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Heater Core replacement

12861 Views 44 Replies 23 Participants Last post by  AAIIIC
Heater cores on early 90s Cadillacs are a weak point. Let's all share our experiences on what we have tried, sucessfully and unsuccessfully to resolve issues and get the good heat back. Perhaps this thread might make a good "Sticky".

I have a 1993 DeVille and a 1992 Seville and I've been into the heater cores a couple times. These are my experiences.

For starters, we have owned our 1993 DeVille since 1998. From day one it never threw heat of any measure. Living in Wisconsin and traveling to Minnesota regularly, it is not a good thing to have a weak heater. I can remember driving from St Paul and after 3 hours of driving (with blankets on our legs) it would still be chilly (not freezing, but annoyingly uncomfortable) in the car. On top of that neither of our cars have heated seats!

Finally, 2 years ago I removed the heater core in the DeVille and attempted a fix. I did the drain-cleaner trick which I have used successfully on other heater cores in the past. That is, ya use drain cleaner to clean out the deposits in the heater core. Afterwards, it was better but not significantly. I ended up buying a new one from Cadillac for about $90. The original heater core is an aluminum unit with plastic end-caps. Aftermarket copper replacements are available for less but aluminum has a better heat transfer cooefficient than copper. The car has thrown a good amount of heat ever since. It's a shame I didn't work on it right away after we bought it.

Our Seville (1992) never threw good heat either. We have only owned it a few years, now and since we do not typically drive it in the winter, or very seldom, the lack of a strong heater was tollerable. Until now. Recently, I have been driving it in the winter as I am in the process of repainting our 1993 DeVille. The temp has been hovering around 0 or into the low teens for the last two weeks. It has been cold and I had enough. Last week I removed the heater core (fortunately they're easy to remove on these cars) and gave it the drian-cleaner flush treatment. This time I performed several applications using drain cleaner (crystals) and was more careful than I was on the DeVille project to swish the drain cleaner around inside the heater core to get the ends and portion between the inlet and outlet. A lot of black colored and chunky deposits were flushed out. It would get so hot, in fact, that I could barely hold onto it. I was using rubber (PVC actually) gloves. Afterwards it looked like brand spanking new inside. But then again, so did the DeVille heater core when I finished cleaning that one.

The proof is in the pudding (whatever that means) and the fact is, the additional time flushing it out with drain cleaner was a successfull fix. It works great now, throws a good deal of heat! Before there was scant heat in cold temperatures even when set at 90 degrees. Now, I get wonderful heat and it keeps the interior toasty warm and comfortable. I keep it set at 73 degrees. This time it was a success.

Heater Core Removal Steps:
Removing the heater core from this year of vehicle is easy. Remove the glove box. Before going on any further, turn the ignition on and move your heat/cool setting from 60 degrees to 90 degrees and see that the actuator moves the damper door on the heater box. If it moves, then you know that's not the problem and the heater core probably is. Proceed by removing the computer and pull it away for access.

[It would probably be a very good idea to remove the air bag fuse and separate the yellow connector under the steering column before digging into the electrical components like the book says.]

Continue by removing the AC/Heat mixing damper rod (the little metal rod) by CAREFULLY lifting up the threaded end out of the plastic clip. Then remove the heater box cover (2 screws) and move it to the side to gain access to the heater core. Move to the engine compartment and remove the hose clamps that secure the hoses to the heater core. They're against the firewall and you probably won't even be able to reach them. Use a long screwdriver. On our DeVille, there are spring clips instead of threaded hose clamps and I had to make a special tool in order to remove these spring clips. Again, it's tight in there and its unlikely you will be able to get your hand in there. I will try to post a picture of the tool for others to see on my website. Then, take a long, strout screwdriver or prybar and carefully pry the hose off the heater core inlet and outlet ports. Oh yeah, put a drain pan below the car to catch the antifreeze and also remove the radiator cap.

