How To Install Heater Core

step 2: remove passenger side kick panel. Be careful of the speaker and wires. 

step3: remove the passenger side dash bezel that is below the glove box. Be carfeul of the courtesy light 

step 4: remove drivers side dash bezels, below the column. Be careful of the courtesy light. You will also see some Yellow wires, keep those in mind for the next step. 

step 5: disconnect the negative terminal on the battery. Now back under the dash. Follow the yellow wires and you will see a 3 amp inline fuse back by the firewall. Pull that and follow the yellow wires up to the steering column. Disconnect the plug from the wire that goes up into the column. This disables your airbag so you don't accidentally deploy it.
Step 6: Raise and support the car. Remove the hoses to the core. Remove the 90 degree fitting on the drain to the left of the hoses (if you are facing the firewall). Lower the car back to ground. It makes it harder to work with it elevated I found. 

Step 7: Remove the air duct plenum. There are only two screws about in the middle to remove. Be sure to remove the the small flexible ducts at the top of the plenum on both sides. Working from the passenger side. Pull the carpet back and you WILL see where the duct goes in to floor and connects to the fresh air intake duct. Work out the duct to the PASSENGER SIDE OF THE CAR. It's kind of a pain but if you take your time you will get it out and hopefully not crack it into pieces. 

Step 8: remove the screws around the heater core cover. The ones near the firewall were a bit of a pain to remove and there is in the middle towards the firewall over the openning of the fresh air intake duct. (I left this screw out when i replaced everything :P) Now work out the cover out and to the passenger side of the car. be patient and careful. it's not as much of a pain as the duct was. **There is a drain penetrating the firewall, you will need to pull the cover away from the firewall so you don't break off the drain piece or the cover itself.**

Step 9: Now you got your eyes on the prize! Top and bottom of the core is the bracket the holds it in place. Remove those four screws and remove the core

Step 10: Install the new core. HOPEFULLY you bought an all aluminum unit instead of the piece of crud aluminum and ABS plastic unit that came installed originally. (HEY G.M.! IF YOU CHEAPSKATES WOULD HAVE USED AN ALL ALUMINUM UNIT, IT WOULD SAVE YOUR CUSTOMERS AND SERVICE TECHS FROM DOING THIS AT ALL.) Work the new core in thru the passenger side, and install the holding brackets.

Step 11: Reconnect the hoses and fill the radiator back with mixed antifreeze. There is an air bleed port on top of the thermostat housing. Use a 7 mm wrench to open the bleeder, fill the reservoir until you see fluid coming out of the air bleed port. Close the port and look for leaks at your new heater core. Periodically open the bleed port and refill the reservoir as necessary 

Step 12: Reconnect the battery. Start the car and turn your heater on to the max settings. ***The airbag being disconnected will set off the MIL on the dash. Don't freak it will turn off when you get everything back to together.*** Get the car to where the temp stabilizes and check for leaks again. Now turn the climate control to off and let the engine heat up until you hear the cooling fan click on. Turn off the car at this point and look for leaks again. When it reaches the point the fan turns on, that is when it is normally going to be the hottest and highest pressure on the system. THE POINT OF ALL THIS IS TO FIND LEAKS AND SEE IF THE NEW CORE IS GOOD TO HOLD WATER BEFORE YOU PUT EVERYTHING BACK TOGETHER.

Step 13: Once you are satisfied everything is good to go. Disconnect the battery again and reverse the removal process until you got your interior back together. Be careful and patient putting the cover and ducting in. By now hopefully you haven't spent a whole lot of time doing the project and your whole day hasn't been killed working on a car. :P ***Dont forget to replace the 90 degree fitting on drain in the engine compartment and airbag wires***

You will be working in pretty contorted positions and I am pretty sore from all the stretching and twisting. If you got time, remove the seats. Would make a more comfortable and roomier working area. It was a cool dry day and was getting alot of static build up from moving around on the carpet. I was slightly worried if i touched the airbag wires inadvertently I would sparked to the wires. Then I would be installing a new airbag next! The odds of that were pretty unlikely but airbags deploy with very minimal voltage. A ohmmeter on the wrong setting can set them off I have been told. Also, if you got a friend who can help you. Have one do it. The two of you can work from both sides instead of you alone getting in and out, up and down from the car or floorboard.