i just done this myself, and unless you have alot of patience, i wouldn't recommend it, you must remove the entire dashboard, drop the steering column, and detach heater hoses, a/c lines on fire wall, then remove a/c heater box in passenger compartment, good luck! beside the millions of screw and wire harnesses, it was a learning experience
the heater core is bad
Remove the water supply hoses from your 2002 Dodge Ram 1500 heater core. Remove the heater core retaining bolts. Reverse the process to install the new heater core.
You remove heater core in doge neon by smashing the windows then taking off the doors so you can get th the heater core then you get a crowbar and rip it out (if this destroys your dodge neon then your car isn't a real dodge neon).
Heater core is on the passenger side behind the glove box, this is also the location of the air conditioner evaporator core.. they should be in the same housing.
Drain the water from your Dodge Ram truck cooling system. Remove the water lines from the heater core. Remove the heater core retaining bolts. Reverse the process to install the new heater core.
Remove the dash!
Inside the dash, in the HVAC housing. The entire dash has to be removed to access.
Drain the water from the cooling system. Remove the water hose from the heater core. Remove the heater core retaining bolts. Reverse the process to install the new heater core.
From the Dodge forums. Drain the coolant, disconnect the surge tank to heater pipe line, and the heater core to heater pipe line, remove the drivers side engine mount, and the starter, and unbolt the heater pipe from the engine-transmission bolt. Remove the clamp from the short hose at the thermostat housing, and pull the pipe out.
Probably the evaporator core has mould on it and needs to be cleaned.
You need to recover the R134 charge, remove the whole dashboard, then remove the a/c heater box to get to the heater core. The heater core should be accessible right next to the gas pedal. No dash removal is necessary.
Removal of the passenger airbag will not provide access to the heater core. The entire dash and HVAC housing need removed.