Leaking Heater Box Disassembly

So do you find water puddling up on the passenger side floor board? And cant find the leak? 99.99999999% of the time, if not 100% of time its the heater box. All b bodies from 77-90 are notorious for leaking. Its a common rust area, and over time the sealer in the heater box dries out and cant hold water so it comes in. The seal around the firewall can normally be reused, but youll have to fix the rust damage, but i recommend replacing the firewall seal with the general automotive weather strip, that you can find at your local auto parts store. Its quite a fun project, you need to remove the fender to take it off, you may be able to get away with removing the wheel well, but the whole fender is easier, and its actually not very heavy like I thought it would be. If you do find yourself doing this, use a silicon sealer and glue all the seams in the heater box, because if you only fix the seal around the firewall, your still leaving a chance that the heaterbox itself will leak, if its not already. Once you take it apart youll see how its designed, youll need to take it all apart to remove the old glue, just silicon it all up, and it should be all she wrote!

Looks like an adventure. The heater box on my Cutlass was leaking a few weeks ago. I didn't have to go as far as you did to fix mine though.

I definitely wouldn't ditch it completely. It's worth it to keep the heat for the fall or winter evenings.

Yeah, im gonna keep it, i might even put the ac back in one day. It wasnt leaking.... yet haha, but i had a problem with my other caprice that did, and it would fill the passenger side up with water when it rained, so i just wanted to be safe, but its garage kept anyhow. And yeah, i gotta get me a set of those window sweeps too, dont know how long they'll be around!!

Yeah I think it is the box in my car that leaks at the seal. Question for you how big is that hole do you know

exactly? I think what I'd like to do is get a piece of aluminum and cover it and cut the holes for the older style

NON AC almost like  this one actually like the NOVA which is also older Caprice\Impala.



Or you think it is easier to hack the front off of the original and put a sheet there I have seen that.

Or install an AC delete box.  

Um hmm, I can get one of those still too.
(and the AC delete controls, etc.)

I was thinking of the older ones as they look less bulky then the later but you are right. It would involve issues with the controls and vent etc etc. Yeah I need AC delete then as I don't need this box and it takes too much space up. Where's a good pic of the B body AC less version.

Do you know if you can take the top off without removing body parts?

Yeah you can take the top off without removing the body parts.

I have seen a lot of people do something like this mod the existing box basically chop the offending nose

off it.



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Maybe I can do that without removal for now and then pull it and check seal in maybe July when it's warmer.


PS Thanks I got it off pretty easily except for the 78 little screws it was a breeze

Well I decided no to get too crazy as cutting in car proposed too many possible problems.

I instead removed the rest of the AC and partitioned the box to increase heater flow and sealed it up with

a piece of sheetmetal (I will paint it later). It was time to clean\seal that box anyway (dirty and leaky) and I

fixed my windshield washers, hopefully my heat will be a little more forceful.

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Myloth wrote:I fixed my windshield washers,

What did that turn out to be?

Ah the copper sprayers were clogged I took them off cleaned them and blew them out.

Hey guys,

so I followed this thread and I'm pretty sure this problem nailed what I'm seeing in my car. I have a 79 parisienne and is pools on the passenger footwell after raining. Pretty damn sure it's not coolant, the level remains the same in the return jug and doesn't smell of coolant and yeah only pools after rain. This car is my daily driver I don't have time to pull the inner and outer fenders off. Question is, does this leak on to anything like wires/electrical components? Should I just live with it.
An idea though, would I be able to get away with drilling a hole for a drain maybe? is the low spot where it starts to pool on the side away from the inside of the dash? or is it angled toward the dash where that foam gasket is?
Or perhaps a small condensate drain I can hook up to a leak detector?

Welcome to the forum! The heater box already has a built in drain at the lowest point of the box, however the way they designed the box, a portion of it is on the inside of the car and once the tar or whatever sealer they used dried out, itll start leaking no matter what you do, i would not and could  live with it, but thats me, considering these cars are getting rarer and rarer. The carpet will start molding and the floor boards will rust, i caught mine early when it started to leak and my floor boards rusted quick!  Ive also confirmed that you dont have to remove the fender to get it out. You just have to loosen the inner fender, you dont have to remove that either, just enough room to get to the bottom 3 screws. Ive done it so many times i can have it out in less than a half hour, but its something i wouldnt ignore....

Thanks buddy.
hmm interesting might be viable then on a weekend, right now its leaking and pooling on my rubber floor mat not actually going on to the floor, but that's besides the point. the car is pretty mint besides this.
do you have any pictures of when you removed it? are your heater and evap coils deleted? i can see this being a huge pain in the ass.
Id much rather try to fix the drain if it's possible than take the whole box out

I'm glad this thread was recently bumped up so I didn't have do search for my problem.  I mentioned in the headliner thread that I have new carpeting to install and when I pulled out the old stuff it was soaked.  The other morning it was raining when I got home from work so I decided to look and see if I could see the leak with all the carpeting out.  Unfortunately the car doors were locked and I didn't much feel like running inside to get the keys so I just looked through the window.  Sure enough I could see a trickle of water running down just to the right of the center hump coming from under the dash.  I never did look up under there later but now that I have seen this thread I imagine the heater box is going to be my problem.

