AC High Pressure Switch

This procedure covers the replacement of the AC high pressure switch on a 2007 Ram 3500 with the 5.9L Cummins diesel engine.

Warnings

Tools required

Parts

• AC high pressure switch × 1 — Use OEM specification
• AC line O-ring set (if damaged) × 1 — Use OEM specification

Fluids

• R-134a

Preparation

1. Park vehicle on level surface and engage parking brake
2. Allow engine to cool completely if recently operated
3. Ensure AC recovery equipment is certified and functioning properly
4. Verify you have the correct replacement switch for your vehicle

Procedure

1. 1

   Recover AC refrigerant
   Connect the AC recovery machine to the service ports. Follow the recovery machine manufacturer's instructions to completely evacuate all refrigerant from the system. Note the amount recovered for reference during recharge.
2. 2

   Locate the high pressure switch
   Open the hood and locate the high pressure switch on the AC discharge line. On the 2007 Ram 3500 with 5.9L Cummins, the switch is mounted on the high-side line near the condenser; verify the exact location and electrical connector configuration against the service manual for your vehicle.
3. 3

   Disconnect electrical connector
   Press the locking tab on the electrical connector and carefully pull it straight off the high pressure switch. Move the wiring harness aside to provide working clearance.
4. 4

   Remove the old switch
   Using an appropriate wrench, unscrew the high pressure switch from the AC line fitting. Turn counterclockwise to remove. Have a shop towel ready to catch any residual refrigerant oil that may drip from the port. Inspect the O-ring seal on the line fitting for damage.
5. 5

   Install new switch
   Check that the new switch has a proper O-ring installed. If the line fitting O-ring appears damaged, replace it with a new one from the O-ring set. Thread the new high pressure switch into the AC line fitting by hand first to ensure proper threading, then tighten snugly with a wrench. Do not overtighten as this can damage the switch or fitting.
6. 6

   Reconnect electrical connector
   Push the electrical connector firmly onto the new high pressure switch until it clicks into place. Verify the connector is fully seated and the locking tab is engaged.
7. 7

   Evacuate the AC system
   Connect the vacuum pump to the AC service ports using the manifold gauge set. Evacuate the system for a minimum of 30 minutes to remove all moisture and air. Monitor the gauges to ensure the system holds vacuum for at least 10 minutes after the pump is shut off, indicating no leaks.
8. 8

   Recharge the AC system
   Using the manifold gauge set, recharge the AC system with R-134a refrigerant to the specification on the underhood AC label. Add the same amount of refrigerant that was recovered, unless the underhood label specifies otherwise. Do not overcharge the system.

Reassembly

1. Verify all electrical connections are secure and properly seated
2. Ensure no tools or materials are left in the engine compartment
3. Close the hood after completing verification steps

Verification

• Start the engine and turn the AC to maximum cooling with the blower on high
• Allow the system to run for 5 minutes and verify the compressor engages
• Check that cold air is blowing from the vents
• Use a leak detector or soapy water solution to check the high pressure switch connection for leaks
• Verify proper system pressures using the manifold gauge set (high side should be 150-250 PSI depending on ambient temperature)
• Confirm the high pressure switch cutoff function is working by monitoring compressor cycling under normal operation

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