5.5 Refrigerant Hoses, Lines, Fittings, Service Ports & Seals

The Task

ASE task B19 asks you to inspect, repair, or replace A/C system hoses, lines, filters, fittings, primary service ports (gauge connections), auxiliary service ports (safety switches), caps, O-rings, and seals. On a sleeper tractor these parts include long liquid and suction runs to the bunk unit, bulkhead fittings through the cab floor, flexible sections that absorb cab movement on air suspension, and clamps every couple of feet along the frame.

Hoses and Hard Lines

• Barrier hose: R-134a and R-1234yf use hoses with a nylon barrier liner. Their small molecules permeate plain rubber hose, and the liner also keeps moisture out and oil in.
• SAE J2064 covers refrigerant hose and hose assemblies for these systems. ASE's Section 609 training explains the markings. "J2064" or "J2064 R-134a" means approved for R-134a only. "J2064 R-134a/R-1234yf" or "J2064-R-1234yf" means approved for both. Use only correctly marked hose on an R-1234yf system.
• Crimped assemblies: truck shops often build hoses in-house with a crimper. Use the hose, ferrule, and fitting combination and the crimp die settings the crimper maker specifies for that hose type; an under-crimp leaks and an over-crimp cracks the ferrule. Check crimp diameter with the gauge supplied.
• Discharge hose mufflers: some discharge hoses include a muffler that damps compressor pulses. After a compressor failure the muffler can trap debris, so these hoses are usually replaced along with the other contaminated parts.
• Inspect for: oily residue at crimps (a leak), cracks, bulges, abrasion where hoses touch the frame, cab, or exhaust, heat damage near the exhaust, and kinks. A kinked or internally collapsed hose causes a restriction with a temperature drop at that point.
• Routing and clamping: restore every P-clamp, grommet, and standoff. Leave slack at the cab-to-frame transition so cab movement does not stretch lines. A line left rubbing on a frame rail will wear through.

Fittings and Seals

O-ring rules:

1. Never reuse an O-ring. Install one that matches the refrigerant (usually HNBR); color alone does not identify the material.
2. Inspect sealing surfaces for nicks, corrosion, and old O-ring material.
3. Lubricate new O-rings before installing them, as ASE's Section 609 training directs, using the oil the vehicle or system maker specifies.
4. Tighten fittings and flange bolts to the manufacturer's torque. Over-tightening crushes O-rings and cracks aluminum.
5. Leak-test after recharging.

Primary Service Ports and Caps

• The different sizes keep R-134a couplers off R-1234yf ports and the reverse. Any retrofit must use the new refrigerant's unique fittings and label, and any unconverted fittings must be permanently disabled.
• Caps are part of the seal. Each cap has its own seal that backs up the valve core. A missing cap lets dirt into the core and removes a sealing barrier. SAE J1628 leak checks test service valves with the caps on and with the caps removed.
• Valve cores are refrigerant-specific. Replace a leaking core with the correct core and tool. Special tools allow some cores to be changed without recovering the charge; otherwise recover first.
• Install gauge couplers with their shutoffs closed, and always recap the ports.

Auxiliary Service Ports (Switch Ports)

Pressure switches and transducers such as the high-pressure cutout, fan switch, and trinary switch are often mounted on Schrader-type ports with a valve depressor. On many systems the switch can then be unscrewed without recovering the charge, because the valve closes as the switch comes out. Confirm in service information before removing any switch. Some switches thread directly into the line and require recovery first. Replace the switch O-ring or seal and leak-test afterward.

Filters and Screens

• Inline filters can be added to the liquid line (or the suction line ahead of the compressor) after a failure, to catch remaining debris. Install them in the flow direction marked on the housing.
• Screens on orifice tubes, expansion-valve inlets, and some receiver outlets trap debris. A plugged screen causes a restriction with frost or a temperature drop at that point.
• A filter or screen that keeps plugging means debris is still circulating. Find and clean up the source.

After Any Line Repair

Recover, repair, replace the receiver-drier or accumulator if the system was opened long enough to admit moisture, evacuate to a deep vacuum and verify it holds, charge by weight, then leak-test all joints that were disturbed.