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Heater Core replacement

12864 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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Replacing Heater Core 91 DeVille—Any advice?

Up until a few days ago, I was getting warm air out of the passenger side defroster vents, but now, it's just cold air. I've replaced the heater control valve and attempted to flush the core without success, so it looks like I'll have to change out the core (I think it's leaking a little, too). Driving home from work last night, the outside temperature was 35º, and I don't think it was much warmer inside the car.

The local NAPA store has a core for about $50, and I've downloaded a couple of posts from the site on changing out the core, plus I have directions in my shop manual. So I'm going to attempt the job tonight (I drove my Impala today so the Caddy will be cool when I start working on it).

What I'm looking for is any advice from anybody who has done this job. What kinds of problems come up, and how do you solve them? I've seen where access to the hose connections at the core are a problem. What's the simplest way to get to them, disconnect them from the old core and put them on the new one? I've replaced the spring-type hose clamps with screw-on clamps on the other hoses, but I suspect it has spring clamps at the core.

Are any special tools required (or helpful)? How long should the job take? I'll probably take twice as long since I'm not handy with tools. If anybody has any pictures, that'd help, too. I'll try to take some of my own for future reference.
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Re: Replacing Heater Core 91 DeVille—Any advice?

I just did the heater core on my 90 fleetwood tuesday and the only difficult part was removing the spring clamps on the hoses. I have a tool for removing them which has a cable with a sliding jaw clamp at one end and a squeeze grip at the other. I don't know how I could have gotten them off without it. As far as the heater core itself, it was a cake walk.

1. Drain engine cooling system.
2. Heater core inlet/outlet hoses.
3. Right sound insulator.
4. Glove box module.
5. Air mix valve link.
6. Programmer vacuum and electrical connectors.
7. Heater core cover with programmer attached.
8. Heater core retaining screws and heater core.

I took the programmer off the heater core cover just to give me some more room but I don't think you would have to. I also did not drain the cooling system as very little coolant leaks out if you raise the hoses above the engine after removing them. Flat rate on this job is 2.7 hours and I think I had almost 2 into it by the time I was done. Also, when you put it back together you need to adjust the air mix door which is hooked to the threaded rod you removed from the programmer . The procedure is:

1. Remove glove box module.
2. Set temperature on Climate Control Panel (CCP) for 32°C (90°F) . Allow 1 to 2 minutes for programmer arm to travel to maximum heat position.
3. Snap threaded rod from plastic retainer on programmer output arm.
4. Check air mix valve for free travel. Push valve to maximum A/C position, and check for binding.
5. Pre-load air mix valve in maximum heat position by pulling the threaded rod to ensure the valve is sealing. Programmer output arm should be in maximum heat position.
6. Snap threaded rod into plastic retainer on programmer arm. Avoid moving programmer arm or air mix valve.
7. Set temperature on CCP for l6°C (60°F) . Verify the programmer arm and air mix valve travel to the max A/C position.
8. Install glove box module.
These are actually far easier than most heater cores these days. Good Luck!
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Re: Replacing Heater Core 91 DeVille—Any advice?

I agree, the hardest part is getting the heater hoses off at the firewall. ***Be sure your thermostat is working before replacing the core***

I did mine and found out the the stainless steel core was in perfect shape and all I needed was a new thermostat.:(

Good luck.
Re: Replacing Heater Core 91 DeVille—Any advice?

Thanks for the replies.

My back is sore, my hands bruised and cut, but I have heat.

Too me six hours, but four of that was probably getting the hoses off and back on. What a friggin' nightmare! I curse the miserable bastard who invented those godawful spring clamps. Ended up breaking the bottom hose off the old core.

Had a devil of a time putting the hoses on the new core. There's just no room to get your hands in and around the hose. But I managed to get them on enough to put the screw clamps on good and tight.

And when I took the car out, the heat kicked right in (Good thing since is was about 35º). Checked under the hood when I got home; no leaks.

Sheesh, I hope I'm done working on this car for a while.

BTW, Vista Cruiser, I changed out the thermostat when I flushed the cooling system last month. So changing the heater core was a last resort.

