC Compressor

Complete removal and replacement of the AC compressor on a 2019 Mercedes-Benz G-Class with 4.0L Turbo V8 engine, including refrigerant recovery, belt removal, and system recharge.

Warnings

Tools required

Parts

• AC compressor assembly × 1 — Use OEM specification (Mercedes-Benz part number A0008308900 or equivalent)
• AC line O-ring kit × 1 — Use OEM specification with R-1234yf compatibility
• PAG 46 oil (for compressor) × 1 — Mercedes-Benz approved PAG 46 synthetic
• Serpentine belt × 1 — Replace if worn or contaminated with oil

Fluids

• R-1234yf

Preparation

1. Park vehicle on level surface and engage parking brake. Allow engine to cool completely (minimum 2 hours).
2. Disconnect negative battery terminal and wait 10 minutes for system capacitors to discharge.
3. Recover all AC refrigerant using certified R-1234yf recovery machine. Record the amount recovered for recharge reference.
4. Measure and record PAG oil recovered during refrigerant recovery process.
5. Remove engine cover by pulling upward on front clips and lifting away from rear mounting grommets.
6. Remove front underbody splash shield to improve access to compressor lower mounting area (secured by approximately 8-10 plastic clips and Torx fasteners).

Procedure

1. 1

   Remove serpentine belt
   Locate the automatic belt tensioner on the front of the engine (right side, above compressor). Using a serpentine belt tool or 1/2" breaker bar, rotate the tensioner clockwise to release belt tension. Slip the belt off the AC compressor pulley first, then release tensioner slowly. Remove belt from all remaining pulleys and extract from engine bay. Inspect belt for oil contamination or damage - replace if contaminated by compressor seal failure.
2. 2

   Disconnect AC compressor electrical connector
   Locate the electrical connector on the rear of the compressor clutch assembly. Press the locking tab and pull the connector straight off. If connector is difficult to access, it may be necessary to disconnect the wiring harness bracket from the engine block for additional slack.
3. 3

   Disconnect AC refrigerant lines from compressor
   Position drain pan beneath compressor to catch residual oil. The compressor has two refrigerant line connections: discharge line (high pressure, smaller diameter) on top and suction line (low pressure, larger diameter) on the side. Both connections use bolt-type fittings. Remove the mounting bolts for each line (typically 10mm heads or Torx). Separate the lines from the compressor and immediately cap all openings with clean plastic plugs or tape to prevent moisture and debris entry. Note the orientation and condition of the O-rings for reference.
   ⚠Even after refrigerant recovery, residual oil may drain from lines. Keep drain pan in position.
4. 4

   Remove compressor mounting bolts
   The AC compressor is secured to the engine block/front accessory drive bracket with 3 mounting bolts. Access the bolts from above and below the compressor. Remove all 3 bolts completely and set aside. The front lower bolt may require extension and universal joint for access. Support the compressor weight while removing the final bolt.
5. 5

   Remove AC compressor from vehicle
   With all bolts removed, carefully maneuver the compressor out of the mounting bracket. The compressor must be tilted and rotated to clear surrounding components (alternator, power steering reservoir, engine mount). Remove compressor from engine bay and drain any remaining oil into a graduated container. Measure and record the amount of oil drained - this will determine the oil charge for the new compressor.
6. 6

   Prepare new AC compressor
   Remove shipping caps from new compressor ports. Check new compressor for correct oil level according to manufacturer specifications. Most new compressors come pre-filled with oil. Calculate total oil charge: if old compressor drained 90ml (3oz) and new compressor contains 120ml (4oz), drain approximately 30ml (1oz) from new compressor to maintain system oil balance. Alternatively, add the measured oil loss to the system during recharge. Add 15-30ml (0.5-1oz) of fresh PAG 46 oil to compensate for oil retained in old compressor and lines. Note: Compressor PAG oil (verify MB-approved viscosity — commonly PAG 100 for R-1234yf systems; confirm per compressor spec)
   ℹ️Excessive oil in AC system reduces cooling capacity and can damage compressor. Maintaining correct oil balance is critical.
7. 7