Go back to the inside of the car and remove the two bolts that secure the heater core to the heater box. You should then be able to remove the heater core pretty easily and pull it from the car. Do your repair or replace the heater core with a new one.

The installation is the reverse of removal. The only thing of note is once you get everything back in place (except the glove box), you need to be sure the little metal hot/cold damper actuating rod is adjusted properly. To do this, turn the ignition on (don't start the car) and turn the heat to 90 degrees. Wait a minute to allow the actuator to move all the way to the end of it's stoke. When it's there, it should be pointing all the way towards the PCM computer on the Rt side of the car. Pull the rod over to the connector and put a little tension on the rod and then snap it into the plastic connector on the actuator arm. Use EXTREME care and support the plastic actuator arm and don't break it! That would be a costly mistake. When I say apply some tension to the rod, I mean you want to be sure that when the door is fully closed there is some tension on the arm to hold the door in it's closed position.

Once you have done this, change your climate control setting to it's lowest or coldest setting 60 degrees and watch the arm stroke the opposite direction. If it doesn't move, check your wiring. Once it reaches the other side check for a slight amount of tension holding the mixing damper door shut. If this is right, you have it adjusted properly and you can put the glove box back in, fill the radiator and try out the heat. You're done!

What are your experiences with your car's heater?

Mark G
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Do a search. There are a few different posts about it and even if they don't end up being for your exact year they should still help you.
Procedure to replace a heater core in a 96DeVille:

1) Remove the negative terminal on the battery. You're going to be working around the passanger airbag and pulling electrical connectors of the A/C Programer. Good idea to kill the power.

2) Open glove box and observe the access door in the rear. You are going to open this. Give a good tug on the left end of the door and pull straight in. Give it a good one, it will pop open. Un-clip the airbag connector that's clipped in place.

3) Remove the glove box. Six torque screws hold the glove box in place. Four on the front [open the door first] and two on the glove box floor. If you don't have appropriate torque drive a hex drive will work [especially on those two on the box floor]. Don't worry about the electricl wires plgged into the left end of the box. Pull straight out and then rotate the assembly off to the left out of the way - no need to unhook all that stuff and tempt Murphy.

Nice thing is that you will be working though this opening and not standing on your head under the dash, most of the time!

4) Under the dash panel is a black plastic sound panel that needs to be removed. Its held in place by three 7mm screw nuts along the near edge. Remove these and the panel will drop down and pull out. If your old core sprung a leak this caught some of the coolant - take care and wash the foam on the rear of the panel. Hot water and soap in the kitchen sink will do.

5) You are going to want to protect the left front fender while you attempt pulling and installing the heater hoses. Once done, pull the heater hoses on the engine side of the fire wall. This is a pain in that there's hardly enough room and it is a two handed operation. Take care not to damage the hoses - new sets are dear. Also watch out for all those vacume lines and electric lines that are right there crowded in and around. Keep in mind you are going to hook these up to the new core. That will prove more difficult.

6) Back inside the cabin take a look inside the glove box opening. Tucked away back to the right of things, way up there, you will see a silver box with colored vacume lines attached to its bracket. This is the A/C Programer. Look closely and you will see a single screw nut on the right end of the bracket. This is what you need to remove. Take care and do not drop that screw nut. You will never find it and will need to replace or, as I did, improvise to get it back together.

With the screw nut removed the whole A/C Programer unit wil be free and you will be able to wiggle it out and down. Move connectors as needed and take care with those vacume lines. Do not try to pull these. Don't want to think about trying to replace that stuff and remember Murphy. With the unit down flip it and pull the electric connectors off the progamers bottom edge. They release with a clip connection on the back side - pinch and pull.

Object here is to make room to the right side of that black plastic box you're seeing. This is the heater box.

7) Look on top of the heater box. You will see a control rod. Un-clip this on the right side, where it clips onto a white plastic control piece. All you need is a screwdriver under the rod on the right end and twist to pop it out of its groved retainer.

8) The heater box is split vertically in its center and is held together by two screw nuts. One you can see by looking through the glove box opening, the other is about six inches below it. Remove these and open the heater box to the right to expose the heater core.

