AC Expansion Valve (TXV)

This procedure removes and replaces the AC expansion valve (TXV) on a 1966 Chevrolet Corvette with 327ci V8, including refrigerant recovery, line disconnection, and system recharge.

Warnings

Tools required

Parts

• AC expansion valve (TXV) × 1 — Use OEM specification or equivalent for 1966 Corvette factory AC
• AC line O-rings or flare gaskets × 1 — Use OEM specification
• R12 refrigerant or R134a retrofit kit × 1 — Approximately 3 lbs R12 or equivalent

Preparation

1. Park vehicle on level surface and engage parking brake
2. Allow engine and AC system to reach ambient temperature (minimum 2 hours cool-down if recently operated)
3. Disconnect negative battery cable to prevent accidental blower motor operation
4. Verify EPA certification and proper refrigerant recovery equipment is available
5. Locate the expansion valve - typically mounted at the firewall on the evaporator inlet line, accessible from engine bay on passenger side
6. Place drip pan beneath work area to catch any residual oil

Procedure

1. 1

   Recover refrigerant from AC system
   Connect R12 recovery machine to the AC service ports (low and high side). Follow recovery machine manufacturer's instructions to completely evacuate all refrigerant from the system. Continue recovery until gauges read vacuum and machine confirms recovery is complete. Document the amount of refrigerant and oil removed for recharge reference. Allow system to stabilize for 5 minutes after recovery to ensure no residual pressure remains.
2. 2

   Access expansion valve at firewall
   From the engine bay, locate the expansion valve on the passenger side firewall where the evaporator inlet line enters. The valve is mounted inline on the liquid line just before the evaporator. You may need to remove the passenger side inner fender splash shield or air cleaner assembly for better access. Clean the area around the valve and connecting lines with shop rags to prevent contamination.
3. 3

   Disconnect sensing bulb
   The expansion valve has a capillary tube with sensing bulb clamped to the evaporator outlet (suction) line. Carefully unclamp or unbolt the sensing bulb from the suction line. Note the exact position and orientation of the bulb for reinstallation - it must contact the line at the same location for proper operation. Do not kink or damage the capillary tube.
4. 4

   Disconnect inlet line from expansion valve
   Using the appropriate flare nut wrench, carefully loosen and disconnect the liquid line (inlet) from the expansion valve inlet port. This is the line coming from the condenser/receiver-drier. Back up the valve body with a second wrench to prevent twisting the evaporator connection. Cap or plug the open line immediately to prevent moisture and contamination from entering the system.
5. 5

   Disconnect outlet line from expansion valve
   Disconnect the outlet side of the expansion valve from the evaporator inlet. Depending on configuration, this may be a flare fitting or the valve may be directly brazed or clamped into the evaporator line. If flare fitting, use flare nut wrench and back-up wrench. If brazed, you will need to cut the line and install new fittings during reassembly. Cap or plug the evaporator line opening immediately.
6. 6

   Remove expansion valve
   With both lines disconnected, remove any mounting brackets or clamps securing the expansion valve to the firewall or evaporator case. Remove the old expansion valve assembly with capillary tube and sensing bulb intact. Inspect the old valve for contamination, ice formation evidence, or debris. Drain any residual oil from the valve into the drip pan and measure quantity for replacement reference.
7. 7

   Inspect lines and fittings
   Inspect both refrigerant line ends for damage, corrosion, or deformed flare seats. Replace any damaged flare fittings or O-rings. Check the evaporator inlet tube for blockage or restriction. If converting from R12 to R134a, this is the time to install retrofit fittings if needed.
8. 8

   Prepare new expansion valve
   Remove the new expansion valve from packaging only when ready to install to minimize moisture exposure. Verify the valve is the correct type and capacity for the 1966 Corvette system. Add the appropriate amount of refrigerant oil to the new valve inlet - typically 1-2 ounces of mineral oil for R12 systems or the appropriate oil for R134a conversion. Verify the sensing bulb capillary tube is undamaged.
9. 9

