AC Evaporator

Complete removal and replacement of the air conditioning evaporator core, including discharging the AC system, removing the evaporator case from inside the cab, and recharging the system.

Warnings

Tools required

Parts

• AC evaporator core × 1 — Use OEM specification or equivalent for 1972 F-100
• Evaporator case foam seal kit × 1 — Use OEM specification
• Expansion valve × 1 — Replace if corroded or contaminated
• Receiver-drier × 1 — Must be replaced whenever system is opened
• AC system O-ring kit × 1 — Use R-12 compatible O-rings
• PAG oil for R-12 system × 1 — Use correct viscosity for 1972 system
• R-12 refrigerant × 1 — See fluid specs for capacity

Fluids

• R-12 refrigerant

Preparation

1. Park vehicle on level surface and apply parking brake
2. Disconnect negative battery cable
3. Allow engine to cool completely if recently operated
4. Verify AC recovery machine is functioning and has adequate tank capacity
5. Place protective covering over bench seat and floor to prevent interior damage
6. Ensure replacement parts are available before beginning work, as system must not remain open to atmosphere for extended periods

Procedure

1. 1

   Recover R-12 refrigerant from system
   Connect R-12 recovery machine to service ports on AC system. Follow recovery machine manufacturer's instructions to completely evacuate all refrigerant from the system. Ensure recovery is complete before disconnecting hoses. Record amount of refrigerant recovered for recharge reference.
2. 2

   Disconnect AC lines at firewall
   Working from engine compartment, locate the liquid line and suction line connections at the firewall where they enter the evaporator case. Use appropriate line disconnect tools or wrenches to disconnect both lines from the evaporator. Immediately cap all open fittings with plugs or tape to prevent moisture and debris entry. Inspect O-rings and discard (new ones will be installed).
3. 3

   Drain coolant and disconnect heater hoses
   Place drain pan under radiator and drain approximately 2 quarts of coolant from the system (enough to drop level below heater core). Locate the two heater hoses at the firewall and use pliers to release the hose clamps. Disconnect both heater hoses from the heater core tubes. Cap or plug the heater core tubes to minimize coolant spillage into the cab.
4. 4

   Remove glove box
   Open glove box door fully. Remove the 4 screws securing the glove box to the dash assembly (2 at top, 2 at bottom). Disconnect glove box light wire if equipped. Remove glove box from vehicle to provide access to evaporator case.
5. 5

   Disconnect blower motor wiring
   Locate the blower motor on the passenger side of the evaporator case. Disconnect the electrical connector from the blower motor. If equipped with a blower resistor block, disconnect its wiring harness as well. Verified detail (A 1972 Ford F-100 is entirely SAE/standard fasteners; metric tools are unnecessary and their inclusion suggests generic content not tailored to the platform.): Wrench set (standard/SAE)
6. 6

   Remove blower motor assembly
   Remove the 3 screws securing the blower motor housing to the evaporator case. Carefully extract the blower motor and squirrel cage fan assembly from the case. Set aside for reinstallation.
7. 7

   Disconnect evaporator case control cables and vacuum lines
   Locate the temperature blend door cable and mode control cables attached to the evaporator case. Disconnect each cable by releasing the retaining clip and sliding the cable end off its mounting arm. Disconnect any vacuum lines attached to vacuum actuators on the case (typically 2-3 lines). Label or photograph connections for proper reassembly.
8. 8

   Remove evaporator case mounting hardware
   Remove the 5 nuts securing the evaporator case to the firewall studs (accessible from inside the cab on the passenger side). Remove the 2 screws securing the lower portion of the case to the floor pan support bracket. Support the case with one hand as you remove the final fasteners.
9. 9

   Extract evaporator case from vehicle
   Carefully maneuver the evaporator case assembly away from the firewall, guiding the AC and heater core tubes through their firewall grommets. Tilt and rotate the case as necessary to clear the dash structure and steering column. Remove the complete case assembly from the vehicle and place on a clean work surface.
10. 10

    Disassemble evaporator case
    With the case on the workbench, remove the 8 metal spring clips or screws securing the upper and lower case halves together. Carefully separate the two halves. Remove the evaporator core from the lower case half. Remove the expansion valve from the evaporator core inlet tube (typically held by 2 screws and a clamp). Inspect the expansion valve screen for debris or contamination.
11. 11

    Clean case and install new evaporator
    Thoroughly clean both case halves, removing any old foam seals, debris, or corrosion. Inspect drain tube for blockage and clear if necessary. Install new foam seals from the seal kit onto the evaporator mounting surfaces in the lower case half. Install the new expansion valve onto the new evaporator core inlet tube with new O-rings, ensuring the sensing bulb is properly positioned. Place the new evaporator core into the lower case half, ensuring proper alignment with mounting tabs and tube passages.
12. 12

