AC Expansion Valve (TXV)

Replace the AC expansion valve (TXV) on a 1992 Dodge Viper 8.0L V10, requiring refrigerant recovery, removal of AC lines, and installation of new valve with proper sealing.

Warnings

Tools required

Parts

• AC expansion valve (TXV) × 1 — Use OEM specification
• AC line O-rings × 4 — Use OEM specification, appropriate for R-12
• PAG oil × 1 — Compatible with R-12 retrofit or original system

Preparation

1. Ensure engine is cold before beginning work
2. Park vehicle on level surface and engage parking brake
3. Verify AC system has not been recently operated (allow 15 minutes minimum for pressure equalization)
4. Gather all replacement parts and verify O-ring compatibility with R-12 refrigerant
5. Have refrigerant recovery equipment ready and certified personnel available

Procedure

1. 1

   Recover refrigerant from AC system
   Connect AC recovery machine to system service ports (low side on suction line, high side on liquid line near condenser/receiver-drier). Follow machine manufacturer procedures to fully recover all R-12 refrigerant from the system. Verify system is at 0 PSI on both high and low sides before proceeding. Document refrigerant amount recovered for recharge reference.
   ⚠️This step must be performed by EPA-certified technician. Venting R-12 to atmosphere is illegal and hazardous.
2. 2

   Access expansion valve area
   Open hood and locate the expansion valve on the passenger side firewall area where the AC lines enter the evaporator housing. The valve is typically positioned at the evaporator inlet with liquid line entering and evaporator outlet exiting. Remove any engine covers or components obstructing clear access to the valve and connecting lines. On the Viper, this may require moving aside harness bundles or coolant overflow reservoir for better access.
   ℹ️Take photos of line routing and valve orientation before removal for installation reference.
3. 3

   Disconnect liquid line from expansion valve inlet
   Place shop towels around the liquid line connection at the expansion valve inlet. Using appropriate line wrench, loosen and remove the liquid line fitting from the valve inlet. Cap or plug the open line immediately to prevent moisture and debris entry. Remove and discard the old O-ring from the line fitting.
   ⚠Residual oil may drain from connections. Have towels ready to catch spillage.
   Torque spec

   AC Line Fittings27 Nm (20 lb-ft)
4. 4

   Disconnect evaporator line from expansion valve outlet
   Place shop towels around the evaporator inlet line connection at the expansion valve outlet. Using line wrench, loosen and remove the evaporator line fitting from the valve outlet. Cap or plug the open line immediately. Remove and discard the old O-ring from the line fitting.
   Torque spec

   AC Line Fittings27 Nm (20 lb-ft)
5. 5

   Remove expansion valve from evaporator
   The expansion valve body is secured to the evaporator housing with 2 mounting bolts. Remove these bolts and carefully extract the expansion valve assembly from the evaporator housing. Remove and discard the O-rings from the valve body where it seals to the evaporator. Inspect the evaporator port for debris or damage.
   ℹ️Note the orientation of the valve sensing bulb and capillary tube routing for proper installation of replacement valve.
   Torque spec

   Expansion Valve23 Nm (17 lb-ft)
6. 6

   Inspect and clean mounting surfaces
   Thoroughly clean the evaporator housing mounting surface where the expansion valve seals, removing any old O-ring material, debris, or corrosion. Inspect the surface for damage, deep scratches, or pitting that could prevent proper sealing. Clean the AC line fitting threads and sealing surfaces. Verify the new expansion valve matches the original in configuration and sensing bulb type.
   ⚠Do not allow any debris to enter the open evaporator ports. Keep area clean and consider covering ports with tape during cleaning.
7. 7

   Install new O-rings and prepare expansion valve
   Lubricate new O-rings with thin coat of compatible refrigerant oil (mineral oil for R-12 system, PAG oil only if retrofitted to R-134a). Install new O-rings onto the expansion valve body where it seals to the evaporator housing. Lubricate the O-rings after installation. Install new O-rings onto both AC line fittings (liquid line and evaporator line) and lubricate with the same compatible oil. Add approximately 1-2 ounces of the appropriate refrigerant oil into the expansion valve inlet to replace oil lost during service. service. Note: Use mineral oil for the original R-12 system, or PAG oil only if the system has been retrofitted to R-134a. Do not over-lubricate O-rings.
   ℹ️Use only PAG oil compatible with R-12 system or intended retrofit refrigerant. Do not over-lubricate O-rings.
8. 8

