The heater core is up in, and under the dash. To remove it is a rather extensive job. I'd recomend a shop manuaul. The center consol, radio, heater control, glove box, and possibly part of the steering column will need to be removed first. The hoses on the fire wall in the engine compartment will need to be disconnected. If the unit also has A/C, there are a few other items to be considered. I'd figure on about 8 hours for the entire job. The replacement heater core only costs about $40 to $50. The expense is for the labor involved.
The heater core is above/behind the air outlet for the floor. The heater core can be tricky to get out and take a bit of time and patience. Be sure it's the heater core before you take on this task. It will save you a lot of frustration. If your car gets hot but you still blow cold air when temp setting is in hot then you have either low coolant, a stuck thermostat, or a blocked heater core. If your interior floor is damp near the center front of the floor, then you most likely have a leaky heater core.
Geo heater coreThe dashboard and instrument cluster have to come out to gain accsess to heater box (white box next to a/c).The heater box splits in half. Remove metal tube to gain accsess. AnswerI have water dripping from under the dash on the passenger side of my 1994 Yukon . Could that be my heater core and is that an easy fix ?