AC Pressure Sensor

Replace the AC pressure sensor on a 2009 Aston Martin DB9 to restore proper AC system monitoring and function.

Warnings

Tools required

Parts

• AC pressure sensor × 1 — Use OEM specification
• AC pressure sensor O-ring × 1 — Use OEM specification

Fluids

• R-134a

Preparation

1. Park vehicle on level surface and apply parking brake
2. Turn ignition off and remove key
3. Allow engine and AC system to cool completely if recently operated
4. Verify AC system has not been recently serviced to avoid unnecessary refrigerant loss
5. Gather all tools and replacement parts before beginning

Procedure

1. 1

   Recover AC refrigerant
   Connect the appropriate AC recovery machine (verify refrigerant type on underhood AC label, typically R-134a for this model year) to vehicle AC service ports (low and high side). Follow recovery machine manufacturer instructions to safely recover all refrigerant from the system. Record the amount of refrigerant recovered for recharge quantity reference. Wait until recovery machine indicates system is fully evacuated. Note: Connect the AC recovery machine to the vehicle AC service ports (low and high side), using the refrigerant type specified on the under-hood AC label / OEM documentation (verify R-134a for this VIN). Follow recovery machine manufacturer instructions to safely recover all refrigerant from the system. Record the amount of refrigerant recovered for recharge quantity reference. Wait until recovery machine indicates system is fully evacuated. Note: Connect the appropriate refrigerant recovery machine (confirm refrigerant type via under-hood AC label — 2009 DB9 is typically R-134a) to vehicle AC service ports (low and high side).
2. 2

   Access engine bay AC components
   Open hood and secure with prop rod. The AC pressure sensor is located on the high-pressure AC line, typically near the condenser or receiver/drier (verify exact location against Aston Martin service documentation for the DB9). Use work light to identify the sensor, which is a small cylindrical component threaded into the AC line with a two-wire electrical connector. Note: The AC pressure sensor is located on the high-pressure (liquid) line of the AC system; confirm the exact location on this vehicle using OEM documentation before proceeding. Note: The AC pressure sensor is located on the high-pressure AC line near the condenser; verify exact location and side against Aston Martin service documentation before proceeding.
3. 3

   Disconnect sensor electrical connector
   Locate the electrical connector on the AC pressure sensor. Press the release tab on the connector and pull straight away from the sensor to disconnect. Do not pull on wires. Inspect connector terminals for corrosion or damage.
4. 4

   Remove AC pressure sensor
   Using the correct size wrench or socket for this sensor (verify hex size against OEM spec), loosen the AC pressure sensor by turning counterclockwise. Once loosened, unscrew by hand and remove sensor completely from the AC line fitting. Some residual refrigerant oil may drip; have a clean shop towel ready to catch any drips. Inspect the sensor port threads for damage. Note: Using the correct size wrench or socket for the sensor hex (verify the exact hex size against Aston Martin service documentation or by measuring the actual part before selecting a tool), loosen the AC pressure sensor by turning counterclockwise.
5. 5

   Prepare new sensor
   Remove new AC pressure sensor from packaging. Install the new O-ring onto the sensor, ensuring it seats properly in the O-ring groove. Apply a small amount of the OEM-specified clean refrigerant oil (verify PAG grade or other type per OEM spec) to the O-ring to aid installation and prevent damage during threading.
6. 6

   Install new AC pressure sensor
   Thread the new AC pressure sensor into the AC line fitting by hand, turning clockwise. Ensure threads engage smoothly without cross-threading. Once hand-tight, use the appropriate wrench to tighten the sensor to the manufacturer-specified torque (verify against Aston Martin service data — typically a low value for AC pressure sensors; do not assume). Do not overtighten as this can damage the fitting or sensor threads. Note: Once hand-tight, use the correct size wrench to tighten the sensor to the OEM-specified torque value (verify against factory documentation before tightening). Note: Once hand-tight, use the 19mm wrench to tighten the sensor to the manufacturer-specified torque (verify against Aston Martin service documentation; AC pressure sensors are typically 5-10 Nm / 4-7 lb-ft).
   Torque spec

   AC Line Fittings20 Nm (15 lb-ft)
7. 7

   Reconnect electrical connector
   Push the electrical connector onto the new AC pressure sensor until it clicks into place. Gently tug on the connector to verify it is fully seated and locked. Ensure no wires are pinched or routing near hot engine components.
8. 8

   Evacuate AC system
   Connect vacuum pump to AC service ports. Evacuate the AC system for a minimum of 45 minutes to remove all moisture and air. Monitor vacuum gauge to ensure system holds vacuum without decay, indicating no leaks are present. If vacuum decays, locate and repair leak before proceeding.
9. 9

   Recharge AC system
   Using the AC manifold gauge set and charging equipment, recharge the system with the manufacturer-specified weight of refrigerant per the underhood AC label or Aston Martin service data (reference the amount recovered in step 1 as a cross-check). Monitor low and high side pressures during charging. Add refrigerant slowly through the low-side port with engine running and AC on maximum cold setting. Note: recharge the system with the appropriate amount of R-134a refrigerant per the under-hood AC label / Aston Martin specification (reference the amount recovered in step 1 and confirm against the factory charge capacity)

Reassembly

1. Verify all electrical connections are secure and properly routed
2. Ensure no tools or parts are left in engine bay
3. Close hood securely

Verification

• Start engine and turn AC system to maximum cold setting
• Verify AC compressor clutch engages and system operates normally
• Check AC pressure readings on manifold gauges: low side should read 25-40 PSI at idle, high side should read 150-250 PSI depending on ambient temperature
• Inspect AC pressure sensor area for any refrigerant leaks (use electronic leak detector or soap solution)
• Verify AC blows cold air from vents and temperature control functions properly
• Use scan tool to verify no AC system diagnostic trouble codes are present and pressure sensor reading is within normal range

Related trouble codes on this vehicle

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