Here is the procedure to repair heater core. This one is fairly easy. It is underdash . If you have any questions just ask
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See Figures 1, 2 and 3
Disconnect the negative battery cable and drain the cooling system.
Raise and support the vehicle safely.
If equipped, remove the rear lateral transaxle strut mount.
Disconnect the drain tube from the heater case.
Detach the heater hoses from the heater core.
Carefully lower the vehicle.
Remove the right and left sound insulators.
Unfasten the steering column opening filler. Disconnect the heater outlet deflector (floor air outlet duct).
Fig. 1: Disconnect the floor air outlet duct
Remove the heater core cover.
Fig. 2: Unfasten the retaining bolts, then remove the heater core cover
Detach the heater core retaining straps (clamps), then remove the heater core.
Fig. 3: Detach the retaining clamps or straps, then remove the heater core
Install the heater core and retaining straps (clamps).
Install the heater core cover.
Reconnect the heater outlet deflector (floor air outlet duct).
Install the right and left sound insulators. Install the steering column opening filler.
Connect the heater hoses (use new heater hose clamps if necessary) to the heater core.
Connect the drain tube to heater case.
Connect the rear lateral transaxle strut mount, if equipped.
Lower the vehicle.
Fill the cooling system and check for leaks. Check heater system for proper operation.