This procedure replaces the AC low pressure switch on a 2021-2024 Ford F-150 with 3.5L EcoBoost engine, which monitors refrigerant pressure and protects the compressor from low-pressure operation.

Warnings

Tools required

Parts

• AC low pressure switch × 1 — Use OEM specification
• AC line O-rings × 2 — Use OEM specification

Fluids

• R-134a or R-1234yf Refrigerant (as needed to replace lost during service)
• PAG 46 Oil (2-3ml for O-rings)

Preparation

1. Park vehicle on level surface and engage parking brake
2. Turn engine off and remove key from ignition
3. Allow engine compartment to cool to ambient temperature if recently operated
4. Open hood and secure with prop rod
5. Verify refrigerant type on underhood label (R-134a or R-1234yf)

Procedure

1. 1

   Recover AC refrigerant
   Connect AC recovery machine to both high and low pressure service ports. Follow machine manufacturer instructions to fully recover all refrigerant from the system. Record the amount of refrigerant and oil recovered for proper recharge amounts.
2. 2

   Locate AC low pressure switch
   The AC low pressure switch is located on the larger diameter AC line (suction line) running from the accumulator/dryer to the compressor. On the 3.5L EcoBoost, this is typically on the passenger side of the engine bay near the firewall. The switch threads directly into the AC line and has a 2-pin electrical connector.
3. 3

   Disconnect electrical connector
   Press the locking tab on the electrical connector and pull straight away from the AC low pressure switch. Do not pull on the wires. Move the connector aside to provide clearance for switch removal.
4. 4

   Remove old AC low pressure switch
   Using a 19mm wrench, turn the AC low pressure switch counterclockwise to unthread it from the AC line. Have a shop towel ready to catch any residual oil that may drain out. Remove the switch completely and inspect the sealing surface on the AC line for damage or debris.
5. 5

   Prepare new switch and O-rings
   Inspect the new AC low pressure switch O-ring. Apply a thin film of clean PAG oil (appropriate type for your refrigerant) to the O-ring. Wipe the threaded port on the AC line clean with a lint-free shop towel.
6. 6

   Install new AC low pressure switch
   Thread the new AC low pressure switch into the AC line by hand, turning clockwise until it seats. Ensure the switch threads in smoothly without cross-threading. Tighten the switch using a 19mm wrench to the specification for AC line fittings.
   Torque spec

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

   Reconnect electrical connector
   Push the electrical connector onto the new AC low pressure switch until the locking tab clicks into place. Verify the connection is secure by gently pulling on the connector body (not the wires).
8. 8

   Evacuate AC system
   Connect AC service machine to system service ports. Run a vacuum on the system for a minimum of 30 minutes to remove all air and moisture. The system should hold vacuum without loss for at least 10 minutes after vacuum pump is shut off. This verifies no leaks are present.
9. 9

   Recharge AC system
   Using the AC service machine, recharge the system with the correct type and amount of refrigerant as specified on the underhood label (typically R-1234yf for 2021-2024 F-150). Add the appropriate amount of PAG oil if any was lost during recovery. Follow service machine instructions for proper charging procedure.

Reassembly

1. Ensure all electrical connections are fully seated and locked
2. Verify no tools or shop towels are left in engine compartment
3. Close hood securely

Verification

• Start engine and turn AC to maximum cold setting with blower on high
• Allow system to run for 5 minutes and verify cold air output from vents
• With AC running, verify compressor clutch is engaged and cycling normally
• Use AC gauges to verify system pressures are within specification (typically 25-45 psi low side, 150-250 psi high side at idle, ambient dependent)
• Inspect AC low pressure switch area for signs of refrigerant leaks (oil residue)
• Turn off AC and engine, listen for any abnormal hissing sounds indicating leaks
• Use electronic leak detector around new switch installation if available

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