AC Expansion Valve (TXV)

Replace the AC expansion valve (TXV) to restore proper refrigerant metering and AC cooling performance on the 1970 AMC Rebel Machine with factory air conditioning.

Warnings

Tools required

Parts

• AC expansion valve (TXV) × 1 — Use OEM specification for 1970 AMC factory AC
• TXV mounting gaskets or O-rings × 1 — Use OEM specification
• R134a refrigerant (if converted) or R12 substitute × 1 — Check system type

Preparation

1. Verify AC system type (original R12 or converted to R134a) by checking service port fittings and any conversion labels
2. Park vehicle on level surface and engage parking brake
3. Allow engine to cool completely if recently operated
4. Disconnect negative battery cable to prevent accidental fan engagement
5. Locate the expansion valve at the firewall near the evaporator inlet - typically on passenger side under hood

Procedure

1. 1

   Recover refrigerant from system
   Connect AC recovery machine to service ports. Follow machine instructions to completely recover all refrigerant from the system. Document the amount recovered for proper recharge quantity later. Verify system pressure reads zero on manifold gauges before proceeding.
2. 2

   Access expansion valve
   Remove any engine components blocking access to the expansion valve area. On the 390ci V8, this may include the air cleaner assembly and associated vacuum lines. The TXV is typically mounted at the evaporator inlet near the firewall on the passenger side. Mark or photograph line routing before disconnection.
3. 3

   Disconnect sensing bulb
   Carefully remove the TXV sensing bulb from the evaporator outlet (suction) line. The bulb is typically clamped to the line. Note the exact positioning and orientation of the bulb for reinstallation - proper sensing bulb placement is critical for correct TXV operation.
4. 4

   Disconnect refrigerant lines from TXV
   Using line wrenches to prevent rounding, carefully disconnect the inlet line from the liquid line (from condenser) and the outlet line to the evaporator. Have shop towels ready to catch any residual oil. Cap all open fittings immediately to prevent moisture and debris contamination.
5. 5

   Remove TXV from evaporator
   Remove the mounting hardware securing the TXV to the evaporator housing. The valve may be bolted or clamped depending on factory configuration. Carefully extract the valve and note the position of any gaskets or sealing washers.
6. 6

   Inspect evaporator connection and prepare surfaces
   Inspect the evaporator inlet connection for damage, corrosion, or debris. Clean the mating surfaces thoroughly. Check that no debris has entered the evaporator. Replace any damaged sealing surfaces or O-rings at the evaporator connection.
7. 7

   Install new TXV
   Install new gaskets or O-rings on the replacement TXV. Position the new valve onto the evaporator inlet, ensuring proper alignment. Install mounting hardware and tighten securely. The valve body should be oriented correctly for sensing bulb attachment to the evaporator outlet line.
8. 8

   Reconnect refrigerant lines
   Remove caps from refrigerant lines. Connect the liquid line (from condenser) to the TXV inlet and the evaporator outlet line to the TXV. Use line wrenches and tighten fittings snugly - avoid overtightening which can damage flare fittings. Hand-tighten first, then use wrench for final seating.
9. 9

   Install sensing bulb
   Position the TXV sensing bulb on the evaporator outlet (suction) line in the exact location noted during removal. The bulb should be on a horizontal or slightly inclined section of line, not at the bottom. Secure the bulb clamp tightly to ensure good thermal contact with the line.
10. 10

    Evacuate system
    Connect vacuum pump to system via manifold gauges. Evacuate system to at least 29 inches of mercury (Hg) vacuum. Maintain vacuum for minimum 30-45 minutes to remove all moisture and air. Longer evacuation time is better, especially in humid conditions. Close manifold valves and observe vacuum gauge - system should hold vacuum.
11. 11

    Recharge AC system
    With vacuum holding steady, charge system with the appropriate refrigerant type and quantity (typically 2.5-3.0 lbs for 1970 AMC factory AC, but verify specification). Charge through the low-side service port with engine running and AC on maximum. Use refrigerant scale for accurate measurement. Do not overcharge.
12. 12

    Check for leaks
    With system charged and pressurized, use electronic leak detector or soap solution to check all connection points at the TXV, refrigerant lines, and sensing bulb area. Pay special attention to newly disturbed fittings. Address any leaks before proceeding.

Reassembly

1. Reinstall any engine components removed for access (air cleaner assembly, vacuum lines)
2. Reconnect negative battery cable
3. Ensure all tools and materials are removed from engine compartment

Verification

• Start engine and turn AC to maximum cold and high blower speed
• Allow system to run for 10-15 minutes and verify cold air output from vents
• Check that compressor cycles properly and both high and low side pressures are within specification using manifold gauges
• Verify evaporator outlet line (suction line) is cold and sweating, indicating proper refrigerant flow through TXV
• Confirm no unusual noises from compressor or expansion valve area
• Recheck all connections for leaks after system has reached operating temperature
• Monitor system performance over next few days to ensure continued proper operation

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