G-body heater core replacement
 

semi-pro method for replacing a g-body heater core

Before we go any further, I'd like to thank Scott Keller and Tom Lorek for the write-up they did. That one is on the GN-T-Type site here

Their instructions allowed me to get started on my project. I would have been lost without their page.

Ok. Let's get started.

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Disconnect underhood light. (2-7mm screws)

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Remove seal from edge of cowl. If this is the way it left the factory it should just lift off the cowl lip (no adhesive.)

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Disconnect electrical connector on A/C drier and remove A/C solenoid from top section of A/C-heater housing. (2-7mm screws)

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Disconnect 3 electrical connections on the blower motor and remove blower vent tube. The wiring harness should now be free. Move it out of your way.

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The write-up on the GN page suggests removing the wiper arms. I found out that it's easier to position the arms to the vertical (turn the wipers on and then switch the key off when they're vertical.)

Then remove the wiper rests and the screws holding the lower windshield trim in place, and remove the trim piece. CAUTION: This part is very delicate and can be easily kinked or damaged. I used a screwdriver to loosen the sealant from the back of the trim and then moved it out of the way.

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Remove blower motor. (5-1/4" screws and 1-7mm screw for ground tab).
Remove cowl vent. (6-7mm screws) Note that one screw may have a washer on it.

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Remove upper A/C-heater housing. (4-10mm screws and 10-1/4 screws.) I had to pry the housing loose from the old sealant.
Take care at this point not to rush the removal of the housing, it will come out easily when done properly.

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The heater core should be easy to remove at this point. One screw holds it in with a bracket and ground strap at the top, and a clip holds it in at the bottom.

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Remove and replace the heater hoses carefully. I used a little Vaseline to help slip the hoses onto the new core fittings.

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Here's the drain door at the bottom of the plenum. I vacuumed out all the trash and stuff and cleaned it to make sure that any water that gets in here can drain easily.

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Then I made a dam of RTV to keep any water from entering the air door, especially if the car is parked on an incline.

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I sealed the upper housing with black silicone (because that's what I had on hand.) You may want to get some windshield sealant at your local parts store.

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I also took the opportunity to clean all the plastic parts and re-paint the lower windshield trim and heater motor.

This worked very well for me, especially considering that it was my first time doing this job. It wasn't nearly as hard as I thought it was going to be. Good Luck with your project.

i wish mine were easy to get to like yours my heater core is in the dash. oh how did you know if you needed a heater core?? a mass coolent leak or some thing else??

the one on my 1975 caprice was on the inside also, after I tore the hell out of the cardboard glove box I was able to replace it but couldn't use the glove box!!

3rd gen monte's r the same way guys.

Nice rite up bud.....I have done several of these!

Man Im new to this forum and really appreciate this write up. My wife just inherited a 1986 ss that needs some work. Its gotta have a heater core. Its leaking antifreeze in the floorboard, and fogging up windows. I just bypassed the heater core for now but have no heat. The car has been sitting parked since the 90's. Im glad to see that I dont have to take the whole dash out to change core. Its a really nice mc, only has 66k actual miles, but I have too many projects goin on right now and dont really ahve the time to dedicate to it right now.

Hi, just did this, and if I would have taken my time I wouldnt have cracked the cover for the box. Does anyone know thw part number for a new one. My car is an 87 and is original, so I need the original cover..with air. Thanks

Mine cracked on my old car and I taped it up with aluminum tape. I found it in the furnace dept. at home depot.

sorry i missed this is it just the top cover? if so i may be able to help you out, let me dig around i pulled my whole unit out and it will not be going back in the car, if i have not trashed it yet you can have it for the cost of shiping

Just removed everything from my 84 CL today but accidentally crack my cover pretty bad. Does anyone else happen to have one sitting around? Can Paypal you the money. Thanks!