This procedure covers the removal and replacement of the air conditioning low pressure switch on a 1966 Chevrolet Corvette equipped with factory air conditioning.

Warnings

Tools required

Parts

• AC low pressure switch × 1 — Use OEM specification
• R-134a refrigerant (if converted) or R-12 refrigerant × 1 — Verify system type before purchase

Preparation

1. Park vehicle on level ground and engage parking brake
2. Turn off engine and allow vehicle to sit for at least 30 minutes if recently driven
3. Verify you have the correct replacement low pressure switch for your AC system type (R-12 or R-134a)
4. Locate the low pressure switch on the accumulator or low pressure line in the engine compartment, passenger side near firewall

Procedure

1. 1

   Recover refrigerant from AC system
   Connect the AC refrigerant recovery machine to the system's service ports. Follow the recovery machine's operating instructions to completely evacuate all refrigerant from the system into the recovery tank. Ensure the system pressure reads zero on the gauge before proceeding. This step must be performed by EPA-certified personnel with proper equipment.
2. 2

   Disconnect negative battery cable
   Disconnect the negative battery cable from the battery to prevent electrical shorts while working on the switch's electrical connector. Move the cable away from the battery terminal.
3. 3

   Disconnect electrical connector
   Locate the electrical connector on the low pressure switch. Carefully pull the connector straight off the switch terminal. If corrosion is present, gently wiggle while pulling. Do not pull on the wires themselves.
4. 4

   Remove low pressure switch
   Using an appropriate line wrench, turn the low pressure switch counterclockwise to unthread it from the receiver-drier or line fitting. Verify the correct hex size for your specific switch before applying a wrench. Once loose, remove by hand and set aside. A small amount of residual oil may drip from the port.
5. 5

   Inspect O-ring and sealing surface
   Examine the O-ring on the new switch and the sealing surface on the receiver-drier or line fitting. Clean the fitting threads and sealing surface with a clean shop towel. Ensure no debris or old O-ring material remains on the threads.
6. 6

   Install new low pressure switch
   Thread the new low pressure switch into the receiver-drier or line fitting by hand, turning clockwise. Once hand-tight, use the wrench to snug the switch. Tighten until the switch seats firmly against the O-ring. Do not over-tighten as this can damage the fitting or crush the O-ring.
7. 7

   Reconnect electrical connector
   Push the electrical connector firmly onto the new switch terminal until it clicks or seats completely. Ensure the connection is secure by gently tugging on the connector body.
8. 8

   Reconnect battery
   Reconnect the negative battery cable to the battery terminal and tighten securely.
9. 9

   Evacuate AC system
   Connect the vacuum pump and manifold gauge set to the AC system service ports. Pull a vacuum on the system for a minimum of 30 minutes. Monitor the gauges to ensure the system holds vacuum without rising, which would indicate a leak. If vacuum holds steady for 10 minutes after pump shutoff, the system is sealed.
10. 10

    Recharge AC system
    Using the appropriate refrigerant for your system (R-12 or R-134a), recharge the AC system to the factory specified amount. For original R-12 systems, charge to the factory-specified capacity per the 1966 Corvette service manual (verify exact amount before charging). For converted R-134a systems, use approximately 85% of the original R-12 capacity. Monitor system pressures during charging to ensure proper fill.

Reassembly

1. Ensure all electrical connections are secure and properly seated
2. Verify no refrigerant leaks are present at the switch connection
3. Double-check that the negative battery cable is securely tightened

Verification

• Start the engine and turn on the AC system to maximum cooling
• Allow system to run for 5 minutes and verify cold air is produced
• Check that the AC compressor cycles on and off normally, indicating the low pressure switch is functioning
• Use a leak detector or soap solution to verify no leaks at the switch connection point
• Monitor system pressures with gauges to confirm proper operation: low side should be 25-35 psi at idle with system stabilized
• Verify the AC clutch disengages if low pressure drops too low, confirming switch protection function

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