AC Pressure Sensor

Replace the AC pressure sensor on the 2007-2013 Mercedes-Benz S65 AMG to restore proper AC system monitoring and operation.

Warnings

Tools required

Parts

• AC pressure sensor × 1 — A0045429018 or equivalent OEM
• AC line O-rings × 2 — Use OEM specification
• PAG oil (100 or 46 viscosity) × 1 — Use OEM specification

Preparation

1. Park vehicle on level surface and engage parking brake
2. Allow engine to cool completely for at least 2 hours
3. Ensure AC system has been off for at least 30 minutes to equalize pressure
4. Connect Star Diagnostic tool and document any existing fault codes
5. Locate AC pressure sensor on high-pressure line near firewall on passenger side of engine bay

Procedure

1. 1

   Recover AC refrigerant
   Connect AC recovery machine to service ports. Follow machine instructions to fully recover all R134a refrigerant from the system. Record amount recovered for recharge reference. Ensure system shows zero pressure on gauges before proceeding.
   ⚠️This step must be performed by EPA-certified technician. Venting refrigerant to atmosphere is illegal and environmentally harmful.
2. 2

   Disconnect battery negative terminal
   Disconnect negative battery terminal and wait 10 minutes for system capacitors to discharge. This prevents airbag deployment and electrical shorts during sensor removal.
3. 3

   Access AC pressure sensor
   Remove engine cover by lifting at front edge and pulling forward. The AC pressure sensor is mounted on the high-pressure AC line near the firewall on the passenger side, between the valve covers. May need to disconnect wiring harness clips for better access.
4. 4

   Disconnect sensor electrical connector
   Press release tab on electrical connector and carefully pull straight away from sensor. Inspect connector pins for corrosion or damage. Do not pull on wiring harness.
5. 5

   Remove AC pressure sensor
   Using appropriate socket, carefully unscrew AC pressure sensor from high-pressure line fitting. Turn counterclockwise. Some residual refrigerant or oil may escape. Catch any drips with shop towel. Inspect threads in line fitting for damage.
6. 6

   Prepare sensor port
   Inspect O-ring sealing surface on AC line for scratches, corrosion, or debris. Clean threads with lint-free cloth. Do not allow any dirt or debris to enter AC system. Keep port covered with clean cloth until new sensor installation.
   ⚠Any contamination entering the AC system can damage the compressor and cause expensive system failure.
7. 7

   Install new AC pressure sensor
   Apply thin film of clean PAG oil to new O-ring on replacement sensor. Thread sensor into high-pressure line by hand until finger-tight to ensure proper thread engagement. Use torque wrench to tighten to specification. Do not over-tighten as this can damage aluminum threads.
   Torque spec

   AC Line Fittings20 Nm (15 lb-ft)
8. 8

   Reconnect electrical connector
   Push electrical connector onto new sensor until release tab clicks into locked position. Gently tug connector to verify secure connection. Ensure wiring harness has adequate slack and is not stretched or pinched.
9. 9

   Evacuate AC system
   Connect vacuum pump to AC service ports. Evacuate system to at least 29 inches of mercury (98 kPa vacuum) and hold for minimum 30 minutes. System should hold vacuum without loss, indicating no leaks at sensor installation.
   ⚠If system will not hold vacuum, there is a leak. Do not proceed with recharge until leak is located and repaired.
10. 10

    Recharge AC system
    Recharge system with amount of R134a refrigerant documented during recovery step, typically 1400-1500g for S65 AMG. Follow recharge equipment instructions. Add PAG oil if significant amount was lost during recovery (typically 20-30ml if sensor was only component replaced).
11. 11

    Reconnect battery and clear codes
    Reconnect battery negative terminal. Using Star Diagnostic tool, clear any stored AC system fault codes. Start engine and allow to idle.
12. 12

    Test AC system operation
    With engine running, turn AC to maximum cold and fan to highest setting. Using Star Diagnostic tool, monitor AC pressure sensor readings. High-side pressure should be 150-250 psi with system stabilized. Check for proper compressor engagement and cold air output.

Reassembly

1. Reinstall engine cover by aligning rear tabs and pressing down at front until clips engage
2. Reconnect any wiring harness clips that were moved during access
3. Verify no tools or materials were left in engine bay

Verification

• Start engine and verify AC compressor engages when AC is activated
• Confirm cold air output from vents reaches appropriate temperature (40-45°F at vents)
• Using Star Diagnostic tool, verify AC pressure sensor provides live data readings within normal range
• Check for no fault codes related to AC pressure sensor or refrigerant pressure
• Visually inspect sensor installation point for any refrigerant oil leaks after 10 minutes of operation
• Verify AC system cycles properly and does not show pressure warnings on instrument cluster

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