AC Expansion Valve (TXV)

Replace the thermal expansion valve (TXV) in the factory air conditioning system, requiring refrigerant recovery, evaporator case access, and system recharge.

Warnings

Tools required

Parts

• AC expansion valve (TXV) × 1 — Use OEM specification
• TXV O-rings or gasket kit × 1 — Use OEM specification
• Refrigerant oil (mineral oil for R-12) × 1 — Use OEM specification
• Receiver-drier × 1 — Use OEM specification

Fluids

• R-12 refrigerant

Preparation

1. Park vehicle on level surface and engage parking brake
2. Disconnect negative battery cable
3. Allow engine to cool completely if recently run
4. Verify AC system contains refrigerant (check sight glass or manifold gauges)
5. Position drip pans under work area to catch residual oil

Procedure

1. 1

   Recover refrigerant from system
   Connect R-12 recovery machine to high and low side service ports. Follow recovery machine instructions to evacuate all refrigerant from the system into approved recovery tank. Monitor gauges until both high and low side read 0 psi or vacuum. Allow system to stabilize for several minutes and re-check gauges; refrigerant dissolved in the oil can cause pressure to rebuild, requiring an additional recovery cycle until pressure remains at 0 psi/vacuum.
2. 2

   Access evaporator case
   From inside the cab, locate the evaporator case assembly mounted under the dash on the passenger side. Remove the glove box door and glove box assembly by removing the glove box mounting screws (verify exact count against factory service manual for the 1972 F-100). Remove the lower dash trim panel below the glove box area to improve access to the evaporator case cover.
3. 3

   Disconnect refrigerant lines at firewall
   Working from the engine compartment, locate the liquid line and suction line connections at the firewall near the evaporator case. Use line wrenches to disconnect both refrigerant lines at the firewall fittings. Immediately cap or plug all open refrigerant ports to prevent moisture entry. Expect small amounts of refrigerant oil to drain from the lines.
4. 4

   Remove evaporator case cover
   From inside the cab, remove the screws securing the evaporator case cover. The cover is held by several sheet metal screws around the perimeter (verify exact count against factory service manual for the 1972 F-100 with factory AC). Carefully separate the cover from the case housing, noting the location of any sealing foam. Set the cover aside with screws organized.
5. 5

   Locate and document TXV orientation
   With the case open, locate the thermal expansion valve mounted at the evaporator inlet. The TXV has a liquid line connection, an evaporator outlet connection, and a thermal sensing bulb clamped to the suction line. Take note or photograph the exact routing and position of the sensing bulb and its capillary tube before removal.
6. 6

   Remove sensing bulb
   Carefully remove the clamp securing the TXV sensing bulb to the evaporator outlet (suction) line. The bulb must be mounted in good thermal contact with the suction line. Note the exact position (typically on bottom or side of the tube, never on top).
7. 7

   Disconnect TXV from evaporator
   Remove the mounting hardware securing the TXV body to the evaporator case. Disconnect the inlet line fitting at the TXV (liquid line from condenser). Disconnect the outlet fitting where the TXV connects to the evaporator coil inlet. Remove the old TXV assembly complete with sensing bulb and capillary tube.
8. 8

   Inspect and clean mating surfaces
   Inspect the evaporator inlet tube and line connection surfaces for corrosion, damage, or old gasket material. Clean all mating surfaces with a clean shop towel. Check that the internal screen filter (if equipped at evaporator inlet) is clean and not clogged. Inspect evaporator coil fins for obvious damage or blockage.
9. 9

   Prepare new TXV
   Unpack the new thermal expansion valve. Lubricate all new O-rings or gaskets with clean refrigerant oil (mineral oil for R-12 systems). Install new O-rings onto the TXV inlet and outlet connections. Add 1-2 ounces of fresh refrigerant oil to the TXV inlet to replace oil lost during service.
10. 10

    Install new TXV
    Position the new TXV onto the evaporator inlet connection, ensuring proper alignment and seating of O-rings. Install the mounting hardware to secure the TXV body. Connect the liquid line to the TXV inlet fitting and tighten securely with line wrench. Connect the TXV outlet to the evaporator coil inlet.
11. 11

    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 mounted at the 4 o'clock or 8 o'clock position on the tube for proper oil return sensing, never at the top (12 o'clock). Secure with the provided clamp, ensuring firm contact without crushing the tube. Route the capillary tube to avoid kinks or contact with sharp edges.
12. 12

    Reinstall evaporator case cover
    Position any foam sealing strips back into their original locations on the case. Install the evaporator case cover and secure with all of the sheet metal screws removed during disassembly. Ensure a proper seal to prevent air bypass around the evaporator core.
13. 13

    Reconnect refrigerant lines at firewall
    Remove caps or plugs from refrigerant line fittings. Connect both the liquid line and suction line at the firewall connections, tightening securely with line wrenches. Do not overtighten aluminum fittings.
14. 14

    Replace receiver-drier
    Locate the receiver-drier in the engine compartment (typically mounted near the condenser or on the firewall). Disconnect the inlet and outlet lines using line wrenches. Remove the mounting bracket hardware and remove the old receiver-drier. Install the new receiver-drier, keeping it capped until immediately before connection. Connect inlet and outlet lines and secure mounting bracket.
15. 15

    Evacuate system
    Connect vacuum pump to both high and low side service ports via manifold gauge set. Open both manifold valves and pull a deep vacuum on the system for a minimum of 45 minutes. System should reach 29 inches of mercury vacuum. After evacuation, close manifold valves and shut off vacuum pump. Monitor gauges for 10 minutes to verify system holds vacuum (no leak present).
16. 16

    Recharge system with R-12
    With vacuum verified, connect R-12 refrigerant supply to manifold gauge set. Charge the system with the manufacturer-specified amount of R-12 refrigerant (typically 2.0-2.5 lbs for this system, verify exact capacity on underhood AC specification label). Charge liquid refrigerant into the low side with engine off, then run engine and AC system on MAX/RECIRCULATE and add remaining refrigerant through low side as vapor until proper charge is achieved per sight glass (clear with occasional bubbles). Verified detail (The R-12 charge capacity is an unverified AI guess per openQuestions. 2.75-3.25 lbs is high for a light-truck factory system and should be confirmed against the underhood decal or factory spec.): Charge the system with the manufacturer-specified amount of R-12 refrigerant (verify exact capacity against the underhood AC charge decal or factory service manual for the 1972 F-100). Verified detail (This is in step 15 (Evacuate system), not step 16. However, 10 minutes is a relatively short vacuum hold test for verifying system integrity after opening an AC system. Industry standard is typically 30 minutes to 1 hour for proper leak verification.): Monitor gauges for 30 minutes to verify system holds vacuum (no leak present). System should not rise more than 1-2 inches of vacuum during this period.

Reassembly

1. Reinstall lower dash trim panel and glove box assembly inside cab
2. Reconnect negative battery cable
3. Check all refrigerant line connections for tightness
4. Wipe down all components and clean work area

Verification

• Start engine and turn AC system to MAX with blower on high
• Allow system to run for 5 minutes and verify cold air from vents (typically 40-50°F at vent with 90°F ambient)
• Check sight glass (if equipped) for clear refrigerant flow with only occasional bubbles indicating proper charge
• Verify both refrigerant lines show appropriate temperature (liquid line warm, suction line cold and sweating)
• Use leak detector to check all connections for refrigerant leaks
• Monitor gauge pressures: low side should be 25-35 psi, high side 175-250 psi depending on ambient temperature
• Verify clutch cycling is appropriate (should not short-cycle or run continuously)
• Test system operation in various modes and blower speeds

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