AC Orifice Tube

Replace the AC orifice tube in the liquid line between the condenser and evaporator to restore proper refrigerant flow and cooling performance.

Warnings

Tools required

Parts

• AC orifice tube × 1 — Use OEM specification or standard R-12 orifice tube
• Liquid line O-rings × 2 — Use OEM specification
• PAG or mineral oil for R-12 systems × 1 — Use mineral oil compatible with R-12

Fluids

• R-12 refrigerant — 0.875 qt

Preparation

1. Park vehicle on level surface and engage parking brake
2. Allow engine to cool completely if recently operated
3. Verify AC system uses orifice tube design (not expansion valve) by locating liquid line between condenser and evaporator
4. Connect R-12 recovery machine to high and low side service ports
5. Recover all refrigerant from system per EPA regulations and record amount recovered
6. Verify system is fully evacuated by checking manifold gauges read 0 PSI on both sides

Procedure

1. 1

   Locate orifice tube in liquid line
   The orifice tube is located in the liquid line between the condenser (front of vehicle) and the firewall. Look for a slight bulge or dimple in the liquid line approximately 6 to 12 inches from the condenser outlet. This bulge indicates the orifice tube location inside the line. On aftermarket orifice tube conversions, this is typically on the passenger side near the firewall. Factory systems use an expansion valve instead.
2. 2

   Disconnect liquid line at orifice tube location
   Using appropriate size line wrench, carefully loosen the flare nut fittings on both sides of the orifice tube location. The liquid line may have a union fitting at this point, or you may need to disconnect at the nearest fitting upstream. Support the line to prevent bending or kinking. A small amount of residual refrigerant or oil may escape.
3. 3

   Extract the orifice tube
   Insert the orifice tube puller tool into the liquid line opening. The tool has small hooks that grab the orifice tube screen. Twist and pull firmly to extract the orifice tube from the line. If the tube is stuck due to corrosion or debris, work the puller tool back and forth while pulling. Avoid excessive force that could damage the line. Verified detail (Factory 1972 F-100 systems use expansion valves, not orifice tubes. The procedure should verify the system has been converted to orifice tube design rather than assuming factory configuration uses this design.): Verify AC system has been converted to orifice tube design (factory systems use expansion valve). Orifice tubes are located in the liquid line between condenser and evaporator and create a visible bulge or dimple in the line.
4. 4

   Inspect orifice tube and system condition
   Examine the removed orifice tube carefully. Check the screen for metal shavings, black debris, or excessive sludge which indicates compressor failure or system contamination. If metal debris is present, the compressor has failed and the entire system requires flushing before installing new orifice tube. Check the brass tube portion for integrity. Minor discoloration is normal.
5. 5

   Clean liquid line opening
   Using shop rags and compressed air if available, clean the inside of the liquid line where the orifice tube sits. Remove any debris, old O-ring material, or contamination. The bore must be clean and smooth for proper orifice tube seating. Do not allow dirt or foreign material to enter the line.
6. 6

   Prepare new orifice tube
   Remove new orifice tube from packaging. Apply a thin coat of clean mineral refrigerant oil (mineral oil is the correct lubricant for R-12 systems) to the O-rings on the orifice tube body. Verify the color coding or size marking matches the original tube. Most Ford R-12 systems use a specific orifice size indicated by color.
7. 7

   Install new orifice tube
   Insert the new orifice tube into the liquid line opening with the shorter end (inlet side) facing toward the condenser. The tube has a specific directional flow indicated by an arrow or the screen location. Push firmly until the orifice tube seats fully and the O-rings seal against the line bore. The tube should be flush or slightly recessed from the line end.
8. 8

   Reconnect liquid line fittings
   Install new O-rings on all disconnected fittings, lubricating with clean refrigerant oil. Reconnect the liquid line fittings hand-tight first to ensure proper thread engagement. Using line wrenches, tighten the flare nut fittings snugly. Do not overtighten as this can damage the soft aluminum or brass fittings. Fittings should be tight enough to seal but not forced.
9. 9

   Evacuate the AC system
   Connect AC vacuum pump to both high and low side service ports through manifold gauges. Open both gauge valves and operate vacuum pump for minimum 45 minutes to remove all air and moisture from the system. System should pull down to 29 inches of vacuum and hold steady for 15 minutes after pump is shut off. Any vacuum loss indicates a leak that must be repaired.
10. 10

    Recharge system with R-12 refrigerant
    With system still under vacuum, close manifold gauge valves. Connect R-12 refrigerant supply to low side port. Start engine and set AC controls to maximum cold and high blower. Open low side valve slowly and allow system to draw in refrigerant. Add R-12 refrigerant as specified for your system (typically 3.0 pounds for 1972 F-100 factory AC, but verify with system specifications or amount recovered). Monitor pressures during charging. Low side should be 25 to 35 PSI and high side 175 to 225 PSI at idle with ambient temperature 75 to 85°F.

Reassembly

1. Verify all line fittings are properly tightened and secure
2. Check for refrigerant leaks at all fittings using electronic leak detector or soap solution
3. Confirm proper compressor clutch engagement when AC is activated

Verification

• Start engine and allow to idle for 5 minutes with AC on maximum cold
• Verify AC low side pressure reads 25 to 35 PSI and high side reads 175 to 225 PSI at idle
• Check that center dash vents blow cold air at 40 to 50°F with ambient temperature 75 to 85°F
• Listen for normal compressor operation without unusual noises or excessive cycling
• Inspect all fittings for oil seepage or frost formation indicating leaks
• Test AC performance during brief road test under load

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