#1  
Old 08-09-2022, 07:39 PM
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i4abuygto i4abuygto is offline
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Default Crack in AC evaporator box - how to repair.

I just pulled the heater core and I am installing a new core and (even though the old fan still works), a new fan motor. I plan on fixing system to working AC eventually. When pulling heater core, I noticed a pretty good crack in the evaporator box behind the passenger side head.
With the dash currently out and the heater core box out I can get at the crack from the inside of the car- has anyone patched these boxes before?
Can I just use a good plastic epoxy?
I thought of maybe using some reinforcement mesh along with the epoxy.
I want to get it right the first time because these are a b**** to get at when the dash is in.
Let me know your thoughts.
Thanks

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Old 08-10-2022, 09:54 AM
MO Olds MO Olds is offline
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I have seen and used fiberglass resin and mesh but it was out of the car ( much easier to work with). I think expoxy like you said would also be a great alternative; one for plastic and a fresh tube. Then you don't have to worry about sanding it either if you are not too worried about looks. If you happen to have fiberglass resin around you don't necessarily need the mesh depending on size of the crack, especially if it's hard to get to. Good luck!

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Old 08-10-2022, 11:20 AM
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mzbk2l mzbk2l is offline
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Do you know what material the box is constructed of? If it's any kind of plastic that will melt, I just bought and used one of these plastic stapler welder guns for $28 on Amazon; it did a great job on a broken fender tab on my Hayabusa and I came away pretty impressed.
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Old 08-10-2022, 09:27 PM
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i4abuygto i4abuygto is offline
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Thanks for the input- I will try the plastic epoxy and then maybe fiberglass over that if I think it needs more.
I appreciate the input
Thank you.

  #5  
Old 08-10-2022, 10:57 PM
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i4abuygto i4abuygto is offline
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When looking at the evaporator box crack and broken area it looks like the material has fibers in it - is the box fiberglass or a composite of some kind? I want to use the right epoxy for the repair. If it is not plastic, that changes the equation quite a bit.

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Old 08-10-2022, 11:54 PM
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I am truly guessing but I thought the material was a "heavily" fiber-reinforced thermoset when I replaced the heater core and cleaned mine up. It is a big part for that material, but back then they may have justified the manufacturing cost to obtain a material property not available in the thermoplastics of the day....like strength at high temperature.

If so, epoxy would likely bond OK but without the fiber reinforcement, it is unlikely to be as strong as original. Your idea to reinforce with fiberglass cloth makes good sense.

Given the uncertainty about material, I'd sand a small test area, bond a nail-head, metal bolt, or similar "stub" with the adhesive resin (slow-cure epoxy is a good starting point) you think will work. Pull it to failure. If it rips off a little of the case or leaves adhesive on both surfaces (cohesive failure), you know it made a decent bond. If it fails at an interface (adhesive failure) it might not hold up well long-term and you can try a different adhesive. There are some really strong 2-component acrylic-based structural adhesives that might work if epoxy doesn't. 3M would be one source.

  #7  
Old 08-15-2022, 11:38 AM
Warren Seale Warren Seale is offline
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If the box is not disturbed then there shouldn't be much stress on it other than temperature changes. So just filling the crack with epoxy should work to seal it up. Larger cracks can use epoxy putty. I don't think a fiber cloth is required in this case. The material originally used looks like fiberglass/resin.

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  #8  
Old 08-20-2022, 11:30 AM
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Thanks all for your help. I used the J B Weld Plastic Bonder - black with fiberglass cloth to reinforce the corners that were cracked. Seems to work great and finish looks good. It is sand able after it cures and hardens, if needed. The area I repaired won't be seen so I didn't have to do much finish work.
The JB Weld Plastic bonder specifically says it is for thermoset and fiberglass repairs.
I would recommend using the fiberglass cloth as it helps to hold the material in place and fill gaps.
I also used it to repair some of the plastic ducting that was cracked and to repair some missing mounting holes.
I did roughen all areas up with sand paper to make sure all areas were clean and would get better adherence.
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Last edited by i4abuygto; 08-20-2022 at 11:36 AM.
  #9  
Old 08-22-2022, 11:46 AM
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That's good stuff; I used it to repair a mustang cobra door panel that had split in half from end to end... as far as I know, it's still holding up.

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