Heater Core

This procedure removes and replaces the heater core in a 1994-2007 Dodge Ram 2500 with the 5.9L Cummins diesel engine, requiring extensive dashboard disassembly.

Warnings

Tools required

Parts

• Heater core × 1 — Use OEM specification
• Heater core seals/gaskets × 1 — Typically included with heater core
• Heater hose clamps × 2 — Replace if worn
• Coolant (ethylene glycol) × 2 — HOAT or conventional per year

Fluids

• Ethylene glycol 50/50 (green conventional early, HOAT later) — 2 qt

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 and wait 2 minutes for airbag system to discharge
4. Remove driver and passenger seats for better access (4 bolts each)
5. Place drain pan under radiator and open drain petcock to drain cooling system
6. Photograph dashboard and center console from multiple angles for reference
7. Cover steering column and seats with towels to protect from coolant drips

Procedure

1. 1

   Drain cooling system and disconnect heater hoses
   Open radiator drain petcock and drain coolant into appropriate container. Once drained, locate the two heater hoses at the firewall on the passenger side of the engine bay. Use hose clamp pliers to release the spring clamps and slide them back on the hoses. Disconnect both heater hoses from the heater core tubes. Cap or plug the core tubes to prevent residual coolant spillage.
   ⚠Residual coolant will drain from hoses and core tubes. Have towels ready to catch spillage.
   Torque spec

   Drain Petcock7 Nm (5 lb-ft)
2. 2

   Remove instrument cluster and center console
   Remove the instrument cluster bezel by removing retaining screws around the perimeter. Pull cluster bezel forward and disconnect any electrical connectors. Remove the instrument cluster mounting screws and pull cluster forward. Disconnect the electrical harness connectors from the cluster (the speedometer is electronic; there is no mechanical cable). Remove center console shifter bezel, then remove center console mounting screws and lift console out. Disconnect electrical connections as needed.
   Torque spec

   Dashboard Screws3 Nm (2 lb-ft)
3. 3

   Remove steering column and lower dashboard components
   Remove the steering column cover screws and separate upper and lower column covers. Lower the steering column by loosening the column support bracket fasteners (do not remove completely, just lower for clearance); verify count and locations against the factory service manual. Remove the lower dashboard knee bolster panel and side trim panels. Remove all dashboard mounting screws along the lower edge and sides.
4. 4

   Disconnect dashboard electrical connections and HVAC controls
   Working from both driver and passenger sides, systematically disconnect all electrical connectors from the dashboard harness. Label each connector with tape for reassembly reference. Disconnect the HVAC control cables from the heater housing by releasing the cable clips. Disconnect vacuum lines from the HVAC controls and vacuum reservoir (note: on the Cummins diesel, HVAC vacuum is supplied by an engine-driven vacuum pump rather than manifold vacuum).
   ℹ️Take photos of vacuum line routing before disconnection. Incorrect routing will cause blend door problems.
5. 5

   Remove upper dashboard mounting and antenna/wiring
   From the passenger side, remove the glove box assembly. Remove the upper dashboard mounting bolts accessible through the glove box opening and along the windshield area. Disconnect the antenna cable from the radio. Remove any remaining dashboard mounting bolts at the A-pillars and center support bracket. With an assistant, carefully lift and remove the entire dashboard assembly from the vehicle.
   ⚠Dashboard is heavy and awkward. Use an assistant to prevent damage to components or injury.
6. 6

   Remove HVAC housing assembly from firewall
   With the dashboard removed, locate the HVAC housing mounted to the firewall. Disconnect the remaining electrical connections to the blower motor and actuators. Remove the HVAC housing mounting nuts from the firewall (accessible from both engine bay and interior). Carefully pull the HVAC housing away from the firewall studs and lower it from the vehicle. The unit is bulky; work it through the opening carefully.
   ℹ️Note the position of any foam seals or gaskets between the housing and firewall for reinstallation.
7. 7

   Disassemble HVAC housing to access heater core
   Place the HVAC housing on a clean work surface. Remove the housing cover screws around the perimeter of the case. Carefully separate the housing halves. The heater core is mounted in the lower section with a retaining bracket. Remove the heater core mounting screws/bracket. Note the position of foam seals around the heater core.
   ⚠Residual coolant will drain from the old heater core. Have a drain pan ready.
   Torque spec