   Install new AC compressor into mounting position
   Maneuver the new compressor into the mounting bracket using the reverse path of removal. Align all three mounting holes with the bracket. Hand-thread all 3 mounting bolts to ensure proper alignment before tightening any bolt completely.
8. 8

   Torque compressor mounting bolts
   Torque the AC compressor mounting bolts in a cross-pattern to ensure even seating. Torque each bolt in two passes: first to approximately 12 Nm (9 lb-ft), then to final torque per MB specification (verify bolt count and final torque value in service data).
9. 9

   Install new O-rings on refrigerant lines
   Remove old O-rings from both refrigerant line fittings (discharge and suction). Clean the sealing surfaces thoroughly with a lint-free cloth. Inspect line fittings for damage or corrosion. Install new O-rings from the kit, ensuring they are properly seated in the grooves. Lightly coat new O-rings with fresh PAG 46 oil to aid installation and initial sealing.
10. 10

    Connect refrigerant lines to new compressor
    Remove protective caps from new compressor ports. Align the discharge line (smaller, high-pressure) to the top port and suction line (larger, low-pressure) to the side port. Ensure O-rings remain properly positioned during connection. Hand-thread the line mounting bolts first, ensuring threads engage smoothly without cross-threading. Once both lines are hand-tight, torque the mounting bolts to specification.
    Torque spec

    AC Line Fittings20 Nm (15 lb-ft)
11. 11

    Reconnect compressor electrical connector
    Push the electrical connector firmly onto the compressor clutch assembly until the locking tab clicks into place. Tug gently to verify secure connection. Re-secure any wiring harness brackets that were loosened for access.
12. 12

    Install serpentine belt
    Route the serpentine belt around all pulleys according to the belt routing diagram (typically shown on a decal on the radiator support or underside of hood). Leave the AC compressor pulley for last. Rotate the automatic tensioner clockwise with tool or breaker bar, slip the belt onto the AC compressor pulley, then slowly release tensioner. Verify belt is properly seated in all pulley grooves with no twists.
13. 13

    Evacuate and recharge AC system
    Connect R-1234yf recovery/recharge machine to vehicle service ports. Evacuate the system to 29+ inches Hg vacuum and hold for minimum 30 minutes to verify no leaks (vacuum should not drop more than 1 inch Hg). If vacuum holds, recharge the system to the factory-specified R-1234yf capacity shown on the underhood A/C label or service data (verify exact capacity for this vehicle). Add UV dye if desired for future leak detection. Start engine and activate AC system to circulate refrigerant.
    ⚠If system will not hold vacuum, there is a leak. Do not proceed with recharge until leak is located and repaired.

Reassembly

1. Reinstall front underbody splash shield with all clips and Torx fasteners.
2. Reinstall engine cover by seating rear grommets first, then pressing down firmly on front clips.
3. Reconnect negative battery terminal and torque to 8 Nm (6 lb-ft).
4. Clear any fault codes related to AC system using diagnostic scanner if available.

Verification

• Start engine and let idle for 2 minutes. Observe AC compressor clutch engagement when AC is activated - clutch should engage smoothly without noise or vibration.
• Set climate control to maximum cooling and lowest temperature. Verify cold air from vents within 2-3 minutes.
• Check center vent temperature with thermometer - should reach 38-42°F (3-6°C) at idle with ambient temperature of 70-80°F.
• Inspect all refrigerant line connections for signs of leakage (oil residue, bubbles if soapy water applied, or UV dye traces if used).
• Verify no unusual noises from compressor during operation (grinding, squealing, or rattling indicates internal damage).
• Check serpentine belt alignment and tension - belt should not slip or make noise during acceleration.
• Monitor AC system pressures if gauges available: typical running pressures are 30-50 psi low side and 200-275 psi high side at idle with 75-85°F ambient.
• Road test vehicle and verify AC performance under load. System should maintain cold air output during acceleration and at highway speeds.

Related trouble codes on this vehicle

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