Evaporator housing "gunk" + leak

[adamj]

Working on getting my ac up and running, and I see this black stuff oozing out of the black enclosure for the evaporator:

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Is this an oil leak from the ac lines? Or is this a sealant of some sort?
When I have the blower going (heat or AC) I can feel leakage of air coming out.
Any tips on sealing this up?

 

[chengny]

No, not an oil leak.
As you suggest, it's just sealant. Actually it's the GM factory installed sealant - a 3M product called Strip-Calk (sic).

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If - for whatever reason - you had to disassemble the entire evaporator you would find it used to seal a couple of other joints as well:

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I works well and normally stays put forever. Doesn't usually ooze like yours.

Anyway, I don't use it because the stuff is kind of expensive ($20 as shown above) and difficult to find sometimes. But the biggest drawback is that it is only sold in boxes containing 60 feet which results in a lot of waste - unless you are in the business and can use it up.

A couple of better alternatives are black silicone sealant and common foam rubber weather stripping (like for household windows and doors).

The silicone is used to seal the aluminum tubing penetrations in the evap casing and also where the heater core nipples pass through the fan housing:

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Seal the joint between the evap casing halves with silicone (yellow) and seal the assembled evap/fan housing to the firewall with the foam weatherstripping (red):

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[adamj]

By black silicone sealant, do you mean the black RTV gasket stuff?

 

[chengny]

No, just GE Silicone II in the caulking gun size tube. Here - it's like $6 at Lowes:

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[hatzie]

The problem with silicone is it actually cures. Silicone is great for the housing halves. The Silicone is too runny to fill big gaps like the holes around the evaporator tubes. It'll puddle inside and glue the evaporator into the housing.
I would use the 3M strip calk around the big gaps where the evaporator lines penetrate the fiberglass.

 

[adamj]

What about seam sealer that is used for body panels, could that be used for the larger hole? I ask because I already have some that I used recently for the wheel well.

 

[Georgeb]

You could pick up some of this stuff:
http://www.lowes.com/pd_13591-1781-..._Bender&CAWELAID=&CAWELAID=320011480000363554

Dad always has some around for electrical work and it does work really well.

 

[hatzie]

I'd use what we used to call Dum Dum tape. The actual trade name for it is Prestite tape.
http://www.acsource.com/prestitetape.aspx
http://www.amazon.com/CoolPro-Climate-Control-Products-Prestite/dp/B000FS3UHW
http://www.autozone.com/sealants-glues-adhesives-and-tape/tape/santech-prestite-tape/158980_0_0/

It's a gooey sticky cork impregnated non-hardening butyl extruded into a long flat tape and rolled up on a wax paper tape. It's specifically made for sealing air holes around AC hard-lines in buildings and vehicles.