   Install new expansion valve
   Position the new expansion valve in the mounting location at the firewall. Orient the valve so the sensing bulb capillary tube will reach the evaporator outlet (suction) line without strain or sharp bends. Secure any mounting brackets or clamps. Do not fully tighten line connections yet.
10. 10

    Connect inlet line to expansion valve
    Remove the cap from the liquid line. Install a new flare gasket or O-ring if applicable. Thread the inlet line fitting onto the expansion valve inlet port by hand to ensure proper thread engagement. Using flare nut wrench and back-up wrench, tighten the connection snugly. Do not overtighten the flare fittings - for the factory steel flare fittings, tighten to the manufacturer's specified torque (verify spec); hand tight plus a small additional turn is typical for flare fittings.
11. 11

    Connect outlet line to expansion valve
    Remove the cap from the evaporator inlet line. Install new flare gasket or O-ring as needed. Connect the expansion valve outlet to the evaporator inlet fitting. If you had to cut a brazed connection, install the appropriate union or adapter fittings now. Tighten connection snugly using proper technique to avoid overtightening.
12. 12

    Install sensing bulb
    Position the expansion valve sensing bulb on the evaporator outlet (suction) line at the location noted during disassembly - typically on a horizontal section of the larger suction line, positioned at the 4 o'clock or 8 o'clock position (not top or bottom). Secure the bulb with the proper clamp, ensuring good thermal contact with the line. The bulb must sense the temperature of the refrigerant leaving the evaporator for proper valve operation.
13. 13

    Evacuate AC system
    Connect the vacuum pump and manifold gauges to the AC system service ports. Open both manifold valves and start the vacuum pump. Evacuate the system to at least 29 inches Hg vacuum. Continue vacuum for a minimum of 45 minutes to remove all moisture and air. After 45 minutes, close the manifold valves, shut off the pump, and observe the vacuum gauge for 15 minutes - the vacuum should hold steady indicating no leaks.
14. 14

    Recharge AC system
    With system still under vacuum, connect the refrigerant supply (R12 or R134a as appropriate). Charge the system with the amount of refrigerant recovered plus replacement for what was in the old expansion valve (follow the factory R12 charge specification from the 1966 Corvette service manual (verify exact quantity before charging), or follow R134a conversion specifications which is typically 80-85% of R12 capacity). With the compressor OFF, charge liquid refrigerant into the high side only until flow stops. Never charge liquid into the low side. Then close the high side, start the engine, set AC to maximum and blower on high, and add the remaining charge slowly as vapor through the low side. Monitor pressures on manifold gauges throughout charging. Monitor pressures on manifold gauges throughout charging.
15. 15

    Leak test all connections
    With system fully charged and stabilized, use electronic leak detector or UV dye/light to check all connections at the expansion valve, inlet line, outlet line, and sensing bulb area. Check for proper system pressures - with R12 at 75-80°F ambient, expect approximately 25-30 psi low side and 175-225 psi high side at idle. Verify compressor cycling and evaporator cooling are normal.

Reassembly

1. Reinstall any components removed for access (inner fender shields, air cleaner, etc.)
2. Reconnect negative battery cable
3. Verify all tools and materials are removed from engine bay
4. Document refrigerant type and quantity charged on underhood label if converting from R12 to R134a

Verification

• Start engine and set AC to maximum cold, high blower speed
• Verify compressor clutch engages and cycles properly
• Check that center dash vents deliver cold air (40-50°F at vents in 75-80°F ambient)
• Feel evaporator inlet and outlet lines - inlet should be warm, outlet should be cold with possible light frost
• Monitor AC pressures with manifold gauges - pressures should be within normal range for ambient temperature
• Verify no refrigerant leaks at expansion valve connections using leak detector
• Check that sensing bulb remains securely clamped to suction line
• Test system operation for 15-20 minutes to confirm proper cooling and no abnormal cycling

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