AC Hose - Low Side

This procedure replaces the low-side AC hose on a 1994-2007 Dodge Ram 2500 with the 5.9L Cummins diesel engine, including refrigerant recovery, hose replacement, and system recharge.

Warnings

Tools required

Parts

• AC low-side hose assembly × 1 — Use OEM or quality aftermarket for proper fit
• AC line O-rings × 4 — Green HNBR R-134a compatible O-rings
• PAG oil for AC system × 1 — PAG 46 or 100 depending on compressor type

Fluids

• R-134a refrigerant

Preparation

1. Park vehicle on level surface and engage parking brake
2. Allow engine to cool completely (minimum 2 hours)
3. Disconnect negative battery cable to prevent fan cycling during work
4. Have AC system professionally evacuated and refrigerant recovered using approved recovery equipment. Record amount of refrigerant removed for recharge
5. Locate low-side AC hose running from accumulator/drier near firewall to compressor on passenger side of engine
6. Place drip pan under work area to catch residual refrigerant oil

Procedure

1. 1

   Access low-side hose at compressor
   From passenger side of engine bay, locate the AC compressor mounted low on the engine block. Identify the low-side hose connection at the compressor suction port (larger diameter fitting). Clean area around fitting with shop towel to prevent contamination. The low-side connection is typically the rear-most fitting on the compressor.
2. 2

   Disconnect hose from compressor
   Using appropriate flare nut wrench, carefully loosen the low-side hose fitting at the compressor. Hold compressor port with backup wrench to prevent turning the port assembly. Once loose, unthread fitting by hand and pull hose away from compressor. Inspect and discard old O-rings. Cap or plug compressor port immediately to prevent contamination.
   ⚠If any residual pressure is present (system was not properly evacuated), refrigerant will discharge. Stop and have system properly recovered.
3. 3

   Access accumulator/drier connection
   Trace low-side (suction) hose from compressor to the evaporator outlet connection at the firewall on the passenger side. This system uses a thermal expansion valve (TXV) with a receiver-drier on the high side, so the low-side hose connects the evaporator outlet to the compressor suction port. Note any mounting brackets or clips securing hose along its route. Remove any clips or brackets as needed for hose clearance.
4. 4

   Disconnect hose from accumulator
   Using flare nut wrench, loosen the low-side hose fitting at the evaporator outlet connection near the firewall. Use backup wrench on the evaporator line fitting to prevent turning. Unthread fitting completely and separate hose. Inspect and discard old O-rings. Cap or plug the port immediately to prevent moisture intrusion and contamination.
5. 5

   Remove old hose assembly
   Carefully extract old low-side hose from engine bay, noting exact routing path around engine components, wiring harnesses, and frame members. Take photos if needed for reference. Remove any remaining mounting clips or brackets attached to old hose. Check for any damaged or missing mounting hardware.
6. 6

   Prepare new hose and fittings
   Unpack new low-side hose and compare to old hose to verify correct length and fitting orientation. Install new O-ring onto each end of new hose (typically 1 O-ring per fitting). Verify quantity against the old hose connections. Lightly lubricate new O-rings with appropriate PAG oil (PAG 46 or 100 based on compressor specification). Apply small amount of PAG oil to fitting threads. Do not over-oil as excess can contaminate system.
7. 7

   Route and position new hose
   Route new low-side hose through engine bay following exact path of old hose. Ensure hose does not contact hot exhaust components, sharp edges, or moving parts like belts and pulleys. Position hose so both fittings align with accumulator and compressor ports without tension or binding. Install mounting clips and brackets finger-tight.
8. 8

   Connect hose to accumulator
   Remove cap from accumulator port. Verify port threads are clean and undamaged. Hand-thread new hose fitting onto accumulator outlet port, ensuring O-rings seat properly and fitting threads engage smoothly without cross-threading. Thread fitting until snug by hand.
   Torque spec

   AC Line Fittings20 Nm (15 lb-ft)
9. 9

   Torque accumulator fitting
   Using torque wrench and flare nut wrench, tighten the evaporator line fitting to the manufacturer-specified AC line torque (verify against factory service manual) while holding the evaporator port with a backup wrench. Do not overtighten as this can damage O-rings or aluminum threads.
   Torque spec

   AC Line Fittings20 Nm (15 lb-ft)
10. 10

    Connect hose to compressor
    Remove cap from compressor suction port. Verify port threads are clean and undamaged. Hand-thread new hose fitting onto compressor port, ensuring O-rings seat properly and fitting threads engage smoothly. Thread fitting until snug by hand.
    Torque spec

    AC Line Fittings20 Nm (15 lb-ft)
11. 11

    Torque compressor fitting
    Using torque wrench and flare nut wrench, tighten compressor fitting to 20 Nm (15 lb-ft) while holding compressor port with backup wrench. Verify hose routing has no kinks or tight bends after final tightening. Adjust mounting clips if needed.
    Torque spec

    AC Line Fittings20 Nm (15 lb-ft)
12. 12

    Secure hose routing
    Tighten all mounting clips and brackets along hose route. Verify minimum 1-inch clearance from exhaust manifold, turbocharger, and all moving components. Check that hose does not contact radiator hoses, wiring, or sharp edges. Adjust routing as needed for proper clearance.
13. 13

    Vacuum and recharge system
    Reconnect battery negative cable. Connect AC manifold gauges to service ports. Using vacuum pump, evacuate system to 29 inches of mercury (98 kPa vacuum) and hold for minimum 30 minutes to verify no leaks and remove moisture. If vacuum holds steady, recharge system with refrigerant to manufacturer specification (use amount recorded during recovery as baseline). Add PAG oil if required per compressor specifications.

Reassembly

1. Verify all AC line fittings are torqued to specification and O-rings are properly seated
2. Confirm hose routing provides adequate clearance from all hot and moving components
3. Ensure all mounting clips and brackets are secured

Verification

• Start engine and set AC to maximum cold with blower on high
• Using manifold gauges, verify low-side pressure is 25-45 PSI at idle (varies with ambient temperature)
• Check for cold air output from dash vents (38-42°F at vent in recirculation mode)
• Inspect all fittings for refrigerant leaks using electronic leak detector or soap solution
• Verify no unusual noises from compressor or hose vibration
• Check that low-side hose is cool to touch during operation (should be cold but not frosting)
• Run system for 10-15 minutes and recheck all fittings for leaks
• Verify compressor clutch engages and disengages normally

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