   Install expansion valve to evaporator
   Carefully position the new expansion valve into the evaporator housing, ensuring proper orientation matches original installation with sensing bulb positioned correctly. Start both mounting bolts by hand to verify proper alignment. Tighten the mounting bolts to specification in a crossing pattern to ensure even seating.
   ⚠Do not cross-thread the mounting bolts. Ensure valve seats fully and squarely against evaporator housing before tightening.
   Torque spec

   Expansion Valve23 Nm (17 lb-ft)
9. 9

   Connect evaporator line to expansion valve outlet
   Remove the cap or plug from the evaporator line. Verify the new lubricated O-ring is properly seated in the fitting. Hand-thread the evaporator line fitting onto the expansion valve outlet, ensuring it threads smoothly without cross-threading. Using line wrench, tighten the fitting to specification.
   ⚠Use line wrench to prevent rounding of fitting. Do not over-tighten as this can damage O-ring seal.
   Torque spec

   AC Line Fittings27 Nm (20 lb-ft)
10. 10

    Connect liquid line to expansion valve inlet
    Remove the cap or plug from the liquid line. Verify the new lubricated O-ring is properly seated in the fitting. Hand-thread the liquid line fitting onto the expansion valve inlet, ensuring smooth threading. Using line wrench, tighten the fitting to specification.
    Torque spec

    AC Line Fittings27 Nm (20 lb-ft)
11. 11

    Secure expansion valve sensing bulb
    Route the expansion valve sensing bulb capillary tube to match original configuration. Secure the sensing bulb to the evaporator outlet line (suction line) in the correct orientation, typically at the 12 o'clock or 3 o'clock position on the line. The bulb must have good thermal contact with the line. Use the original securing method (clamp or tape as equipped from factory).
    ℹ️Proper sensing bulb placement is critical for expansion valve operation. Bulb must sense actual evaporator outlet temperature.
12. 12

    Reinstall any displaced components
    Reinstall any engine covers, harness bundles, coolant overflow reservoir, or other components that were moved for access. Ensure all components are properly secured and no harnesses are pinched or stressed. Verify AC line routing matches original configuration with no kinks or excessive bends.
13. 13

    Evacuate AC system
    Connect vacuum pump to AC system service ports. Evacuate the system to full vacuum (minimum 29 inches Hg) and hold for minimum 30 minutes. Monitor vacuum gauge for any pressure rise that would indicate a leak. If system holds vacuum, proceed to recharge. If vacuum does not hold, locate and repair leak before charging.
    ⚠Proper evacuation removes moisture and air from system. Inadequate evacuation will cause poor AC performance and potential compressor damage.
14. 14

    Recharge AC system
    Using AC recovery/recharge machine, charge the system with the amount of R-12 refrigerant documented during recovery step, or per factory specification if significantly different. Start engine and turn AC to maximum cooling. Monitor system pressures on gauge set. Typical operating pressures should be 25-35 PSI low side and 175-225 PSI high side at 2000 RPM with ambient temperature around 75-80°F.
    ℹ️Do not overcharge system. Follow equipment manufacturer procedures for accurate refrigerant charge by weight.

Reassembly

1. Reassembly is covered in the procedural steps above
2. Ensure all AC line connections are tight and leak-free
3. Verify expansion valve sensing bulb is properly secured to suction line with good thermal contact
4. Double-check that no tools or materials were left in engine bay

Verification

• Start engine and set AC to maximum cooling with blower on high
• Allow system to run for 5 minutes and verify cold air output from vents (typically 40-50°F at center vent)
• Check all AC line connections for signs of oil leakage indicating refrigerant leak
• Verify system pressures are within normal operating range using manifold gauges
• Monitor low side pressure to confirm it cycles appropriately as expansion valve modulates (pressure should vary slightly, not remain fixed)
• Listen for any unusual noises from expansion valve area or compressor
• Perform electronic leak check around all disturbed connections with AC leak detector
• Test AC performance in various operating conditions (idle, highway speed, varying ambient temperatures)

More procedures for this vehicle