    Reassemble and seal evaporator case
    Apply new foam seal tape to the mating flange of the lower case half where specified. Carefully position the upper case half onto the lower half, ensuring all internal doors, linkages, and the evaporator core are properly aligned. Install all 8 spring clips or screws to secure the case halves together. Verify the case is properly sealed with no gaps.
13. 13

    Install evaporator case into vehicle
    Maneuver the reassembled evaporator case back into position in the vehicle, guiding the heater core and evaporator tubes through the firewall grommets. Align the case mounting studs with the firewall holes. Install the 5 nuts onto the firewall studs finger-tight. Install the 2 lower floor pan mounting screws. Tighten all mounting hardware securely.
14. 14

    Reconnect control cables and vacuum lines
    Reconnect all temperature and mode control cables to their respective arms on the evaporator case, ensuring proper cable routing and securing retaining clips. Reconnect all vacuum lines to their original positions based on labels or photographs from disassembly. Test operation of all control doors by moving the dash controls through their full range.
15. 15

    Reinstall blower motor and glove box
    Reinstall the blower motor assembly into its opening in the evaporator case and secure with the 3 mounting screws. Reconnect the blower motor electrical connector and resistor block wiring. Reinstall the glove box assembly and secure with the 4 mounting screws. Reconnect glove box light if equipped.
16. 16

    Reconnect heater hoses and refill coolant
    Working from the engine compartment, reconnect both heater hoses to the heater core tubes at the firewall. Secure with hose clamps, positioning clamps beyond the bead on the tubes. Refill cooling system with ethylene glycol coolant mixed 50/50 with water to proper level. Start engine and verify no coolant leaks at heater hose connections.
17. 17

    Install new receiver-drier
    Locate the receiver-drier (typically mounted near the condenser in the engine compartment). Remove the old receiver-drier by disconnecting the inlet and outlet lines. Install the new receiver-drier with new O-rings on all connections. Do not remove the protective caps on the new drier until immediately before installation to minimize moisture exposure.
18. 18

    Reconnect AC lines at firewall with new O-rings
    Install new O-rings on all AC line connections at the firewall. Apply a small amount of clean mineral refrigerant oil (R-12 compatible) to the O-rings. Reconnect the liquid line and suction line to the evaporator case fittings. Tighten connections to proper torque specification using a flare nut wrench or line wrench to avoid damaging fittings.
19. 19

    Evacuate AC system
    Connect vacuum pump to AC service ports using manifold gauge set. Evacuate the system to 29+ inches of mercury vacuum. Maintain vacuum for minimum 45 minutes (60 minutes preferred) to remove all moisture from the system. After evacuation period, close manifold valves and observe vacuum gauge for 15 minutes to verify system holds vacuum (indicating no leaks).
20. 20

    Recharge AC system with R-12
    With system under vacuum and all connections verified, recharge the system with R-12 refrigerant to the proper capacity. Use charging scale or charging cylinder to measure exact amount. Add mineral refrigerant oil as needed based on amount lost during recovery and in old components (typically 3-4 oz for evaporator replacement). Follow proper R-12 charging procedure: charge liquid into low side with engine off until pressure equalizes, then start engine and complete charge with vapor into low side while running. Verified detail (Should specify mineral oil for an R-12 system to avoid confusion with PAG oil referenced in the parts list.): Add mineral refrigerant oil (R-12 compatible) as needed based on amount lost during recovery and in old components.
21. 21

    Leak test and verify system operation
    With system fully charged, use electronic leak detector or soap solution to check all connections for leaks, paying special attention to firewall connections and receiver-drier fittings. Start engine and turn AC to maximum cooling. Verify blower motor operation at all speeds, proper airflow through all vents, and cold air temperature (center vent discharge should be 38-42°F with 95°F ambient). Check compressor clutch engagement and cycling. Verify system pressures are within normal range using manifold gauges.

Reassembly

1. Reconnect negative battery cable after all work is complete and verified
2. Test all heater and AC functions including mode changes, temperature control, and blower speeds
3. Verify no coolant or refrigerant leaks after 24 hours of operation
4. Check and top off coolant level after first heat cycle

Verification

• AC system holds proper charge with no loss of refrigerant pressure after 24 hours
• Center vent discharge air temperature is 38-42°F with maximum AC and recirculate mode
• Blower motor operates smoothly at all speed settings
• No refrigerant odor inside cab (sweet/chemical smell would indicate leak)
• Heater produces hot air when heater mode is selected, confirming heater core circulation is not blocked
• No coolant leaks at heater hose connections under pressure
• All mode doors operate correctly (defrost, floor, vent positions)
• Compressor cycles on and off appropriately as system reaches temperature

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