One last note: If you have AAA, the discount you get at NAPA can be really good on some parts. It knocked $9 off the price of the heater core, and $14 off the price of new brake pads and rotors.
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Re: Replacing Heater Core 91 DeVille—Any advice?

Out of curiosity, I flushed my core in my 91 (couldn't get my arms into get to the hoses to replace, which was my original plan) and got it opened up (see my thread on how I did it in the tech forum) and was measuring 160-165F out of the floor heater duct with a candy thermometer (don't let the wife see!).

I am curious what a new one pumps out. I ran it on 90 to max it, it was 20 degrees or so out, maybe 30 (was fighting freezing point early on, then it froze)
Re: Replacing Heater Core 91 DeVille—Any advice?

N0DIH said:
Out of curiosity, I flushed my core in my 91 (couldn't get my arms into get to the hoses to replace, which was my original plan) and got it opened up (see my thread on how I did it in the tech forum) and was measuring 160-165F out of the floor heater duct with a candy thermometer (don't let the wife see!).

I am curious what a new one pumps out. I ran it on 90 to max it, it was 20 degrees or so out, maybe 30 (was fighting freezing point early on, then it froze)
When I took it out for a test last night, it got hot pretty fast, so I turned the temperature down to 70º. This morning, it was about 35º on my drive to work, and I still had it set at 70º with the fan on Auto. About halfway to work (30 minute drive), I remembered a small thermometer I had in the car and stuck it on the carpet under the ducts. Got up to 110º pretty fast. Cooler air was coming out of the defroster vents, but it was very comfortable.

I would expect that if I stuck a thermometer into the duct itself, the temperature would be a good deal higher.
Re: Replacing Heater Core 91 DeVille—Any advice?

I just attemped to do my heater core this afternoon. Got everything inside done then I moved onto the hoses. 2hours later I still dont have either one off. From what I read on here I guess I should just use a chisel and break the hoses off my old core? Do all the cores have plastic ends? I dont want to try pounding it off then discover its metal because I'll have an even bigger mess on my hands. Any input is appreciated.
Re: Replacing Heater Core 91 DeVille—Any advice?

The old core (which is OEM as far as I know) had plastic inlet and outlet tubes with those cursed spring-type hose clamps. I managed to wriggle the top hose one off, but was having trouble with the bottom one, so I wriggled the heater core enough to break the bottom inlet tube.

Make sure you've got some old rags or towels around the core because the bottom hose will likely drip coolant (I spilled some onto the carpet and floor mat, but sprayed them down with Resolve; they appear to be OK). I had not driven the car yesterday and did not drain the radiator (the petcock, like most things on this car, is hard to reach), but I did remove the radiator cap to clear any remaining pressure in the system.

You may still have some trouble getting the remnats of the inlet tube out of the hose. I ended up having the disconnect the hose from the heater control valve, pull it out of the engine bay completely, then use a screwdriver to pry the remnants of the tube off the hose. Rethreading it under the A/C dryer (I think that's what it was), was a bitch.

The new core I bought at NAPA has metal inlet and outlet tubes. Once I got the bottom tube rethreaded into position, it wasn't too horrible getting it back on, but not easy, either.

The top hose was a real battle. There's just no room to work in there. Since the tube is metal, I used a screwdriver to bend it out slightly, giving me a little more room to get the top hose back on.

I may still take the car to my regular mechanic and see if he can get the hoses fully onto the tubes. I could barely get mine past the first indent, and I tightened the screw-on clamps as best I could, but I'm still concerned they might come loose.

Good luck. Sorry to say you're going to need it.
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Re: Replacing Heater Core 91 DeVille—Any advice?

Ok, I got my heatercore done in about 2hours today. I was easily able to break the hoses off the old core using a chisel and then i pulled them out from under the A/C parts (without disconnecting the other ends) and easily removed the clamps and the peices of the old core.

I did have some trouble getting the new top hose back on.. but I was able to get it on just a little bit and put a clamp on it. Then i ran the car for 4 or 5mins and once the hose got hot it slid on the rest of the way easily.

Thanks for all the help guys!

Hi Guys,

I have a question here. Yesterday when its 20 degrees here my heater core decides to crap out on me:want: . im pretty sure its not plugged since i have 0 heat both sides. i found directions for replacement here thru searching, and found a new core for 48 bux in stock at pep boys. ima pick it up after work and replace the old one. in the instructions it says.

