AC Low Pressure Switch

This procedure involves replacing the AC low pressure switch on the 2015-2020 Ford F-150 3.5L EcoBoost. The switch monitors refrigerant pressure and requires partial AC system evacuation.

Warnings

Tools required

Parts

• AC low pressure switch × 1 — Motorcraft SW-7359 or equivalent
• AC system O-rings × 2 — Use OEM specification
• R-134a refrigerant × 1 — Per system capacity
• PAG oil × 1 — PAG-46 per manufacturer specification

Preparation

1. Park vehicle on level surface and engage parking brake
2. Allow engine to cool completely if recently operated
3. Verify AC refrigerant recovery machine is functional and certified
4. Gather new O-rings and PAG oil before beginning work
5. Locate AC low pressure switch on suction line near accumulator on passenger side of engine bay

Procedure

1. 1

   Recover AC refrigerant
   Connect AC recovery machine to high and low side service ports. Follow machine instructions to completely recover all refrigerant from the system. Verify system pressure reaches 0 PSI on manifold gauges before proceeding.
   ⚠️System must be completely evacuated before disconnecting any AC components.
2. 2

   Disconnect electrical connector
   Locate the AC low pressure switch on the suction line near the accumulator. Press the locking tab on the electrical connector and pull straight out to disconnect. Inspect connector for corrosion or damage.
3. 3

   Remove low pressure switch
   Using appropriate wrench or socket, turn the low pressure switch counterclockwise to remove from the AC line port. Be prepared for small amount of residual oil to drain. Catch any oil with shop towel and measure for replacement quantity.
4. 4

   Inspect port and prepare new switch
   Inspect the AC line port threads for damage or debris. Clean port with clean shop towel if needed. Remove old O-ring from port. Install new O-ring on replacement low pressure switch and apply thin coat of PAG oil to O-ring.
   ⚠Use only new O-rings. Reusing old O-rings will cause refrigerant leaks.
5. 5

   Install new low pressure switch
   Thread new low pressure switch into AC line port by hand until finger-tight. Ensure switch threads smoothly without cross-threading. Tighten to specification using torque wrench.
   Torque spec

   AC Line Fittings20 Nm (15 lb-ft)
6. 6

   Reconnect electrical connector
   Push electrical connector onto new low pressure switch until locking tab clicks into place. Gently tug on connector to verify secure connection.
7. 7

   Evacuate AC system
   Connect AC vacuum pump to service ports. Evacuate system for minimum 30-45 minutes to remove all moisture and air. System should hold vacuum at 29 inches Hg for at least 10 minutes without loss to verify no leaks.
   ℹ️Proper evacuation is critical to prevent moisture contamination and ensure system longevity.
8. 8

   Recharge AC system
   Using AC manifold gauges and refrigerant canister, recharge system to manufacturer specified capacity. Add measured PAG oil that was lost during recovery (typically 1-2 oz for switch replacement). Monitor pressures during charging to ensure proper fill.

Reassembly

1. Verify all electrical connections are secure and properly locked
2. Inspect AC line fittings for any signs of refrigerant leaks
3. Ensure no tools or parts were left in engine compartment

Verification

• Start engine and turn AC to maximum cold setting with blower on high
• Verify AC compressor clutch engages and cycles normally
• Monitor AC pressures with manifold gauges: low side should be 25-45 PSI, high side 150-250 PSI at idle (varies with ambient temperature)
• Check for cold air from vents (vent temperature should be 35-45°F)
• Use electronic leak detector or soap solution to verify no leaks at low pressure switch connection
• Verify no warning lights or AC-related diagnostic codes are present
• Allow system to run for 10-15 minutes and recheck pressures and operation

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