Is it possible to take this apart enough to fix the leak with the heater core and a/c evaporator in place?  I recently recharged the a/c and would prefer to not have to drain it.  I guess the heater core wouldn't be too bad if I had to remove it, and if I do I might as well just put in a new one at that point.  I don't imagine they cost all that much.

I plan to do the same, the heater core is like $35. Mine is leaking from the same spot though I thought it was leaking onto just my mat but upon closer inspection the carpet is soaked.

You can remove the evap core without evacuating the system, cause of the rubber lines, itll be more difficult but should be possible. You dont have to remove the whole box, but its better to do the job once and for all. Most of them will have rust damage along the seam of the box and gasket on the firewall. If you dont want to tackle that, just silicon all around it and just seal off the inside of the box. I bought a tube of bathroom clear silicon from lowes, youll need alot.

Well, I started on this project this evening.  It wasn't ideal but I decided to do it out in the driveway since I would have to move other projects to get it in the garage.  It wasn't bad while the sun was still out but once it started going down the temp dropped to around 40 and was going down from there.

It took me quite a while but I do have the heater box assembly out of the car and ready to pull apart and reseal it.  I opted to remove the inner fender completely but not to remove the entire outer fender with it, mostly because I didn't have anybody handy to help take the hood off, and I've never been a fan of working with a hood propped in place with one hinge removed.  It would definitely be possible to remove the heater box by just loosening up the back of the inner fender as was mentioned earlier in this thread but I decided to just get it out of the way.  That also gave me a chance to clean up the battery tray and around that area.

The heater box itself wasn't that hard to remove.  I fought a bit with getting the top off just because a couple of the bolts were hidden under some built up debris down in the well area below the windshield.  Once I located those the top came right off.  I had no problem with pulling the evaporator out with the hoses still attached, also as someone mentioned earlier.  There was plenty of play to swing that entire assembly up towards the front of the car and out of the way.   I left the heater core in the box until it was removed and just pulled the hoses off.  I lost very little coolant taking it out.  

The biggest problem I had was figuring out where to disconnect the wires and vacuum lines that run through the heater box.  I ended up disconnecting everything from under the dash  and then all the wires just came out with the heater box.  Looking back it was quite a project and there may have been an easier way.  Too late now.  I'm still hoping to get some time on it tomorrow but I have some other things going as well and I also still need to pick up some weatherstrip and silicon first.  There is a little bit of rust to fix but nothing serious.  Looks like part of my problem was the drain was just about completely plugged.  The sealant was also pretty bad in at least one spot so it probably would have leaked anyway, but the plugged drain likely made it worse.

I was pretty tired of working on it by the time I called it quits for the night.  There is no turning back now though--just have to find the time to get it back together.

Its good your catching the problem now, dont need to see any more rust damage and mold to these increasingly rare cars.

GM B-Body Forum wrote:Its good your catching the problem now, dont need to see any more rust damage and mold to these increasingly rare cars.

I'm glad I found this forum and especially this thread about the leaking heater box.  If I hadn't read the details about this I probably would have just tried to seal it up around the firewall and ended up with bigger problems down the road.  The timing sucked because I really didn't have time for this, but I'm glad I am fixing it before putting all the new padding and carpeting in.

I have a question somewhat related to this project that maybe someone can help with.

There are two hard plastic vacuum lines that run from the engine compartment through the bottom of the heater box along with the wiring.
On the inside they both go to the heater/AC control lever assembly in the dash.  In the engine compartment one of the lines goes to the round vacuum tank that is mounted on the heater box.  That appears to be the vacuum source for the controls and the controls all work fine.  As I started looking over what all I needed to remove to get the heater box out I noticed the other vacuum line just ends about a foot or so from where it comes out of the heater box.  What I need to know is where that line is supposed to be connected to?  I couldn't find anywhere that looked like it was missing a line.  The end that is just sitting there looks like it was broken off at some point so the other end could have come from anywhere.  

The only thing I could think of under the hood that would need to be controlled by the heater/ac controls would be a shut-off for the coolant into the heater core which I have seen on various vehicles in the past.  Did these cars have one of these valves or is there somewhere else that this vacuum line would have been connected to?  I must have a vacuum leak at this open line when the control lever is in a certain position but with the heater core currently out I haven't tested it.  If I can't figure out where it connects to I will just plug the line for now I guess.

Any ideas?

I found my answer first thing this afternoon when I opened the hood.  It was right in front of me and I'm not sure how I missed it.  As I suspected there is a shut-off valve for the coolant going into the heater core for when the AC is on.  I just expected it to be right next to the heater core where I have seen them on other cars and instead it is in front of the air cleaner closer to where the heater hose comes off of the water pump.  I don't have any of that plastic line so I guess I will just splice in some regular vacuum hose.

I just wanted to mention when I pulled the top of heater\AC box I resealed the top seam with sealant and my

leaking problem evaporated.(pun intended) It would seem the leaking issue was primarily with that

top seam for me anyhow. I don't believe the windshield leaks much just a weep at the top passenger side.