I have a heater core leaking. I was looking for a detailed list to remove and replace the heater core.
Sep 9, 2026 at 11:05 AM
Heater core leaking?
2007 HUMMER H3
BRISTLES
- MEMBER
- 3 POSTS
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This is a big job, I would drain the coolant, disconnect the battery, vacuum down the AC system before you begin. Yes, the heater core on this H3 is inside the HVAC housing, so replacing it requires removing the instrument panel and HVAC module. The A/C refrigerant must be professionally recovered before disconnecting the evaporator lines.
Removal
1. Disconnect the negative battery cable and wait at least two minutes before working around the airbags.
2. Have the A/C refrigerant recovered with approved equipment.
With the engine completely cold, drain the cooling system.
3. Disconnect both heater hoses from the heater-core tubes at the firewall. Plug the hoses and tubes to limit coolant leakage.
4. Disconnect the A/C suction and liquid lines from the evaporator at the firewall. Cap every opening immediately to prevent moisture from entering.
5. Remove the center console and necessary lower dash trim panels.
6. Remove the steering-column trim, disconnect the intermediate shaft as required, support the steering column, and lower or remove it.
7. Remove the instrument cluster, radio/control assembly, glove box, passenger airbag and remaining instrument-panel trim.
8. Label and disconnect the instrument-panel wiring connectors, grounds, antenna lead and HVAC control connections.
9. Support the instrument panel, remove its mounting fasteners and carefully lift the complete panel/carrier from the vehicle. Having a helper is strongly recommended.
10. Disconnect the HVAC electrical connectors, vacuum lines and drain tube.
11. Remove the HVAC housing mounting nuts from the engine-compartment side of the firewall.
12. Remove the interior HVAC housing fasteners and take the housing out of the vehicle.
13. Remove the HVAC housing cover screws and separate the housing carefully.
14. Remove the heater-core retaining bracket and lift out the heater core.
Installation
Install the new core with fresh seals and foam strips, then reverse the removal procedure. Replace the A/C line O-rings with the correct refrigerant-compatible seals lubricated with clean refrigerant oil. Make sure the evaporator drain and all HVAC doors and linkages are correctly positioned before reinstalling the dashboard.
After assembly:
Refill and bleed the cooling system.
Evacuate and recharge the A/C system to the under-hood specification.
Check carefully for coolant and refrigerant leaks.
Verify heat, A/C operation and airflow from every mode.
Confirm that the airbag warning light turns off normally.
Before beginning, pressure-test the cooling system and verify coolant is actually leaking from the heater core or HVAC drain. Leaking heater-hose connections at the firewall can sometimes imitate a failed core. This is a substantial job—typically most of a working day for an experienced technician. Let me know how it goes, here is a video to help with the AC.
https://www.youtube.com/watch?v=4EqdrBVb0sY
Removal
1. Disconnect the negative battery cable and wait at least two minutes before working around the airbags.
2. Have the A/C refrigerant recovered with approved equipment.
With the engine completely cold, drain the cooling system.
3. Disconnect both heater hoses from the heater-core tubes at the firewall. Plug the hoses and tubes to limit coolant leakage.
4. Disconnect the A/C suction and liquid lines from the evaporator at the firewall. Cap every opening immediately to prevent moisture from entering.
5. Remove the center console and necessary lower dash trim panels.
6. Remove the steering-column trim, disconnect the intermediate shaft as required, support the steering column, and lower or remove it.
7. Remove the instrument cluster, radio/control assembly, glove box, passenger airbag and remaining instrument-panel trim.
8. Label and disconnect the instrument-panel wiring connectors, grounds, antenna lead and HVAC control connections.
9. Support the instrument panel, remove its mounting fasteners and carefully lift the complete panel/carrier from the vehicle. Having a helper is strongly recommended.
10. Disconnect the HVAC electrical connectors, vacuum lines and drain tube.
11. Remove the HVAC housing mounting nuts from the engine-compartment side of the firewall.
12. Remove the interior HVAC housing fasteners and take the housing out of the vehicle.
13. Remove the HVAC housing cover screws and separate the housing carefully.
14. Remove the heater-core retaining bracket and lift out the heater core.
Installation
Install the new core with fresh seals and foam strips, then reverse the removal procedure. Replace the A/C line O-rings with the correct refrigerant-compatible seals lubricated with clean refrigerant oil. Make sure the evaporator drain and all HVAC doors and linkages are correctly positioned before reinstalling the dashboard.
After assembly:
Refill and bleed the cooling system.
Evacuate and recharge the A/C system to the under-hood specification.
Check carefully for coolant and refrigerant leaks.
Verify heat, A/C operation and airflow from every mode.
Confirm that the airbag warning light turns off normally.
Before beginning, pressure-test the cooling system and verify coolant is actually leaking from the heater core or HVAC drain. Leaking heater-hose connections at the firewall can sometimes imitate a failed core. This is a substantial job—typically most of a working day for an experienced technician. Let me know how it goes, here is a video to help with the AC.
https://www.youtube.com/watch?v=4EqdrBVb0sY
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Sep 10, 2026 at 9:02 AM
Repair Safety Notice: This information is for general instructional purposes only. Vehicle repair can be dangerous. Verify all information, follow manufacturer service procedures, use proper tools and safety equipment, and consult a qualified repair shop when needed.