9) The core is held in place by an end bracket secured by two screw nuts. Remove this bracket and give the core a good wiggle and pull it out and down into the cabin as best you can. You are pulling the hose stubs through the fire wall and it will come out.

10) The replacement core should come with a new bracket and air seals. Looking inside the box, where the core was you will see four strips of foam surrounding the opening. These should be replaced. It's tight in there, but take your time.

11) Install the new core once the air seals are replaced and secure it with the new bracket. Then go out and hook up those heater hoses. You are going to be pushing and twisting, but get them home and tighten the clamps well. With this done go back inside and give the core a good push towards the firewall. Recheck the bracket. The core should be in there firm as a rock.

12) All that's left is to put things back together in reverse of taking it apart.

Not bad 'eh? Book says two hour job, good luck. I've attached a pic showing how my core failed. Not what I expected.


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Nice write up Krimson. :thumbsup: I copied it to the Tech Tips section.
I installed a new heater core in my 92 deville yesterday.
I flushed the cooling system and made sure water would flow through the new core.
I installed a new "T' with the restrictor on the side next to the heater.
New 195 degree thermostat. Coolant pellets and distilled water after the antifreeze.
I still got no heat!!!
I watched the heat controller work when I changed the heat, I even undid the connecting rod and moved the door by hand.
ANYBODY got an idea what is going on.
I have bled the air out of the system, and even put water in the core when filling the radiator.
Was it the air mix door you where moving? Where the hoses to & from the heater core hot? Are you sure that the restrictor is in the proper leg (I forget which one)?
The door I was moving was right behind the heater core.
I just went out and started the car and turned the heater on and it worked till the thermostat opened, then it just blew cold air.
The restrictor is the way the old one was turned, but the heater didn't work then either.
O rileys has the restrictor for about $10.
The hose comeing from the thermostat housing is hot, the other hose cooled off after the thermostat opened.
Maybe it has an air pocket in there.
Yeah, might be air in the system. Sounds like coolant is not circulating through the core.
I drove the car today and the heater works great.
Must have been air in the system.
Thanks Ranger.
How do you get the air out of the system afterwards ?
Just rev the engine to 3000 - 4000 RPM and it will purge itself of air.
I just replaced the heater core in my 95 el dorado today. I got started around 8am, took everything apart, grabbed breakfast, picked up the new heater core, put it all put back together finishing up around noon. Thank you for the post, I'm sure I'd still be working on it had you not shared your expertise.
I just replaced the heater core in my 95 el dorado today. I got started around 8am, took everything apart, grabbed breakfast, picked up the new heater core, put it all put back together finishing up around noon. Thank you for the post, I'm sure I'd still be working on it had you not shared your expertise.
Not bad. I might want to put you to work sometime.
How can you make sure the heater core needs to be changed?
If it leaks, it needs to be changed. Otherwise, it doesn't.
Where do I get the foam insulator mentioned in the write up? It says to replace a strip of foam. Do I just use household foam tape? I hope I can get the 15 yr old heater hoses off without damaging. Its really cold right now, should I heat them up with a heat gun first?

Also, my heater core is all plugged up (probably from those pesky pellets!). I suppose I could flush it, but I dont mind spending the day and $50 for a new one, does this indicate that I am insane?

Thanks for the excellent write-up, I had just got the glove box out and the sound panel off, but couldnt quite see how to access that core. The service manual is not very clear on this repair. Now I know just what to do.
That is a good write up. This is why I am now supporting this site. My dealership wants $550. + to do this :bonkers: I plan on giving it a shot. Thanks, krimson-cardinal! 1 Question, I was searching this topic earlier and I think I saw something about knocking the hose's off from the firewall during removal, or something to that effect and he had a tool with a long do-hicky w/ a triger..does this ring a bell to anyone?
I think you are talking about a hose clamp tool on a flexible cable for those hard to reach places. Something like this?
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