   Heater Core Mounting8 Nm (6 lb-ft)
8. 8

   Install new heater core and reassemble housing
   Transfer any foam seals or gaskets to the new heater core if they are reusable, otherwise use new seals provided with the core. Install the new heater core into the lower housing section in the same orientation as the old unit. Install the heater core mounting bracket and secure with screws to the specified torque. Carefully align the upper and lower housing halves and install cover screws to specification.
   Torque spec

   Heater Core Mounting8 Nm (6 lb-ft)
9. 9

   Reinstall HVAC housing to firewall
   Position the reassembled HVAC housing into the vehicle and align it with the firewall mounting studs. Ensure the heater core tubes protrude through the firewall opening correctly. Install mounting nuts and tighten evenly. Reconnect all electrical connections to the blower motor, blend door actuators, and any sensors. Verify all connections are secure.
10. 10

    Reinstall dashboard assembly
    With an assistant, carefully position the dashboard assembly into the vehicle. Align all mounting points and start all mounting bolts by hand before tightening. Install dashboard mounting bolts at A-pillars, center support, and along the windshield to specification. Reconnect all electrical connectors using your reference photos and labels. Reconnect HVAC control cables and vacuum lines in their original routing. Reinstall the steering column to proper height and tighten mounting nuts.
    Torque spec

    Dashboard Screws3 Nm (2 lb-ft)
11. 11

    Reinstall interior components
    Reinstall the instrument cluster and reconnect the electrical harness and speedometer cable. Secure cluster with mounting screws. Install the instrument cluster bezel. Reinstall the center console, shifter bezel, and all lower dashboard panels and trim pieces. Ensure all retaining clips and screws are properly secured. Reinstall any interior trim removed for access.
    Torque spec

    Dashboard Screws3 Nm (2 lb-ft)
12. 12

    Connect heater hoses and refill cooling system
    In the engine bay, reinstall the heater hose clamps on both heater hoses (replace only if the spring clamps are weak or corroded). Connect both heater hoses to the heater core tubes at the firewall, ensuring they are fully seated. Position and tighten hose clamps to specification. Close the radiator drain petcock to specification (hand tight). Fill the cooling system with the appropriate coolant mixture (Chrysler HOAT/G-05 for approximately 2002-and-later models, conventional green ethylene glycol for earlier models — verify the correct type for your specific model year) to the proper level.
    ℹ️Use the correct coolant type for your model year. Mixing coolant types can cause system damage.
    Torque spec

    Heater Hose Clamps3 Nm (2 lb-ft)

    Drain Petcock7 Nm (5 lb-ft)
13. 13

    Bleed cooling system and check operation
    Reconnect the negative battery cable. Start the engine and allow it to reach operating temperature with the heater controls set to maximum heat and fan speed. Monitor coolant level and add as needed as air bleeds from the system. Check for leaks at heater hose connections and around the firewall penetration. Verify hot air flows from all dashboard vents when heater is on. Check that temperature blend and air distribution controls operate correctly through all positions.
    ⚠Monitor engine temperature gauge closely during bleeding process. Shut down immediately if overheating occurs.

Reassembly

1. Reinstall components in reverse order of removal, referring to photographs taken during disassembly
2. Ensure all electrical connections are secure and properly seated
3. Verify all dashboard mounting bolts are tightened to specification to prevent rattles
4. Check operation of all dashboard controls, gauges, and accessories before final testing
5. Double-check coolant level after initial test drive and add if necessary

Verification

• Start engine and verify hot air flows from all dashboard vents when heater is set to maximum
• Check that temperature control operates smoothly from cold to hot with appropriate air temperature change
• Verify all air distribution modes (defrost, floor, panel) operate correctly
• Inspect for coolant leaks at heater hose connections and inside vehicle (check carpet under dashboard for wetness)
• Confirm no coolant odor inside cabin during operation
• Test that all dashboard gauges, controls, and accessories function normally
• Check coolant level after engine reaches operating temperature and top off if needed
• Verify engine maintains normal operating temperature without overheating

Related trouble codes on this vehicle

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