AC Hose - Low Side

Replace the low-side AC hose on a 2007 Ram 3500 with 5.9L Cummins diesel engine, including proper evacuation and recharge of the AC system.

Warnings

Tools required

Parts

• AC low-side hose assembly × 1 — Use OEM specification
• AC line O-rings × 4 — Use OEM specification or AC fitting kit
• PAG oil for AC system × 1 — Match original viscosity specification

Fluids

• R-134a

Preparation

1. Park vehicle on level surface and allow engine to cool completely for at least 2 hours
2. Disconnect negative battery cable to prevent fan cycling during service
3. Verify AC refrigerant type using refrigerant identifier before recovery
4. Position drip pan or absorbent pads under work area to catch residual oil
5. Take note of total system refrigerant capacity for proper recharge (check underhood label)

Procedure

1. 1

   Recover AC refrigerant
   Connect AC recovery machine to service ports. Connect to low-side service port (larger fitting, typically on accumulator or suction line). Recover all refrigerant from the system according to machine instructions. Record amount of refrigerant and oil recovered for proper replacement during recharge.
2. 2

   Locate low-side hose routing
   Trace the low-side (suction) AC hose from the evaporator outlet at the firewall/passenger side to the compressor. Verify component type against the vehicle-specific system layout before proceeding. On the 5.9L Cummins, the hose routes along the passenger side of the engine bay. Note any brackets or clips securing the hose for reinstallation.
3. 3

   Remove hose retaining brackets
   Remove any mounting brackets or clips securing the low-side hose to the body or engine. These may be held with 10mm bolts or push clips. Keep hardware organized for reinstallation in original locations.
4. 4

   Disconnect hose from accumulator
   Disconnect the low-side hose at the evaporator/firewall connection. Depending on the fitting type, use a line wrench for threaded fittings or an AC spring-lock disconnect tool for quick-connect couplings. Be prepared for residual oil to drain. Remove and discard the old O-ring from the fitting.
5. 5

   Disconnect hose from compressor
   Locate the low-side connection on the compressor (suction side - larger fitting). Use line wrench to carefully loosen and remove the fitting. On the Cummins, access may require reaching from above or below depending on hose routing. Remove and discard old O-ring.
6. 6

   Remove old hose assembly
   Carefully extract the old low-side hose from the engine bay, noting the routing path for installation of new hose. Check routing to ensure it does not contact hot exhaust components or moving parts.
7. 7

   Prepare new hose assembly
   Unpack new low-side hose and verify correct fitment by comparing length and fitting types to old hose. Lubricate new O-rings with small amount of PAG oil appropriate for R-134a systems. Install new O-rings onto both ends of new hose fittings.
8. 8

   Install new hose to compressor
   Route new hose into position following original path. Connect the hose to the compressor suction port first, as this is typically the more difficult connection. Hand-tighten the fitting, then use line wrench to snug. Do not overtighten - fittings seal on the O-ring, not by excessive torque.
9. 9

   Install new hose to accumulator
   Connect the other end of the low-side hose to the accumulator/drier. Ensure O-ring is properly seated. Hand-tighten, then snug with line wrench. Verify hose routing does not create any kinks or tight bends.
10. 10

    Reinstall retaining brackets
    Secure the new hose with all original mounting brackets and clips. Ensure hose is properly supported and will not vibrate against other components. Verify clearance from exhaust manifold, drive belts, and other moving parts.
11. 11

    Evacuate AC system
    Connect vacuum pump or AC machine in evacuation mode to service ports. Evacuate system to at least 29 inches of mercury vacuum for minimum 30 minutes. System should hold vacuum without rising, indicating no leaks. If vacuum does not hold, locate and repair leak before proceeding.
12. 12

    Recharge AC system
    Using AC machine, add refrigerant oil to compensate for amount lost, based on the measured oil recovered plus the FSM-specified allocation for the replaced component (typically about 1 oz for a hose). Recharge system with R-134a to the exact capacity specified on the underhood label or in the factory service manual for this vehicle. Do not rely on a generic estimate. Monitor pressures during recharge to ensure proper fill.
13. 13

    Reconnect battery and test system
    Reconnect negative battery cable. Start engine and allow to idle. Turn AC to maximum cold and high blower. Monitor low and high side pressures while system operates. Check all connections for leaks using electronic leak detector or soap solution. Low side pressure should be approximately 25-35 PSI at idle with ambient temperature around 70-80°F.

Reassembly

1. Verify all AC line connections are secure and properly routed with no kinks or contact points
2. Confirm all mounting brackets and clips are reinstalled to prevent vibration
3. Double-check clearance between hose and hot exhaust components or moving parts like belts

Verification

• Run AC system for at least 10 minutes and verify cold air output at vents (typically 40-50°F colder than ambient)
• Monitor AC pressures with gauges - low side should be 25-40 PSI, high side should be 200-250 PSI at normal operating temperature
• Use leak detector to check all connection points for refrigerant leaks, especially new hose connections
• Verify compressor clutch engages and disengages properly
• Check that hose does not contact any moving parts or hot components during engine operation
• Test AC performance under various conditions (idle, high RPM, maximum cooling setting)

More procedures for this vehicle