If you know it's the heater core, here's the instructions from my recently acquired 1996 service manual
Heater Core
Remove or Disconnect:
1)Negative Battery Cable
2)Partially drain coolant (how extacly do i do this?) (partially???):confused:
3)Glove box unit and right-side lower sound insulator
4) Programmer and electrical connectors. Refer to "Air Conditioning Programmer" in this section.(Can be seen below.)
5)Heater core cover.
6)Inlet and outlet heater hoses from heater core.
7)Two heater retaining screws.
8)Heater core.

Install or connect:
1) Heater core to heater case, securing with two screws.
2)Inlet and outlet heater hoses to heater core.
3) Heater core cover.
4)Programmer and electrical connections. Refer to "Air Conditioning Programmer" in this section.
5) Glove box unit and right-side lower sound insulator.
6)Negative battery cable.
7)Refill cooling system.(how extacly do i do this?) (partially???):confused:
Perform the "Air Mix Valve Adjustment" procedure found later in this section.

Air Conditioning Programmer
Remove or disconnect:
1) Negative battery cable
2) Right-side sound insulator and glove-box unit.
3) Vacuum and electrical connectors from programmer.
4) Programmer from vehicle.
Install or connect:
1) Programmer to vehicle.
2) Vacuum and electrical connectors to programmer.
3) Right-side sound insulator and glove box unit.
4) Negative battery cable.

Air Mix Valve Adjustment(Actually, the book calls this "Air Mix Valve Actuators" but I think it's what the service manual meant - Cadillac
mechanics, does that sounds right?)
Remove or disconnect:
1)Glove box
2)Unsnap rod from the plastic retainer on the actuator arm.
3) Two (2) screws from actuator.
4)Electrical connector.
6) Check air mix door for free travel.
Install or connect:
1) Actuator.
2) Electrical connector.
3) Two (2) screw to actuator.
4) Snap rod to plastic retainer on actuator arm.
5) Glove box.
IMPORTANT: After the actuator(s) has been replaced, the actuator(s) need to be recalibrated for proper travel. The ignition must be cycled ON
for 3 minutes to allow the programmer and the actuator(s) to recalibrate for proper travel.
up there in red how do i partially drain/refill the coolant? what the procedure? please respond i know you guys are excellent on this forum thats why i only come here for advice. TIA ALOT!:thumbsup:
i hate to bump this so quick but im lookin for a answer b4 i leave work......its REALLY cold outisde and i really wanna knock this out today any advice would be greatly appreciated.
Heater cores usually do not just "crap out". They slowly clog or start to leak. If you are suddenly getting no heat, I would suspect a different problem. Is the blower working? That is a far more common problem. Been there, done that.
The blower was just replaced and it was blowing only cold air. so i drained the coolant reconnect that hose then popped out the sound insulator and the glovebox just to discover that the damn bland door got stuck...AARRGgghh. so i disabled the blend door from staying on the cold side and i now have heat and am takin back the heater core today. DOH!
Was the air mix door linkage disconnected or is the actuator bad?
the actuator is bad. it was totally stuck. for a quick fix i took the arm off and luckily it was spring loaded to the heat side (yeessssss). NOW when it gets warm again i will have to replace the actuator right? is that fairly easy/cheap? just a ballpark.
Whats a good way to keep the heater core from getting clogged?
And does flushing help?
Yup you'll have to R & R the actuator. I have never had to do one but it is kinda tight in there as you have already seen. Search for a post about actuators. I think Ewill3rd once talked about it. No idea on price.

I have never had a clogged heater core yet, though I have read about some. I would think flushing is the best medicine.
HELP heater core replacemant

I'm prepairing to replace the heater core in my 96DeVille. Any one out there done it? Any pointers?? Near as I can see it shouldn't be too bad. Worst part is fittng myself under the dash!

Glove box out
Sound panel off

Looking to see how to get to the A/C programer. Does it come out then the bracket holding it?
What holds the heater core cover - actually which is the heater core cover. I'm guessing it comes off to the rt side not off into the cabin.
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